The American Smoketree

Photo by Andrew Ward licensed under CC BY-NC 2.0

I am a sucker for smoketrees (Cotinus spp.). These members of the cashew family (Anacardiaceae) are a common sight around my town and really put on a dazzling show from late spring through fall. When I finally got around to putting a name to these trees, I was a little bit bummed to realize that all of the specimens in town are representatives of the Eurasian species, Cotinus coggygria, but it didn’t take me long to find out that North America has it’s own fascinating representative of the genus.

The American smoketree (Cotinus obovatus) is not terribly common in the wild or cultivation. Today, it exhibits a suffuse distribution through parts of southern North America, with disjunct populations occurring along the Ozark Plateau of Arkansas and Missouri, the Arkansas River in eastern Oklahoma, the Cumberland Plateau in northeastern Alabama, Tennessee, and Georgia, and the Edwards Plateau in west-central Texas. The major habitat feature that unites these populations is soil. All of them are said to grow on rocky, calcareous soils prone to drought.

Photo by Megan Hansen licensed under CC BY-SA 2.0

It is an interesting distribution to say the least. I haven’t found too much in the way of an explanation for why the American smoketree is limited to calcareous soils in the wild. Apparently it is fairly adaptable to different soil types in cultivation. Perhaps competition with other species limits this tree to harsh conditions. It isn’t a big species by most standards. The American smoketree generally produces multiple stems and only occasionally reaches heights of 30 feet (9 meters) or more in most circumstances. One phrase that gets repeated with some frequency is that the American smoketree likely represents a relictual species.

Though hard to prove without ample fossil evidence, it seems many experts believe that American smoketrees (and the genus Cotinus in general) were far more common and widespread in the past than they are today. Indeed, the fossil remains of a species named Cotinus cretaceus (sometimes C. cretacea) were found in Alaska and date back to the late Cretaceous. Given that the American smoketree’s closest living relatives are found throughout parts of Europe and Asia, such evidence suggests that this genus spread into North America during a period when land bridges connected the two continents and has since been reduced to scattered populations of this single North American species.

Photo by Andrey Zharkikh licensed under CC BY 2.0

European colonization of North America did not help the American smoketree either. American smoketree sap can be processed into a yellow dye, which was highly coveted during the American Civil War. Its rot-resistant wood was also widely used for fence posts. At least one source I found indicated that the tree was cut to near extirpation in many areas for these reasons. Luckily today, with harvesting pressures largely a thing of the past, the American smoketree has rebounded enough that it is currently considered a species of least concern.

The American smoketree has also benefited from some minor popularity in cultivation. Like its Eurasian cousins, the appeal of this species comes from its colorful foliage, wonderfully flaky bark, and billowy inflorescences. Its egg-shaped leaves emerge in spring and are silky and pink. As spring gives way to summer, the leaves gradually turn a pleasing shade of blueish-green. Come fall, the leaves paint the landscape in bright red until they are shed. Late spring is generally the blooming time for American smoketree.

Photo by geneva_wirth licensed under CC BY-NC 2.0

Photo by peganum licensed under CC BY-SA 2.0

Its tiny, inconspicuous flowers are borne on large, branching panicles. Each panicle is covered in tiny hairs that apparently continue to grow well after the flowers have been pollinated. This is where the name smoketree comes from. From afar, a tree covered in panicles looks as if it is billowing dense clouds of smoke from its canopy. The whole spectacle is stunning to say the least and I just wish this species was more popular than its cousins.

All in all, the American smoketree is a truly interesting species. From its fractured distribution and curious history to its status as an obscure native tree in cultivation, there are a lot of reasons to love this species. Though related to plants like poison ivy (Toxicodendron spp.), smoketrees only rarely cause dermatitis in particularly susceptible individuals. I hope I get the chance to see an American smoketree in the wild some day.

Further Reading: [1] [2] [3] [4] [5]

Krassilovia: An Amazing Cretaceous Conifer

Reconstructing extinct organisms based on fossils is no simple task. Rarely do paleontologists find complete specimens. More often, reconstructions are based on fragments of individuals found either near one another or at least in similar rock formations. This is especially true for plants as their growth habits frequently result in fragmentary fossilization. As such, fossilized plant remains of a single species are often described as distinct species until subsequent detective work pieces together a more complete picture.

Such was the case for the fossil remains of what were described as Krassilovia mongolica and Podozamites harrisii. Hailing from the Early Cretaceous (some 100-120 million years ago), Krassilovia was only known from oddly spiny cone scales and Podozamites was only known from strap-shaped leaves found in a remote region of Mongolia. Little evidence existed to suggest they belonged to the same plant. That is, until these structures were analyzed using scanning electron micrographs.

(A–C) Articulated seed cones, (D) Isolated cone axis, (E) Incomplete leafy shoot showing a cluster of three attached leaves, (F) Three detached strap-shaped leaves, G) Detail of A showing tightly imbricate interlocking bract-scale complexes, (H) Detail of leaf apex showing converging veins, (I) Three isolated bract-scale complexes showing abaxial (top) and adaxial (bottom) surfaces, (J) Two isolated seeds showing narrow wings. [SOURCE]

These fossilized plant remains were preserved in such detail that microscopic anatomical features such as stomata were visible under magnification. By studying the remains of these plants as well as others, scientists discovered some amazing similarities in the stomata of Krassilovia and Podozamites. Unlike other plant remains associated with those formations, the Krassilovia cone scales and Podozamites leaves shared the exact same stomate morphology. Though not without some uncertainty, the odds that these two associated structures would share this unique morphological trait by chance is slim and suggests that these are indeed parts of the same plant.

The amazing discoveries do not end with stomata either. After countless hours of searching, fully articulated Krassilovia cones were eventually discovered, which finally put the strange spiky cone scales into context. It turns out those spiked scales interlocked with one another, with the two bottom spikes of one scale interlocking with the three top spikes of the scale below it. In life, such interlocking may have helped protect the developing seeds within until they had matured enough to be released. Also, the sheer volume of cone scales coupled with other minute anatomical details I won’t go into here indicate that, similar to Abies and Cedrus cones, Krassilovia cones completely fell apart when fully ripe.

Though not related, the cone scales of the extinct Krassilovia (left) show similarities with the cone scales of modern day Cryptomeria species (right).

Interestingly, the ability to resolve microscopic structures in these fossils has also provided insights into some modern day taxonomic confusion. It turns out that Krassilovia shares many minute anatomical similarities with present day Gnetales. Gnetales really challenge our perception of gymnosperms and their superficial resemblance to angiosperms have led many to suggest that they represent a clade that is sister to flowering plants. However, more recent molecular work has placed the extant members of Gnetales as sister to the pines. Evidence of shared morphological features between extinct conifers like Krassilovia and modern day Gnetales add some interesting support to this hypothesis. Until more concrete evidence is described and analyzed, the true evolutionary relationships among these groups will remain the object of heated debate for the foreseeable fture.

What we can say is that Krassilovia mongolica was one remarkable conifer. Its unique morphology clearly demonstrates that conifers were once far more diverse in form and function than they are currently. Even the habitat in which Krassilovia once lived is not the kind of place you can find thriving conifer communities today. Krassilovia once grew in a swampy habitat. However, whereas only a few extant conifers enjoy swamps, Krassilovia once shared its habitat with a wide variety of conifer species, the likes of which we are only just beginning to appreciate. I for one am extremely excited to see what new fossil discoveries will uncover in the future.

LISTEN TO EPISODE 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS FOSSIL AND THE ECOSYSTEM IN WHICH IT ONCE EXISTED.

Photo Credits: [1] [2] [3]

Further Reading: [1]

Southern Beeches and Biogeography

If you spend any time learning about paleontology, you are bound to come across at least one reference to the southern beeches (genus Nothofagus). This remarkable and ecologically important group of trees can be found growing throughout the Southern Hemisphere at high latitudes in South America, Australia, New Zealand, New Guinea, and New Caledonia. Not only are they prominent players in the forests in which they grow, their fossil history has provided scientists with invaluable data on plate tectonics and biogeography.

Southern beeches may not be the tallest trees in any forest but that doesn’t mean they aren’t impressive. Numbering around 37 species, southern beeches have conquered a range of climate zones from temperate to tropical. Those living in lowland tropical forests tend to be evergreen, holding onto their leaves throughout the year whereas those living in temperate or montane habitats have evolved a deciduous habit. Some species of southern beech are also known for their longevity, with individuals estimated to be in excess of 500 years in age.

Nothofagus alpina

Anyone familiar with the true beeches (genus Fagus) will quickly recognize many similarities among these genera. From their toothy leaves to their triangular nuts, these trees are strikingly similar in appearance. Indeed, for much of their botanical history, southern beeches were included in the beech family (Fagaceae). However, recent molecular work has revealed that the southern beeches are genetically distinct enough to warrant their own family - Nothofagaceae.

The beech-like fruits of Nothofagus obliqua var. macrocarpa

As mentioned, the southern beeches, both extant and extinct, have been important players in our understanding of plate tectonics. Their modern day distribution throughout the Southern Hemisphere seems to hint at a more concentrated distribution at some point in the past. All of the continents and islands on which they are found today were once part of the supercontinent of Gondwana, which has led many to suggest that the southern beech family arose before Gondwana broke apart during the Jurassic, with ancestors of extant species riding the southern land masses to their modern day positions. Indeed, the paleo record seems to support this quite well.

Fall colors of Nothofagus cunninghamii.

The southern beeches have an impressive fossil record that dates back some 80 million years to the late Cretaceous. Their fossils have been found throughout many of the Southern Hemisphere continents including the now-frozen Antarctica. It would seem that the modern distribution of these trees is the result of plate tectonics rather than the movement of seeds across oceans. This is bolstered by lines of evidence such as seed dispersal. Southern beech nuts are fairly large and do not show any adaptations for long distance dispersal, leading many to suggest that they simply cannot ocean hop without serious help from other forms of life.

Nothofagus fusca

However, life is rarely so simple. Recent molecular work suggests that continental drift can’t explain the distribution of every southern beech species. By studying trees growing in New Zealand and comparing them to those growing in Australia and Tasmania, scientists have discovered that these lineages are far too young to have originated before the breakup of Gondwana. As such, the southern beeches of Austrialasia more likely got to their current distributions via long distance dispersal events. Exactly what allowed their seeds to cross the Tasman Sea is up for debate, but certainly not impossible given the expanse of time available for rare events to occur. Regardless of where anyone stands on this recent evidence, it nonetheless suggests that the biogeographic history of the southern beech family isn’t as clear cut as once thought.

Nothofagus fusca

Unfortunately, while southern beeches hold a prominent place in the minds of naturalists, the same cannot be said for the rest of the world. Little care has been given to their scientific and ecological importance and massive quantities of these trees are logged each and every year. Today it is estimated that 30% of all southern beech species are threatened with extinction. Luckily, large portions of the remaining populations for these trees are growing on protected lands. Also, because of their scientific importance, numerous southern beeches can be found growing in botanical collections and their seeds are well represented in seed banks. Still, southern beeches and the forests they comprise are worthy of respect and protection.

Photo Credits: [1] [2] [3] [4] [5] [6]

Further Reading: [1] [2] [3]

History of Grass Evolution Written in Dinosaur Poop

Photo by Sugeesh licensed by CC BY-SA 3.0

Grasses dominate our planet today but that has not always been the case. Because of both their ecological and cultural importance , the origin and diversification of grasses has long been a hot topic in biology. We know that grasses really hit their stride following the extinction of the dinosaurs, and that they changed herbivore anatomy in a big way, but their origins remain shrouded in mystery. Recently, a discovery made in fossilized dinosaur poop has shone a surprisingly bright light into the history of grasses on our planet.

Prior to this discovery, the earliest evidence of grasses came in the form of fossilized pollen and tiny pieces of silica called phytoliths. Phytoliths are essentially tiny pieces of glass that serve as a form of defense against herbivores. Because they are made of silica and fossilize well, phytoliths turn up frequently in the fossil record. This makes them extremely useful for finding evidence of grasses even where whole-plant fossilization is unlikely.

Illustration by Nobu Tamura (http://spinops.blogspot.com) licensed by CC BY-NC-ND 3.0

Whereas phytoliths are not unique to grasses, their form is often taxon-specific. With a good eye and a bit of training, one can look at a phytolith under a microscope and tell you what type of plant it came from. This is where the dinosaur poop comes into the picture. By examining fossilized dinosaur poop from India, paleontologists can get an idea of what dinosaurs were eating.

By examining the fossilized poop of a group of large herbivorous dinosaurs called Titanosaurs, paleontologists now have a better idea of grass diversity in the late Cretaceous. They have uncovered a surprising diversity of phytoliths, which demonstrate that at least 5 distinct grass taxa that we would recognize today were alive and well some 100.5 to 66 million years ago. These include extant groups like Oryzoideae (think rice and bamboo), Puelioideae, and Pooideae (think wheat, barley, oat, rye, and many lawn and pasture grasses). There were other lesser known lineages mixed in there as well.

Fossilized dinosaur poop or “coprolite.” USGS Public Domain

These findings are exciting for a variety of reasons. For one, it tells us that despite lacking teeth specialized for eating grasses, large herbivorous dinosaurs like the Titanosaurs were nonetheless incorporating these plants into their diet. It also tells us that grasses were already quite diverse by the late Cretaceous. The fact that modern clades of grass were around back then sets back grass evolution many millions of years. It also tells us something about grass biogeography. It suggests that grasses were already wide spread across the supercontinent of Gondwana long before India broke away. Finally, it tells us that grasses evolved silicate phytoliths long before more recognizable grass-eating herbivores came onto the scene.

I am always blown away by the details paleontologists are able to extract from such tiny fossils. Who knew dinosaur poop could tell us so much?

Photo Credits: [1] [2] [3] [4]

Further Reading: [1]

A Herbaceous Conifer From the Triassic

It is hard to make broad generalizations about groups of related organisms. There are always exceptions to any rule. Still, there are some “facts” we can throw around that seem to apply pretty well to specific branches on the tree of life. For instance, all of the gymnosperm lineages we share our planet with today are woody, relatively slow to reach sexual maturity, and are generally long-lived. This has not always been the case. Fossil discoveries from France suggest that in the past, gymnosperms were experimenting with a more herbaceous lifestyle.

The fossils in question were discovered in eastern France back in the 1800’s. The strata from which they were excavated dates back to the Middle Triassic, some 247 million years ago. Immortalized in these rocks were numerous spindly plants with strap-like leaves and a few branches, each ending in what look like tiny cones. Early interpretations suggested that these may represent an extinct lycopod, however, further investigation suggested something very surprising - a conifer with an herbaceous growth habit.

Indeed, thanks to even more scrutiny, it is now largely agreed upon that what was preserved in these rocks were essentially herbaceous conifers. The fossils were given the name Aethophyllum stipulare. They are wonderfully complete, depicting roots, shoots, leaves, and reproductive organs. Moreover, the way in which they were fossilized preserved lots of fine-scale anatomical details. Taken together, there are plenty of clues available that allow paleobotanists to say a lot about how this odd conifer made a living.

For starters, they were not very big plants. Not a single specimen has been found that exceeds 2 meters (6.5 ft) in height. The main stem of these conifers only seem to branch a couple of times. Cones were formed at the tips of the upper branches and not a single specimen has been found that depicts subsequent growth following cone formation. This suggests that Aethophyllum exhibited determinate growth, meaning that individuals grew to a certain size, reproduced, and did not continue to grow after that. Female cones were situated at the tips of the upper most branches and male cones were situated at the tips of lower shoots. The smallest reproductive individuals that have been unearthed are only 30 cm (11 in) in height, which suggests that Aethophyllum  was capable of reproducing within a few months of germination.

Artists reconstruction of Aethophyllum stipulare

Amazingly, researchers were also able to extract fossilized pollen and seeds from some of the Aethophyllum cones. The pollen itself is saccate, much like what we see in many extant conifers. By comparing the morphology of the pollen extracted from the cones to other fossil pollen records, researchers now feel confident that Aethophyllum is the source of pollen grains discovered in sediments from western, central, and southern Europe, Russia, Northern Africa, and China, suggesting that Aethophyllum was pretty wide spread during the Middle Triassic. Aethophyllum seeds were small, ellipsoid, and were not winged, likely germinating a short distance from the parent.

The stems of Aethophyllum are interesting in the own right. Thanks to their preservation, cross sections have been made and they reveal that these plants only ever produced secondary tracheids and primary xylem. The only place on the plant where any signs of woody secondary xylem occur are at the base of the cones. This adds further confirmation that Aethophyllum was herbaceous at the onset of sexual maturity.

Another intriguing aspect of the stem is the presence of numerous large air spaces within the stem pith. Today, this anatomical feature is present in plants like bamboo, Equisetum, and the flowering stalks of Agave, all of which exhibit alarmingly fast growth rates for plants. This suggests that not only did Aethophyllum reproduce early in its life, it also likely grew extremely fast.

1. Smallest fertile plant in the Grauvogel and Gall collections, with two stems extending from the root, and terminal ovulate cone (OC) on one branch (scale bar=10 cm). 2. Cross-section of stem in the Grauvogel and Gall collections showing cauline bundles with scanty wood (at left, top and right) surrounding large pith with large, aerenchymatous lacunae and interspersed pith parenchyma cells. Vascular cambium, phloem, and more peripheral tissues are not preserved (scale bar=200 μm). 3.Seedling in the Grauvogel and Gall collections showing primary root (R), cotyledons (C) and stem (S) with apically borne leaves (scale bar=10 cm). Quoted from SOURCE

Mature Aethophyllum aren’t the only fossils available either. Many seedlings have been discovered in close proximity to the adults. Seedlings were also exquisitely preserved, depicting hypocotyl, a primary root system, two two-veined cotyledons, and a short stem with four-veined leaves arranged in a helix. The fact that seedlings and adults were found in such close proximity lends to the idea that Aethophyllum populations were made up of multi-aged stands, not unlike some of the early successional plants we find in disturbed habitats today.

The sediments in which these plants were fossilized can also tell us something about the habitats in which Aethophyllum grew. The rock layers are made up of a mix of sediments typical of what one would find in a flood plain or delta. Also, Aethophyllum aren’t the only plant remains discovered. Many species known to grow in regularly disturbed, flood-prone habitats have also been found. Taken together these lines of evidence suggest that Aethophyllum was similar to what we would expect from herbaceous plants growing in similar habitats today. They grew fast, reproduced early, and had to jam as many generations in before the next flood ripped through and hit the reset button.

Aethophyllums small size, lack of wood, and rapid growth rate all point to a ruderal lifestyle. Today, this niche is largely filled by angiosperms. No conifers alive today can claim such territories. The discovery of Aethophyllum demonstrates that this was not always the case. The fact that pollen has been found far outside of France suggests that this ruderal lifestyle worked quite well for Aethophyllum.

The terrestrial habitats of the Middle Triassic were dominated by the distant relatives of modern day ferns, lycophytes, and gymnosperms. Needless to say, it was a very different world than anything that we are familiar with today. However, that does not mean that the pressures of natural selection were necessarily different. Aethophyllum is evidence that specific selection pressures, in this case regular flood disturbance, select for similar traits in plants through time. Why Aethophyllum went extinct is anyone’s guess. Despite how well they have been preserved, there is still a lot of mystery surrounding this plant.

Photo Credit: [1]

Further Reading: [1] [2] [3] [4]

The Creeping Strawberry Pine

Photo by Tindo2 - Tim Rudman licensed under CC BY-NC 2.0

With its small, creeping habit and bright red, fleshy female cones, it is easy to see how Microcachrys tetragona earned its common name “creeping strawberry pine.” This miniature conifer is as adorable as it is interesting. With a fossil history that spans 66 million years of Earth’s history, it also has a lot to teach us about biogeography.

Today, the creeping strawberry pine can only be found growing naturally in western Tasmania. It is an alpine species, growing best in what is commonly referred to as alpine dwarf scrubland, above 1000 m (3280 ft) in elevation. Like the rest of the plants in such habitats, the creeping strawberry pine does not grow very tall at all. Instead, it creeps along the ground with its prostrate branches that barely extend more than 30 cm (0.9 ft) above the soil. This, of course, is likely an adaptation to its alpine environment. Plants that grow too tall frequently get knocked back by brutal winds and freezing temperatures among other things.

The creeping strawberry pine is not a member of the pine family (Pinaceae) but rather the podocarp family (Podocarpaceae). This family is interesting for a lot of reasons but one of the coolest is the fact that they are charismatic representatives of the so-called Antarctic flora. Along with a handful of other plant lineages, it is thought that Podocarpaceae arose during a time when most of the southern continents were combined into a supercontinent called Gondwana. Subsequent tectonic drift has seen the surviving members of this flora largely divided among the continents of the Southern Hemisphere. By combining current day distributions with fossil evidence, researchers are able to use families such as Podocarpaceae to tell a clearer picture of the history of life on Earth.

What is remarkable is that among the various podocarps, the genus Microcachrys produces pollen with a unique morphology. When researchers look at pollen under the microscope, whether extant or fossilized, they can say with certainty if it belongs to a Microcachrys or not. The picture we get from fossil evidence paints an interesting story for Microcachrys diversity compared to what we see today. It turns out, Microcachrys endemic status is a more recent occurrence.

This distinctive, small, trisaccate pollen grain is typical of what you find with Microcachrys whereas all other podocarps produce bisaccate pollen. J.I. Raine, D.C. Mildenhall, E.M. Kennedy (2011). New Zealand fossil spores and pollen: an illustrated catalogue. 4th edition. GNS Science miscellaneous series no. 4. http://data.gns.cri.nz/sporepollen/index.htm

The creeping strawberry pine is what we call a paleoendemic, meaning it belongs to a lineage that was once far more widespread but today exists in a relatively small geographic location. Fossilized pollen from Microcachrys has been found across the Southern Hemisphere, from South America, India, southern Africa, and even Antarctica. It would appear that as the continents continued to separate and environmental conditions changed, the mountains of Tasmania offered a final refuge for the sole remaining species in this lineage.

Another reason this tiny conifer is so charming are its fruit-like female cones. As they mature, the scales around the cone swell and become fleshy. Over time, they start to resemble a strawberry more than anything a gymnosperm would produce. This is yet another case of convergent evolution on a seed dispersal mechanism among a gymnosperm lineage. Birds are thought to be the main seed dispersers of the creeping strawberry pine and those bright red cones certainly have what it takes to catch the eye of a hungry bird. It must be working well for it too. Despite how narrow its range is from a global perspective, the creeping strawberry pine is said to be locally abundant and does not face the same conservation issues that many other members of its family currently face. Also, its unique appearance has made it something of a horticultural curiosity, especially among those who like to dabble in rock gardening.

Mature female cones look more like angiosperm fruit than a conifer cone. Photo by Mnyberg licensed under CC BY-SA 4.0

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

The Rise and Fall of the Scale Trees

Photo by Ghedoghedo licensed under CC BY-SA 3.0

If I had a time machine, the first place I would visit would be the Carboniferous. Spanning from 358.9 to 298.9 million years ago, this was a strange time in Earth’s history. The continents were jumbled together into two great landmasses - Laurasia to the north and Gondwana to the south and the equatorial regions were dominated by humid, tropical swamps. To explore these swamps would be to explore one of the most alien landscapes this world has ever known.

The Carboniferous was the heyday for early land plants. Giant lycopods, ferns, and horsetails formed the backbone of terrestrial ecosystems. By far the most abundant plants during these times were a group of giant, tree-like lycopsids known as the scale trees. Scale trees collectively make up the extinct genus Lepidodendron and despite constantly being compared to modern day club mosses (Lycopodiopsida), experts believe they were more closely related to the quillworts (Isoetopsida).

Carboniferous coal swamp reconstruction dating back to the 1800’s

It is hard to say for sure just how many species of scale tree there were. Early on, each fragmentary fossil was given its own unique taxonomic classification; a branch was considered to be one species while a root fragment was considered to be another, and juvenile tree fossils were classified differently than adults. As more complete specimens were unearthed, a better picture of scale tree diversity started to emerge. Today I can find references to anywhere between 4 and 13 named species of scale tree and surely more await discovery. What we can say for sure is that scale tree biology was bizarre.

The name “scale tree” stems from the fossilized remains of their bark, which resembles reptile skin more than it does anything botanical. Fossilized trunk and stem casts are adorned with diamond shaped impressions arranged in rows of ascending spirals. These are not scales, of course, but rather they are leaf scars. In life, scale trees were adorned with long, needle-like leaves, each with a single vein for plumbing. Before they started branching, young trees would have resembled a bushy, green bottle brush.

As scale trees grew, it is likely that they shed their lower leaves, which left behind the characteristic diamond patterns that make their fossils so recognizable. How these plants achieved growth is rather fascinating. Scale tree cambium was unifacial, meaning it only produced cells towards its interior, not in both directions as we see in modern trees. As such, only secondary xylem was produced. Overall, scale trees would not have been very woody plants. Most of the interior of the trunk and stems was comprised of a spongy cortical meristem. Because of this, the structural integrity of the plant relied on the thick outer “bark.” Many paleobotanists believe that this anatomical quirk made scale trees vulnerable to high winds.

Scale trees were anchored into their peaty substrate by rather peculiar roots. Originally described as a separate species, the roots of these trees still retain their species name. Paleobotanists refer to them as “stigmaria” and they were unlike most roots we encounter today. Stigmaria were large, limb-like structures that branched dichotomously in the soil. Each main branch was covered in tiny spots that were also arranged in rows of ascending spirals. At each spot, a rootlet would have grown outward, likely partnering with mycorrhizal fungi in search of water and nutrients.

A preserved Lepidodendron stump

Eventually scale trees would reach a height in which branching began. Their tree-like canopy was also the result of dichotomous branching of each new stem. Amazingly, the scale tree canopy reached staggering heights. Some specimens have been found that were an estimated 100 ft (30 m) tall! It was once thought that scale trees reached these lofty heights in as little as 10 to 15 years, which is absolutely bonkers to think about. However, more recent estimates have cast doubt on these numbers. The authors of one paper suggest that there is no biological mechanism available that could explain such rapid growth rates, concluding that the life span of a typical scale tree was more likely measured in centuries rather than years.

Regardless of how long it took them to reach such heights, they nonetheless would have been impressive sites. Remarkably, enough of these trees have been preserved in situ that we can actually get a sense for how these swampy habitats would have been structured. Whenever preserved stumps have been found, paleobotanists remark on the density of their stems. Scale trees did not seem to suffer much from overcrowding.

The fact that they spent most of their life as a single, unbranched stem may have allowed for more success in such dense situations. In fact, those that have been lucky enough to explore these fossilized forests often comment on how similar their structure seems compared to modern day cypress swamps. It appears that warm, water-logged conditions present similar selection pressures today as they did 350+ million years ago.

Like all living things, scale trees eventually had to reproduce. From the tips of their dichotomosly branching stems emerged spore-bearing cones. The fact that they emerge from the growing tips of the branches suggests that each scale tree only got one shot at reproduction. Again, analyses of some fossilized scale tree forests suggests that these plants were monocarpic, meaning each plant died after a single reproductive event. In fact, fossilized remains of a scale tree forest in Illinois suggests that mass reproductive events may have been the standard for at least some species. Scale trees would all have established at around the same time, grown up together, and then reproduced and died en masse. Their death would have cleared the way for their developing offspring. What an experience that must have been for any insect flying around these ancient swamps.

The fossilized strobilus of a Lepidodendron. Photo by Verisimilus T licensed under the GNU Free Documentation License.

Compared to modern day angiosperms, the habits of the various scale trees may seem a bit inefficient. Nonetheless, this was an extremely successful lineage of plants. Scale trees were the dominant players of the warm, humid, equatorial swamps. However, their dominance on the landscape may have actually been their downfall. In fact, scale trees may have helped bring about an ice age that marked the end of the Carboniferous.

You see, while plants were busy experimenting with building ever taller, more complex anatomies using compounds such as cellulose and lignin, the fungal communities of that time had not yet figured out how to digest them. As these trees grew into 100 ft monsters and died, more and more carbon was being tied up in plant tissues that simply weren’t decomposing. This lack of decomposition is why we humans have had so much Carboniferous coal available to us. It also meant that tons of CO2, a potent greenhouse gas, were being pulled out of the atmosphere millennia after millennia.

A fossilized root or “stigmaria”. Photo by Verisimilus T licensed under CC BY-SA 3.0

As atmospheric CO2 levels plummeted and continents continued to shift, the climate was growing more and more seasonal. This was bad news for the scale trees. All evidence suggests that they were not capable of keeping up with the changes that they themselves had a big part in bringing about. By the end of the Carboniferous, Earth had dipped into an ice age. Earth’s new climate regime appeared to be too much for the scale trees to handle and they were driven to extinction. The world they left behind was primed and ready for new players. The Permian would see a whole new set of plants take over the land and would set the stage for even more terrestrial life to explode onto the scene.

It is amazing to think that we owe much of our industrialized society to scale trees whose leaves captured CO2 and turned it into usable carbon so many millions of years ago. It seems oddly fitting that, thanks to us, scale trees are once again changing Earth’s climate. As we continue to pump Carboniferous CO2 into our atmosphere, one must stop to ask themselves which dominant organisms are most at risk from all of this recent climate change?

Photo Credits: [1] [2] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

The Japanese Umbrella Pine

Photo by Dr. Scott Zona licensed under CC BY-NC 2.0

My first impression of the Japanese umbrella pine was that I was looking at a species of yew (Taxus spp.). Sure, its features were a bit more exaggerated than I was used to but what do I know? Trying to understand tree diversity is a recent development in my botanical obsession so I don’t have much to base my opinions on. Regardless, I am glad I gave the little sapling I was looking at a closer inspection. Turns out, the Japanese umbrella pine is most definitely not a yew. It is actually unique in its taxonomic position as the only member of the family Sciadopityaceae.

The Japanese umbrella pine goes by the scientific name of Sciadopitys verticillata. Both common and scientific names hint at the whorled arrangements of its “leaves.” I place leaves in quotes because they are not leaves at all. One of the most remarkable features of this tree is the fact that those whorled leaves are actually thickened, photosynthetic extensions of the stem known as “cladodes.”

Those tiny bumps along the stems are actually highly reduced leaves whereas the whorls of photosynthetic “leaves” are actually modified extensions of the stem called “cladodes.” Photo by Steven Severinghaus licensed under CC BY-NC-SA 2.0

Photo by KENPEI licensed under the GNU Free Documentation License.

Photo by James licensed under CC BY 2.0

It seems that the true leaves of the Japanese umbrella pine have, through evolutionary time, been reduced to tiny, brown scales that clasp the stems. I am not sure what evolutionary advantage(s) cladodes infer over leaves, however, at least one source suggested that cladodes may have fewer stomata and therefore can help to reduce water loss. Until someone looks deeper into this mystery, we cannot say for sure.

As a tree, the Japanese umbrella pine is slow growing. Records show that young trees can take upwards of a decade to reach average human height. However, given time, the Japanese umbrella pine can grow into an impressive specimen. In the forests of Japan, it is possible to come across trees that are 65 to 100 ft (20 – 35 m) tall. It was once wide spread throughout much of southern Japan, however, an ever-increasing human population has seen that range reduced.

A 49.5 million years old fossil of a Sciadopitys cladode. Photo by Kevmin licensed under CC BY-SA 3.0

The gradual reduction of this species is not solely the fault of humans. Fossil evidence shows that the genus Sciadopitys was once wide spread throughout parts of Europe and Asia as well. Whereas the current diversity of this genus is limited to a single species, fossils of at least three extinct species have been found in rocks dating back to the Triassic Period, some 230 million years ago. It would appear that this obscure conifer family, like so many other gymnosperm lineages, has been on the decline for quite some time.

Despite the obscure strangeness of the Japanese umbrella tree, it has gained considerable popularity as a unique landscape tree. Because it hails from a relatively cool regions of Japan, the Japanese umbrella tree adapts quite well to temperate climates around the globe. Enough people have grown this tree that some cultivars even exist. Whether you see it as a specimen in an arboretum or growing in the wild, know that you are looking at something quite special. The Japanese umbrella tree is a throwback to the days when gymnosperms were the dominant plants on the landscape and we are extremely lucky that it made it through to our time.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3]

Early Land Plants Made The World Muddy

Cooksonia is one of the earliest land plants to have evolved. Photo by Matteo De Stefano/MUSE licensed under CC BY-SA 3.0

Try to picture the world before life moved onto land. It would have been a vastly different landscape than anything we know today. For one, there would have been no soil. Before life moved onto land, there was nothing organic around to facilitate soil formation. This would have changed as terrestrial habitats were slowly colonized by microbes and eventually plants. A recent paper published in Science is one of the first to demonstrate that the rise in certain sediments on land, specifically mud-forming clays, coincided with the rise in deep-rooted land plants.

This was no small task. The research duo had to look at thousands of reports spanning from the Archean eon, some 3.5 billion years ago, to the Carboniferous period, some 358 million years ago. By looking for the relative amounts of a sedimentary rock called mudrock in terrestrial habitats, they were able to see how the geology of terrestrial habitats was changing through time. What they found was that the presence of mudrock increased by orders of magnitude around the same time as early land plants were beginning to colonize land. Before plants made it onto land, mudrocks comprised a mere 1% of terrestrial sediments. By the end of the Carboniferous period, mudrocks had risen to 26%.

This begs the question, why are mudrocks so significant? What do they tell us about what was going on in terrestrial environments? A key to these questions lies in the composition of mudrocks themselves. Mudrock is made up of fine grained sediments like clay. There are many mechanisms by which clay can be produced and certainly this was going on well before plants made it onto the scene. The difference here is in the quantity of clay-like minerals in these sediments. Whereas bacteria and fungi do facilitate the formation of clay minerals, they do so in small quantities.

A little bit of moss goes a long way for erosion control!

The real change came when plants began rooting themselves into the earth. In pushing their roots down into sediments, plants act as conduits for increased weathering of said minerals. Roots not only increase the connectivity between subsurface geology and the atmosphere, they also secrete substances like organic acids and form symbiotic relationships with cyanobacteria and fungi that accelerate the weather process. No purely tectonic or chemical processes can explain the rate of weathering that must have taken place to see such an increase in these fine grained minerals.

What's more, the presence of rooted plants on land would have ensured that these newly formed muds would have stuck around on the landscape much longer. Whereas in the absence of plants, these sediments would have been washed away into the oceans, plants were suddenly holding onto them. Plant roots act as binders, holding onto soil particles and preventing erosion. Aside from their roots, the rest of these early land plants would have also held onto sediments via a process known as the baffling effect. As water and wind pick up and move sediments, they inevitably become trapped in and around the stems and leaves of plants. Even tiny colonies of liverworts and moss are capable of doing this and entire mats of these would have contributed greatly to not only the formation of these sediments, but their retention as well.

The movement of plants onto land changed the course of history. It was the beginning of massive changes to come and much of that started with the gradual formation of soils. We owe everything to these early botanical pioneers.

Photo Credit: [1]

Further Reading: [1]

The First Trees Ripped Themselves Apart To Grow

Illustration by Falconaumanni licensed under CC BY-SA 3.0

A new set of fossil discoveries show that the evolutionary arms race that are forests started with plants that literally had to rip themselves apart in their battle for the canopy. The first forests on this planet arose some 385 million years ago and were unlike anything we know today. They consisted of a clade of trees known scientifically as Cladoxylopsids, which have no living representatives in these modern times. How these trees lived and grew has remained a mystery since their fossilized trunks were first discovered but a new set of fossils from China reveals that these trees were unique in more ways than one.

Laying eyes on a full grown Cladoxylopsid would be a strange experience to say the least. Their oddly swollen base would gradually taper up a trunk that stretched some 10 to 12 meters (~30 - 40 feet) into a canopy of its relatives. They had no leaves either. Instead, their photosynthetic organs consisted of branch-like growths that were covered in twig-like projections. Whereas most fossils revealed great detail about their outward appearance, we have largely been in the dark on what their internal anatomy was like. Excitingly, a set of exquisitely preserved fossils from Xinjiang, China has changed that. What they reveal about these early trees is quite remarkable.

[SOURCE]

As it turns out, the trunks of these early trees were hollow. Unlike the trees we know today, whose xylem expands in concentric rings and forms a solid trunk, the trunk of Cladoxylopsid was made up of strands of xylem connected by a network of softer tissues. Each of these strands was like a mini tree in and of itself. Each strand formed its own concentric rings that gradually increased the size of the trunk. However, this gradual expansion did not appear to be a gentle process.

As these strands increased in size, the trunk would grow larger and larger. In doing so, the tissues connecting the strands were pulled tighter and tighter. Eventually they would tear under the strain. They would gradually repair themselves over time but the effect on the trunk was quite remarkable. In effect, the base of the tree would literally collapse in on itself in a controlled manner. You could say that older Cladoxylopsids developed a bit of a muffin top at their base. 

A cross section of a Cladoxylopsid trunk showing the hollow center, individual xylem strands, and the network of connective tissues. [SOURCE]

Although this seems very detrimental, the overall structure of the tree would have been sturdy. The authors liken this to the design of the Eiffel tower. Indeed, a hollow cylinder is actually stronger than a solid one of the same dimensions. When looked at in the context of all other trees, this form of growth is truly unique. No other trees are constructed in such a manner.

The authors speculate that this form of growth may be why these trees eventually went extinct. It would have taken a lot of energy to grow in that manner. It is possible that, as more efficient forms of growth were evolving, the Cladoxylopsids may not have been able to compete. It is anyone's guess at this point but this certainly offers a window back into the early days of tree growth. It also shows that there has always been more than one way to grow a tree.

LEARN MORE ABOUT THESE TREES AND THE FORESTS THEY MADE IN EPISODE 253 OF THE IN DEFENSE OF PLANTS PODCAST.

Photo Credits: [1] [2]

Further Reading: [1]

The Ginkophytes Welcome a New Member

Despite their dominance on the landscape today, the evolutionary history of the major seed-bearing plant lineages is shrouded in mysteries. We simply don't have a complete picture of their evolution and diversification through time. Still, numerous fossils are turning up that are shedding light on some of these mysteries, including some amazingly well-preserved plant fossils from Mongolia. One set of fossils in particular is hinting that the part of the seed-bearing family tree that includes the Ginkgo was much more diverse in both members and forms.

The fossils in question were unearthed from the Tevshiin Govi Formation of Mongolia and date back to the Early Cretaceous period, some 100 to 125 million years ago. Although these fossils do not represent a newly discovered plant, their preservation is remarkable, allowing a much more complete understanding of what they were along with where they might sit on the family tree. The fossils themselves are lignified and have preserved, in extreme detail, fine-scale anatomical details that reveal their overall structure and function.

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The paleobotanical team responsible for their discovery and analysis determined that these were in fact seed-bearing cupules of a long-extinct Ginkgophyte, which they have named Umaltolepis. Previous discoveries have alluded to this as well, however, their exact morphology in relation to the entire organism has not always been clear. These new discoveries have revealed that the cupules (seed-bearing organs) themselves were borne on a stalk that sat at the tips of short shoots, very similar to the shoots of modern Ginkgo. They opened along four distinct slits, giving the structure an umbrella-like appearance.

The seeds themselves were likely wind dispersed, however, it is not entirely clear how fertilization would have been achieved. Based on similar analyses, it is very likely that this species was wind pollinated. Alongside the cupules were exquisitely preserved leaves. They were long, flat, and exhibit venation and resin ducts similar to that of the extant Ginkgo biloba. Taken together, these lines of evidence point to the fact that this group, currently represented by a single living species, was far more diverse during this time period. The differences in seed bearing structures and leaf morphology demonstrates that the Ginkgophytes were experimenting with a wide variety of life history characteristics.

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Records from across Asia show that this species and its relatives were once wide spread throughout the continent and likely inhabited a variety of habitat types. Umaltolepis in particular was a denizen of swampy habitats and shared its habitat with other gymnosperms such as ancient members of the families Pinaceae, Cupressaceae, and other archaic conifers. Because these swampy sediments preserved so much detail about this ecosystem, the team suggests that woody plant diversity was surprisingly low, having turned up fossil evidence for only 10 distinct species so far. Other non-seed plants from Tevshiin Govi include a filmy fern and a tiny moss, both of which were likely epiphytes.

Whereas this new Umaltolepis species represents just one player in the big picture of seed-plant evolution, it nonetheless a major step in our understanding of plant evolution. And, at the end of the day, fossil finds are always exciting. They allow us a window back in time that not only amazes but also helps us understand how and why life changes as it does. I look forward to more fossil discoveries like this.

LISTEN TO EP 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS DISCOVERY AND MORE!

*Thanks to Dr. Fabiany Herrera for his comments on this piece

Photo Credits: [1]

Further Reading: [1] [2]

Ferns Unchanged

Ferns are old. Arising during the late Devonian period, some 360 million years ago, ferns once dominated the land. These ancient ferns were a bit different than the ferns we know today. It wasn't until roughly 145 million years ago, during the late Cretaceous period, that many extant fern families started to appear. However, a recent fossil discovery shows that at least one familiar fern was hanging out with dinosaurs as far back as 180 million years ago!

A team of scientists in Sweden recently unearthed an exquisitely preserve fossil of a fern from some early Jurassic deposits. Usually the fossilization process does not preserve very fine details, especially not at the cellular level, but that is not the case for this fossil. Falling into volcanic hydrothermal brine, the fern quickly mineralized. The speed at which the tissues of the fern were replaced by minerals preserved details that paleontologists usually only dream about. Clearly visible in the fossilized stem are subcellular structures like nuclei and even chromosomes in various stages of cell division!

 

A) Section of the fossil rhizome. B-J) Exquisitely preserve cellular details [SOURCE]

Using sophisticated microscopy techniques, the team was able to analyze the properties of the nuclei undergoing division. What they discovered is simply amazing. The number of chromosomes as well as other properties of the DNA matched a fern that is quite common in eastern North America and Asia today. This fossilized fern, as far as the team can tell, is a close relative of the cinnamon fern (Osmundastrum cinnamomeum), placing it in the royal fern family (Osmundaceae). Based on the fossil evidence, relatives of these ferns were not only around during the early Jurassic, they have remained virtually unchanged for 180 million years. Talk about living fossils!

Further Reading: [1] [2]

Tomatillos Just Got A Lot Older

Photo by Ignacio Escapa, Museo Paleontológico Egidio Feruglio

Tomatillos and ground cherries just got a bit older. Okay, a lot older. Exquisitely preserved fossils from an ancient lake bed in Argentina are shining a very bright light on the genus Physalis and the family Solanaceae as a whole. Despite the importance of this plant family around the globe, little fossil evidence has ever been found. That is, until now. 

Dated at 52 million years old, these fossils paint a picture of a snapshot in the evolution of the genus Physalis. The fossils are remarkable, allowing for close inspection of minute details like vein structure. Because of the level of detail discernible, experts can say without a doubt that these fossils could be nothing else other than a species of Physalis. 

One of the most interesting aspects of these fossils is their age. These sediments were deposited during the early Eocene Epoch. The fact that representatives of Physalis were alive and well during this time is quite remarkable. Because fossil evidence for Solanaceae has been so scarce, experts have had to rely solely on molecular dating in order to elucidate the origin and divergence of this family. 

Original estimates placed the origin of Solanaceae at sometime around 30 million years before present. Physalis, being much more derived, was thought to have an even more recent emergence, some 9 million years ago. Boy, was that ever wrong. At 52 million years of age, we can now confidently say that Physalis is at least 43 million years older than previously thought. These findings also tell us that Solanaceae is even older still! If such a derived genus was thriving in Eocene Argentina 52 million years ago, basil members of the family must have gotten their start much earlier than we ever imagined. 

Aside from big picture taxonomical revelations, the fossils also give us a window into the ecology of these ancient Physalis. The most obvious is that inflated bladder which surrounds the berry within. Though it is quite characteristic of this group, little attention has been paid to its function. The fact that the sediments in which they were preserved are of aquatic origin suggests that the inflated calyces may have evolved for aquatic seed dispersal. Experiments have shown that these structures on modern day ground cherries and tomatillos do in fact float, keeping the berry inside high and dry. 

To think that all of this was brought to light from a handful of fossils. It just goes to show you the importance the paleontological discoveries can have. Just think of the countless amount of museum drawers and shelves that are chock full of interesting fossils waiting to be looked over. Who knows what they might tell us about our planet. 

Photo Credit: Ignacio Escapa, Museo Paleontológico Egidio Feruglio

Further Reading: [1]

"The Ghosts of Cultivation Past"

Photograph © Andrew Dunn, 13 September 2005. Website: http://www.andrewdunnphoto.com/ licensed under CC BY-SA 2.0

All too often we think of a species' niche as a sort of address. Species will be present in suitable habitat and absent from unsuitable habitat. Certainly this oversimplification has been useful to us, however, it often ignores context. Species, especially long lived ones, can often be found in unsuitable habitat. Similarly, biotic interactions such as pollinators and seed dispersers are regularly overlooked when considering "suitable habitat." The absence of factors such as this can leave plants stranded in suboptimal conditions. 

A recent paper published in PLOS One tackles this very idea by looking at a species of tree many of us will be familiar with - the honey locust (Gleditsia triacanthos). This central North American legume is widely planted as a street/landscape tree all over the United States. Ecologically speaking, honey locusts can be found growing wild in open xeric upland sites. In places like the southern Appalachian Mountains, however, they can also be found growing in mesic bottomlands. Regardless of where it is found, the honey locust seems to be severely dispersal limited (except in cases where cattle and other livestock have been introduced). 

Before modern times, honey locust likely relied on Pleistocene megafauna to get around. The end of the Pleistocene marked the end of these large mammals. Left behind were many different plant species that had evolved alongside them. For a small handful of these plants, humans were a saving grace. Such is the case for the honey locust. Inside the honey locust pods there is a sugary pulp, which in southern Appalachia, the Cherokee were quite fond of. The Cherokee also used the tree for making weapons and gamesticks. As such, the honey locust holds great cultural significance, so much so that the Cherokee named at least one settlement "Kulsetsiyi" (more commonly known today as Cullasaja), which translates to "honey locust place." 

Author, Dr. Robert Warren, noticed that in southern Appalachia, "Every time I saw a honey locust, I could throw a rock and hit an archaeological site.” What's more, the trees were not recruiting well unless cattle or some other form of human disturbance was present. This species seemed to be a prime candidate for testing persistent legacy effects in tree distributions. 

Using seed germination experiments and lots of mapping, Dr. Warren was able to demonstrate that honey locust distributions in the southern Appalachian region are more closely tied to Cherokee settlements than its own niche requirements. The germination experiments strengthened this correlation by showing that mesic bottomlands had the lowest germination and survival rates. 

Additionally, these sites are well known as former sites of Cherokee settlement and agriculture. Because this tree held such significance to their culture, it is quite likely that in lieu of Pleistocene megafauna, Native Americans, and eventually European livestock, allowed the honey locust to reclaim some of its former glory. Of course, today it is a staple of horticulture. Still, the point is that despite being found growing in a variety of habitat types, the honey locust is very often found in unsuitable habitat where it cannot reproduce without a helping hand. In the southern Appalachian region, honey locust distributions are more a reflection of Native American cultural practices.

Photo Credit: Cambridge Botanic Garden

Further Reading:
http://bit.ly/27SySpq

Paleo Pinus

Photo Credit: Howard Falcon-Lang, Royal Holloway University of London

What you are looking at here is the oldest fossil evidence of the genus Pinus. Now, conifers have been around a long time. I mean really long. Recognizable members of this group first came onto the scene sometime during the late Triassic, some 235 million years ago. Today, one of the most species-rich genera of conifers are those in the genus Pinus. They dominate northern hemisphere forests and can be found growing in dry soils throughout the globe. For such a commonly encountered group, their origins have remained a bit of a mystery. 

The fossil was discovered in Nova Scotia, Canada. Unlike the rocky fossils we normally think of, this fossil was preserved as charcoal, undoubtedly thanks to a forest fire. The degree of preservation in this charcoal specimen is astounding and provides ample opportunity for close investigation. 

I mentioned that this fossil is old. Indeed it is. It dates back roughly 133 –140 million years, which places it in the lower Cretaceous. What is remarkable is that it predates the previous record holder by something like 11 million years. Even more remarkable, however, is what this tiny fossil can tell us about the ecology of Pinus at that time. 

Firstly, the leaf scars indicate that this tree had two needles per fascicle. This implies that the genus Pinus had already undergone quite the adaptive radiation by this time. If this is the case, it pushes back the clock on pine evolution even earlier. Another interesting feature are the presence of resin ducts. In extant species, these ducts secrete highly flammable terpenes, which would have potentially promoted fire. 

Species that exhibit this morphology today often utilize an ecology that promotes devastating crown fires that clear the land of competition for their seedlings. Although more evidence is needed to confirm this, it nonetheless suggests that such fire adaptations in pines were already shaping the landscape of the Cretaceous period. All in all, this fossil is a reminder that big things often come in small packages. 

Photo Credit: Howard Falcon-Lang, Royal Holloway University of London

Further Reading:

http://bit.ly/1QP85zm

A Flower Trapped in Amber

Photo by George Poinar [SOURCE]

Thanks to a 30 year old collection of amber tucked away in the drawers of a museum, we now have the first fossil record of the asterid lineage. Discovered in the Dominican Republic back in 1986, this particular chunk of amber contains a tiny flower about a centimeter in length. The preservation is astounding, allowing researchers to accurately identify this as a member of the genus Strychnos.

The asterid lineage contains many orders that we would be familiar with including Gentianales, Lamiales and Solanales. It is highly derived yet poorly represented in the fossil record. Because of the challenges associated with accurately dating amber, scientists estimate that this flower is somewhere between 15 - 45 million years old. To put this in perspective, North and South America were not even connected at this point in time. What's more, the details preserved in these amber deposits are allowing researchers to piece together what the forest in this region would have looked like.

These fossils show that this forest "contained a distinct canopy layer composed of legumes such as algarroba (Hymenaea protera), cativo (Prioria spp.) and nazareno (Peltogyne spp.), with emergent trees like caoba (Swietenia; Meliaceae) extending through the canopy. The subcanopy and understory were represented by royal palms (Roystonea) and figs (Ficus; Moraceae). The shrub layer included other types of palms as well as acacias. Grasses like pega-lega (Pharus) and bambusoids (Alarista) colonized the forest floor. Orchids, bromeliads, ferns and vines covered the trees, and various lianas were also part of this tropical forest."

Pretty amazing for bits and pieces of solidified tree sap. This particular flower has been named Strychnos electri, a now extinct species. However, the morphological characteristics show that this particular genus as well as the asterid lineage were already well established at this time. Discoveries such as this are offering highly detailed windows into the past, which allows us to better understand flowering plant evolution and ecosystem change.

Photo Credit: George Poinar

Further Reading:
http://www.nature.com/articles/nplants20165

Cretaceous Seeds Shine Light on the Evolution of Flowering Plants

What you are looking at here are some of the earliest fossil remains of flowering plants. These seeds were preserved in Cretaceous sediments dating back some 125–110 million years ago. Fossil evidence dating to the early days of the angiosperm lineage is scant, which makes these fossils all the more spectacular. Thanks to a large collaborative effort, Dr. Else Marie Friis is shining light on the evolution of seeds.

Finding these fossils is not a matter of seeing them with the naked eye. These seeds are tiny, ranging from half a millimeter up to 2 millimeters in length. They were discovered using an advanced form of X-ray microscopy. The advantage of this technique is not only that it is nondestructive but it also allows researchers to investigate the internal structures of the seeds that would otherwise be impossible to see. Their preservation is mind blowingly delicate, allowing researchers to see minute details of the embryo and even subcellular structures like nuclei. 

Dr. Friis' team was able to look at over 250 fossil seeds from 75 different taxa. They were able to make 3D models of the embryos, allowing for more detailed studies than ever before. For some of the fossils, the detail was such that they were able to match them to extant lineages of flowering plants. For others, this technique is allowing for better reclassification of now extinct species. 

By far the most exciting part about these fossils are what they can tell us about the ecology of early flowering plants. In all instances, the embryos within the seeds were small, immature, and dormant. This suggests that seed dormancy is a fundamental trait of flowering plants. What's more, this lends support to the hypothesis that angiosperms first evolved as opportunistic, early successional colonizers. Seed dormancy allows flowering plants to wait out the bad times until favorable environmental conditions allowed for germination and seedling establishment. 

Photo Credit: Dr. Else Marie Friis

Further Reading:
http://www.nature.com/nature/journal/v528/n7583/full/nature16441.html

Germinating a Seed After 32,000 Years

[SOURCE]

What you are looking at are plants that were grown from seeds buried in permafrost for nearly 32,000 years. The seeds were discovered on the banks of the Kolyma River in Siberia. The river is constantly eroding into the permafrost and uncovering frozen Pleistocene relics. Upon their discovery, researchers took the seeds and did the unthinkable - they grew them into adult plants. To date, this is the oldest resurrected plant material. 

The key to their extreme longevity lies in the permafrost. They were found inside the frozen burrow of an Arctic ground squirrel. The state of the burrow suggests that everything froze quite rapidly. As such, the seeds remained in a state of suspended animation for 32,000 years. This is not the first time viable plant materials have been recovered from Pleistocene permafrost. Spores, mosses, as well as seeds of other flowering plants have been rejuvenated to some degree in the past but none of these were grown to maturity. 

Using micropropagation techniques coupled with tissue cultures, researchers were able to grow and flower the 32,000 year old seeds. What they discovered was that these seeds belonged to a plant that can still be found in the Arctic today. It is a small species in the family Caryophyllaceae called Silene stenophylla. However, there were some interesting differences. 

As it turns out, the seeds taken from the burrow proved to be a phenotype quite distinct from extant S. stenophylla populations. For instance, their flowers were thinner and less dissected than extant populations. Also, whereas the flowers of extant populations are all bisexual, individuals grown from the ancient seeds first produced only female flowers followed by fewer bisexual flowers towards the end of their blooming period.Though there are many possible reasons for this, it certainly hints at the different environmental parameters faced by this species through time. What's more, such findings allow us a unique window into the world of seed dormancy. Researchers are now looking at such cases to better inform how we can preserve seeds for longer periods of time. 

Photo Credit: Svetlana Yashinaa, Stanislav Gubin, Stanislav Maksimovich, Alexandra Yashina, Edith Gakhova, and David Gilichinsky

Further Reading: [1]

Aquatic Angiosperm: A Cretaceous Origin?

Via Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro [SOURCE]

It would seem that yet another piece of the evolutionary puzzle that are flowering plants has been found. I have discussed the paleontological debate centered around the angiosperm lineage in the past (http://bit.ly/1S6WLkf), and I don't think the recent news will put any of it to rest. However, I do think it serves to expand our limited view into the history of flowering plant evolution.

Meet Montsechia vidalii, an extinct species that offers tantalizing evidence that flowering plants were kicking around some 130–125 million years ago, during the early days of the Cretaceous. It is by no means showy and I myself would have a hard time distinguishing its reproductive structures as flowers yet that is indeed what they are thought to be. Detailed (and I mean detailed) analyses of over 1,000 fossilized specimens reveals that the seeds are enclosed in tissue, a true hallmark of the angiosperm lineage.

On top of this feature, the fossils also offer clues to the kind of habitat Montsechia would have been found in. As it turns out, this was an aquatic species. The flowers, instead of poking above the water, would have remained submerged. An opening at the top of each flower would have allowed pollen to float inside for fertilization. Another interesting feature of Montsechia is that it had no roots. Instead, it likely floated around in shallow water.

Via Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro [SOURCE]

This is all very similar to another group of extant aquatic flowering plants in the genus Ceratophyllum (often called hornworts or coon's tail). Based on such morphological evidence, it has been agreed that these two groups represent early stem lineages of the angiosperm tree. Coupled with what we now know about the habitat of Archaefructus (http://bit.ly/1S6WLkf), it is becoming evident that the evolution of flowers may have happened in and around water. This in turn brings up many more questions regarding the selective pressures that led to flowers.

What is even more amazing is that these fossils are by no means recent discoveries. They were part of a collection that was excavated in Spain over 100 years ago. Discoveries like this happen all the time. Someone finds a interesting set of fossils that are then stored away on a dark shelf in the bowels of a museum only to be rediscovered decades or even centuries later.

All in all I think this discovery lends credence to the idea that flowering plants are a bit older than we like to think. Also, one should be wary of anyone claiming to have found "the first flower." The idea that there could be a fossil out there that depicts the first anything is flawed a leads to a lot of confusion. Instead, fossils like these represent snapshots in the continuum that is evolution. Each new discovery reveals a little bit more about the evolution of that lineage. We will never find the first flower but we will continue to refine our understanding of life on this planet.

Photo Credits: Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro,

Further Reading:
http://www.pnas.org/content/112/35/10985.abstract

Southern Tundra

One would hardly consider the southern half of North America to be a tundra-like environment but even so, some tundra plants exist there today...

Up until about 11,000 years ago, much of North America was covered in massive glaciers that were, in some places, upwards of a mile thick. These colossal ice sheets scoured the land over millennia as they advanced and retreated throughout the Pleistocene. Where they covered the land, nothing except some mosses survived. A vast majority of plants were either wiped out or were forced to survive in what are referred to as glacial refugia.

Refugia are ice free areas either within the range of the ice sheets, such as mountain tops, or areas just outside of the ice sheets. Many of North America's plant species took refuge to the south of the glaciers in what is now the Appalachian Mountains. Echos of these plant communities still exist in the southern US today. Some of which are quite isolated from the current distribution of their species. These plant communities are considered disjunct and coming across them is like seeing back in time.

One such plant is the three-toothed cinquefoil (Sibbaldiopsis tridentata). This species is mainly found in northern Canada and Greenland and is considered a tundra species. It needs cold temperatures and is easily out competed in all but the most hostile environments. Why then can you find this lovely cinquefoil growing as far south as Georgia?

The answer are mountains. A combination of high elevation, punishing winds, and lower than average temperatures, means that the peaks of the Appalachian Mountains have more in common with the tundras found much farther north on the continent. As a result of these conditions, plants like S. tridentata have been able to survive into the present while the majority of their tundra associates migrated north with the retreat of the glaciers.

Because of their isolated existence in the Appalachians, S. tridentata is considered endangered in many southern states. Being able to see this plant without having to visit the tundra is quite a unique and humbling experience. It is amazing to consider the series of events that, over thousands of years, have caused this species to end up living on top of these mountains. It is one of those things that one must really stop and mull over for a bit in order to fully appreciate.

Further Reading:
http://plants.usda.gov/core/profile?symbol=sitr3

http://onlinelibrary.wiley.com/…/j.1365-2699.1998.…/abstract

http://www.castaneajournal.org/doi/abs/10.2179/10-039.1

http://instaar.colorado.edu/AW/abstract_details.php?abstract_id=16