A Pair of Cycads Aim to Reproduce in the UK for the First Time in 120 Million Years

Photo by Danorton licensed by CC BY-SA 4.0

We tend to speak in the future tense when it comes to climate change. Phrases like "climate change will alter..." and "species will be affected by climate change..." suggest that these are issues we will eventually face at some point down the road. In reality, climate change is happening and life is already responding. Plants are some of the best indicators that thing are and have been changing since humans started wreaking havoc on natural systems.

Even in the most remote corners of our planet, where human presence is almost nil, we are finding evidence of climate change in the flora. For instance, deep in the Andes Mountains, trees are already adjusting their ranges to cope with changes in regional climate. And now, cycads are reproducing outdoors in the UK for the first time since dinosaurs walked the Earth.

Sago palms (Cycas revoluta) are native to parts of southern Japan and though they can handle frosts, they require mild winters and hot summers to successfully reproduce. A few decades ago, one would have a hard time trying to overwinter these cycads outdoors in the UK but the climate has been changing. Today, these plants can be successfully grown outdoors in the southern portion of the country provided they are given a little bit of shelter. Though they will grow well in such situations, convincing these plants to reproduce is another matter entirely.

The UK is no stranger to the effects of climate change. For instance, the plants in question are growing in the Ventnor Botanic Garden on the Isle of Wight where even today’s lowest temperatures are significantly hotter than even the hottest recorded temperatures on the island 100 years ago. The plants are responding accordingly.

For the first time in UK’s human history, both male and female sago palm cycads are producing cones at the same time outdoors. This means that cycads will be able to successfully reproduce at this latitude since at least the Cretaceous Period, roughly 120 million years ago. During the Cretaceous, distant cousins of these cycads could be found growing in what today is the UK. At that time, Earth’s atmosphere was chock full of CO2 and quite hot. The fact that cycads are once again able to reproduce in the UK is alarming to say the least. It is a forecast of more changes to come.

UPDATE: Thanks to Dr. Susannah Lyndon and Robbie Blackhall-Miles for bringing to my attention that this is actually not this first time this has happened in the UK. Apparently Sago palm cycads have produced cones in places like London in recent history. Nonetheless, such events are evidence of a warming climate.

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Further Reading: [1] [2]

Surprising Genetic Diversity in Old Growth Trees

Photo by S. Rae licensed by CC BY 2.0

Long-lived trees face a lot of challenges throughout their lives. Many trees can live for centuries, which can be a problem because plants cannot get up and move when conditions become unfavorable. This should equate to a slower rates of adaptation and evolution for long lived trees but that isn’t always the case. Many trees are often superbly capable of adapting to local conditions. Recently, a team of researchers from the University of British Columbia have provided some insights into the genetic mechanisms that may underpin such adaptive potential.

Genetic insights came from a species of conifer many will be familiar with - the Sitka spruce (Picea sitchensis). Researchers were interested in these trees because they live for a long time (upwards of 500 years or more) and can grow to heights of over 70 meters (230 ft.). They wanted to understand how genetic mutations work in trees like the Sitka spruce because plants are doing things a bit different than animals in that department.

Plants are modular organisms, meaning they grow by producing multiple copies of discrete units. This equates to a branching structure whose overall shape is in large part determined by environmental influences. It also means that when genetic mutations occur in one branch, they can be carried on throughout the growth of those tissues independent of what is going on throughout the rest of the plant. This means that older trees can often accumulate a surprising amount of genetic diversity throughout the entire body of the plant.

Photo by Brandon Kuschel licensed by Creative Commons Attribution 3.0 Unported

When researchers sampled the DNA of tissues from the trunks and the needles of tall, old growth Sitka spruce, they were shocked by what they had found. From the base of the tree to the needles in the canopy, an old growth Sitka spruce can show as much as 100,000 genetic differences. That is a lot of genetic diversity for a single organism. Though plenty of other trees have been found to exhibit varying levels of genetic differences within individuals, this is one of the highest mutation rates ever found in a single eukaryotic organism. This could also explain why such long-lived organisms can survive in a changing world for their entire lives.

Now, it is important to note that many mutations are likely either neutral or potentially harmful. Also, the rates of mutation may differ depending on where you look on this tree. For instance, needles at the top of a Sitka spruce are going to be exposed to far more gene-altering UV radiation than bark tissues near the base. Still, over the lifetime of a single tree, rare beneficial mutations can and do accumulate. Imagine a scenario in which one branch mutation results in needles that are more resistant to say an insect pest. Those needles could hypothetically receive less damage than needles elsewhere on the tree. This odd form of selection is occurring within the lifetime of that tree and may even have implications for the future offspring of that tree thanks again to the quirks of how tree reproductive cells develop.

Many trees also do not have segregated germlines. What this means is that unlike animals whose reproductive cells develop from separate cell lineages than the rest of their body cells, the reproductive cells of trees develop from somatic cells, which are the same cells that form stems, leaves, and branches. This means that if a mutation occurs on the germline of a branch that eventually goes on to produce cones, these mutations can be passed on in the seeds of those cones. This obviously needs a lot of evidence to substantiate but now that a mechanism is in place, we know where and what to look for.

Photo Credits: [1] [2]

Further Reading: [1] [2]

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 Celery-Topped Conifers

Photo by RTBG licensed under CC BY-NC-SA 2.0

I am only just starting to fully appreciate the diversity in form and habit exhibited by the gymnosperm lineages alive today. What I once thought of as a unidimensional group of plants is proving to be wonderfully diverse, despite being overshadowed by the angiosperms. For instance, imagine my surprise when I first laid eyes on a member of the genus Phyllocladus.

At first glance, these weird conifers look more like a broad-leaf angiosperm. This similarity is superficial, of course. Before we get to why they look the way they do, it is worth considering this group from a as a whole. The genus Phyllocladus comprises roughly 5 species spread out among New Zealand, Tasmania, and Malesia. They are somewhat variable in form but usually settle out somewhere between a good sized shrub and a medium sized tree. Where exactly this genus of oddball gymnosperms fits on the tree of life is subject to some debate.

Phyllocladus trichomanoides licensed under public domain

For many years after its initial description, Phyllocladus was placed in a family of its own - Phyllocladaceae. Subsequent molecular work has only managed to add to the confusion. Despite its unique morphological characteristics, some authors feel this genus fits nicely into the family Podocarpaceae. At least one other study suggests that it doesn’t belong in Podocarpaceae but rather is situated as sister to the family. By the looks of it, this will not be cleared up any time soon. So, for now, let’s focus in on why these plants are so strange.

For starters we have the “leaves.” I place the word ‘leaves’ in quotes because they are not true leaves. The correct term for these structures are phylloclades (hence the generic name). A phylloclade is a flattened projection of a branch that takes on the form and function of a leaf. What we know of as leaves have been greatly reduced in the genus Phyllocladus. If you want to see them, you must look closely at the tips of the phylloclades. Early on in their development, the leaves exist as tiny brown scales. These scales are gradually lost over time as they serve no function for the plant.

Phyllocladus alpinus. Photo by MurielBendel licensed under CC BY-SA 4.0

Though no one has tested this directly (that I am aware of), the evolution of phylloclades over leaves likely has to do with energy conservation in one form or another. Why produce stems and leaves when you can co-opt stem-like structures to do the work for you? Oddly enough, some suggest that to consider them stems in the truest sense of the word is erroneous. Morphologically speaking, they share traits that are intermediate between branches and stems. However, I am going to need to do more homework before I feel comfortable elaborating on this point.

Only when it comes time for reproduction does their place among the gymnosperms become readily apparent, that is before the ovules are fertilized. All members of the genus Phyllocladus produce cones. Male cones are tiny, cylindrical structures located at the ends of their side branches whereas female cones are clustered into groups along the axils or margins of the phylloclades. Once fertilized, however, these plants offer another point of confusion for the casual observer.

Phyllocladus is yet another genus of conifers that has converged on a fruit-like seed dispersal strategy. As the seed cones mature, the scales gradually swell and become berry-like. Poking out of the bright red and/or white aril is a single seed. These fleshy arils function in a similar way to fruit in that they attract birds, which then consume them, dispersing the seeds later on in their feces.

Another intriguing aspect of their morphology occurs below ground. The roots of this genus form nodules, which provide a home for bacteria that specializing in fixing atmospheric nitrogen. In return for a home and some carbohydrates from photosynthesis, these bacteria pay these trees with nitrogen that would otherwise be unavailable. Pretty remarkable stuff for a such an esoteric group of conifers!

Photo Credits: [1] [2]

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

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]

Gymnosperms and Fleshy "Fruits"

Fleshy red aril surrounding the seeds of Taxus baccata. Photo by Frank Vincentz licensed under the GNU Free Documentation License.

Many of us were taught in school that one of the key distinguishing features between gymnosperms and angiosperms is the production of fruit. Fruit, by definition, is a structure formed from the ovary of a flowering plant. Gymnosperms, on the other hand, do not enclose their ovules in ovaries. Instead, their unfertilized ovules are exposed (to one degree or another) to the environment. The word “gymnosperm” reflects this as it is Greek for “naked seed.” However, as is the case with all things biological, there are exceptions to nearly every rule. There are gymnosperms on this planet that produce structures that function quite similar to fruits.

Internal anatomy of a Ginkgo ovule with red arrow showing the integument.

Photo copyright Bruce Kirchoff, Licensed under CC BY 2.0

The key to understanding this evolutionary convergence lies in understanding the benefits of fruits in the first place. Fruits are all about packing seeds into structures that appeal to the palates of various types of animals who then eat said fruits. Once consumed, the animals digest the fruity bits and will often deposit the seeds elsewhere in their feces. Propagule dispersal is key to the success of plants as it allows them to not only to complete their reproductive cycle but also conquer new territory in the process. With a basic introduction out of the way, let’s get back to gymnosperms.

“Fruits” of Cephalotaxus fortunei (Cephalotaxaceae)

There are 4 major gymnosperm lineages on this planet - the Ginkgo, cycads, gnetophytes, and conifers. Each one of these groups contains members that produce fleshy structures around their seeds. However, their “fruits” do not all develop in the same way. The most remarkable thing to me is that, from a developmental standpoint, each lineage has evolved its own pathway for “fruit” production.

Ginkgo “fruits” are full of butyric acid and smell like rotting butter or vomit. Photo by H. Zell licensed under CC BY-SA 3.0

For instance, consider ginkgos and cycads. Both of these groups can trace their evolutionary history back to the early Permian, some 270 - 280 million years ago, long before flowering plants came onto the scene. Both surround their developing seed with a layer of protective tissue called the integument. As the seed develops, the integument swells and becomes quite fleshy. In the case of Ginkgo, the integument is rich in a compound called butyric acid, which give them their characteristic rotten butter smell. No one can say for sure who this nasty odor originally evolved to attract but it likely has something to do with seed dispersal. Modern day carnivores seem to be especially fond of Ginkgo “fruits,” which would suggest that some bygone carnivore may have been the main seed disperser for these trees.

“Fruits” contained within the female cone of a cycad (Lepidozamia peroffskyana). Photo by Tony Rodd licensed under CC BY-NC-SA 2.0

The Gnetophytes are represented by three extant lineages (Gnetaceae, Welwitschiaceae, and Ephedraceae), but only two of them - Gnetaceae and Ephedraceae - produce fruit-like structures. As if the overall appearance of the various Gnetum species didn’t make you question your assumptions of what a gymnosperm should look like, its seeds certainly will. They are downright berry-like!

Berry-like seeds of Gnetum gnemon. Photo by gbohne licensed under CC BY-SA 2.0

The formation of the fruit-like structure surrounding each seed can be traced back to tiny bracts at the base of the ovule. After fertilization, these bracts grow up and around the seed and swell to become red and fleshy. As you can imagine, Gnetum “fruits” are a real hit with animals. In the case of some Ephedra, the “fruit” is also derived from much larger bracts that surround the ovule. These bracts are more leaf-like at the start than those of their Gnetum cousins but their development and function is much the same.

Red, fleshy bracts of Ephedra distachya. Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

Whereas we usually think of woody cones when we think of conifers, there are many species within this lineage that also have converged on fleshy structures surrounding their seeds. Probably the most famous and widely recognized example of this can be seen in the yews (Taxus spp.). Ovules are presented singly and each is subtended by a small stalk called a peduncle. Once fertilized, a group of cells on the peduncle begin to grow and differentiate. They gradually swell and engulf the seed, forming a bright red, fleshy structure called an “aril.” Arils are magnificent seed dispersal devices as birds absolutely relish them. The seed within is quite toxic so it usually escapes the process unharmed and with any luck is deposited far away from the parent plant.

The berry-like cones of Juniperus communis. Photo by Piero Amorati, ICCroce - Casalecchio di Reno, Bugwood.org licensed under Creative Commons Attribution 3.0 License.

Another great example of fleshy conifer “fruits” can be seen in the junipers (Juniperus spp.). Unlike the other gymnosperms mentioned here, the junipers do produce cones. However, unlike pine cones, the scales of juniper cones do not open to release the seeds inside. Instead, they swell shut and each scale becomes quite fleshy. Juniper cones aren’t red like we have seen in other lineages but they certainly garnish the attention of many a small animal looking for food.

I have only begun to scratch the surface of the fruit-like structures in gymnosperms. There is plenty of literary fodder out there for those of you who love to read about developmental biology and evolution. It is a fascinating world to uncover. More importantly, I think the fleshy “fruits” of the various gymnosperm lineages stand as a testament to the power of natural selection as a driving force for evolution on our planet. It is amazing that such distantly related plants have converged on similar seed dispersal mechanisms by so many different means.

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3] [4] [5] [6] [7]

The Tecate Cypress: A Tree Left Hanging in the Balance

Photo by Anthonysthwd licensed under CC BY-SA 4.0

The tecate cypress is a relict. Its tiny geographic distribution encompasses a handful of sights in southern California and northwestern Mexico. It is a holdover from a time when this region was much cooler and wetter than it is today. It owes its survival and persistence to a combination of toxic soils, a proper microclimate, and fires that burn through every 30 to 40 years. However, things are changing for the Tecate cypress and they are changing fast. The fires that once ushered in new life for isolated populations of this tree are now so intense that they may spell disaster.

The taxonomy of the Tecate cypress has undergone a few revisions since it was first described. Early work on this species suggested it was simply a variety of Cupressus guadalupensis. Subsequent genetic testing revealed that these two trees were distinct enough to each warrant species status of their own. It was then given the name Cupressus forbesii, which will probably be familiar to most folks who know it well. Work done on the Tecate cypress back in 2012 has seen it moved out of the genus Cupressus and into the genus Hesperocyparis. As far as I am concerned, whether you call it Cupressus forbesii or Hesperocyparis forbesii matters not at this point.

The Tecate cypress is an edaphic endemic meaning it is found growing only on specific soil types in this little corner of the continent. It appears to prefer soils derived from ultramafic rock. The presence of high levels of heavy metals and low levels of important nutrients such and potassium and nitrogen make such soils extremely inhospitable to most plants. As such, the Tecate cypress experiences little competition from its botanical neighbors. It also means that populations of this tree are relatively small and isolated from one another.

Photo by Stan Shebs licensed under CC BY-SA 3.0

The Tecate cypress also relies on fire for reproduction. Its tiny cones are serotinous, meaning they only open and release seeds in response to a specific environmental trigger. In this case, it’s the heat of a wildfire. Fire frees up the landscape of competition for the tiny Tecate cypress seedlings. After a low intensity fire, literally thousands of Tecate cypress seedlings can germinate. Even if the parent trees burn to a crisp, the next generation is there, ready to take their place.

At least this is how it has happened historically. Much has changed in recent decades and the survival of these isolated Tecate cypress populations hangs in the balance. Fires that once gave life are now taking it. You see, decades of fire suppression have changed that way fire behaves in this system. With so much dry fuel laying around, fires burn at a higher intensity than they have in the past. What's more, fires sweep through much more frequently today than they have in the past due in large part to longer and longer droughts.

Photo by Stan Shebs licensed under CC BY-SA 3.0

Taken together, this can spell disaster for small, isolated Tecate cypress populations. Even if thousands of seedlings germinate and begin to grow, the likelihood of another fire sweeping through within a few years is much higher today. Small seedlings are not well suited to cope with such intense wildfires and an entire generation can be killed in a single blaze. This is troubling when you consider the age distributions of most Tecate cypress stands. When you walk into a stand of these trees, you will quickly realize that all are of roughly the same age. This is likely due to the fact that they all germinated at the same time following a previous fire event.

If all reproductive individuals come from the same germination event and wildfires are now killing adults and seedlings alike, then there is serious cause for concern. Additionally, when we lose populations of Tecate cypress, we are losing much more than just the trees. As with any plant, these trees fit into the local ecology no matter how sparse they are on the landscape. At least one species of butterfly, the rare Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress. Without this tree, their larvae have nothing to feed on.

Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress. Photo by USFWS Pacific Southwest Region licensed under CC BY 2.0

Although things in the wild seem uncertain for the Tecate cypress, there is reason for hope. Its lovely appearance and form coupled with its unique ecology has led to the Tecate cypress being something of a horticultural curiosity in the state of California. Seeds are easy enough to germinate provided you can get them out of the cones and the trees seem to do quite well in cultivation provided competition is kept to a minimum. In fact, specimen trees seem to adapt quite nicely to California's cool, humid coastal climate. Though the future of this wonderful endemic is without a doubt uncertain, hope lies in those who care enough to grow and cultivate this species. Better management practices regarding fire and invasive species, seed collection, and a bit more public awareness may be just what this species needs.

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

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

Gnetum Are Neat!

Photo by gbohne licensed under CC BY-SA 2.0

As much as I hate to admit it, when I think of gymnosperms my mind autopilots to conifers and ginkgos. I too easily forget about some of the other extant gymnosperm lineages with which we share space on this planet. Whereas one can easily pick out a conifer or a ginkgo from a lineup, some of the other gymnosperms aren't readily recognized as such. One group in particular challenges my gymnosperm search image to the extreme. I am, of course, talking about a family of gymnosperms known as Gnetaceae.

Gnetaceae is home to a single genus, Gnetum, of which there are about 40 species. They can be found growing in tropical forests throughout South America, Africa, and Southeast Asia. Gnetum essentially come in two forms, small trees and larger, scrambling vines. To most passersby, the various Gnetum species appear to be yet another tropical angiosperm with elliptical evergreen leaves. Indeed, the various species of Gnetum exhibit features that suggest a close link with flowering plants. This has led some to hypothesize that they represent a sort of living "link" between gymnosperms and angiosperms. We will get to that in a bit. First, we must taker a closer look at these odd plants.

Photo by Forest and Kim Starr licensed under CC BY 2.0

We will start with their leaves. They are quite strange by gymnosperm standards. Gnetum produce elliptical leaves with reticulate or web-like venation. Also, their vascular tissues contain vessel elements. Such traits are usually associated with dicotyledonous angiosperms. Characteristics such as these explain why the taxonomic position of Gnetaceae has floundered a bit over the years. What about reproduction? Surely that can help gain a better understanding of where this groups stands taxonomically.

Gnetum reproductive bits require a bit of scrutiny. They are certainly not what we would call flowers. They aren't quite cones either. The technical term for gymnosperm reproductive structures are stobili. In Gnetum, these arise from the axils of the leaves. They are strange looking structures to say the least. Male strobili are long and cylindrical. They, of course, produce pollen. They also contain infertile ovules whose function I will get to in a minute. Female strobili, on the other hand, are larger and consist of ovules enclosed in a thin tissue or integument.

Photo by Kware Ji licensed under CC BY 2.0

Pollination in Gnetum is largely accomplished via insects, though wind plays a significant role for some species as well. In insect pollinated species, the female strobili emit a strong odor and secret tiny beads of liquid called "pollination droplets." Pollination droplets are also secreted from the sterile ovules on the male strobili. It was observed that moths were the main visitors for at least two species of Gnetum.  The reason both sexes produce pollination droplets is to ensure that moths will visit multiple individuals in their search for food.

Following pollen transfer, even more angiosperm-like activity takes place. Some Gentum undergo a type of double fertilization that is unique among moat gymnosperm lineages. Double fertilization is largely considered a defining feature of flowering plants. It is a process by which two sperm cells unite with an egg and become the embryo and the nutritive endosperm that will fuel seedling growth. Along with its cousin Ephedra, Gnetum double fertilization also involves two sperm cells, though the end result is a bit different. Instead of forming an embryo and an endosperm, double fertilization in Gentum (and Ephedra) results in the formation of two viable zygotes and no endosperm.

Photo by Forest and Kim Starr licensed under CC BY 2.0

Fertilized seeds gradually swell into large drupe-like structures. Integument tissues develop with the seed, covering it in a fruit-like substance that turns from green to red as it matures. As far as anyone knows, birds are the main seed dispersal agents for most Gnetum species. 

Taken together, their peculiar anatomy and intriguing pollination have led many to suggest that Gnetum are more closely allied to flowering plants than they are gymnosperms. Certainly it is easy to draw lines from one dot to another in this case but the real test lies in DNA. Are they highly derived gymnosperms or possibly a so-called missing link? 

No. Recent work by the Angiosperm Phylogeny Group found that Gnetaceae are more closely related to the family Pinaceae than they are any of the sister angiosperm lineages. Their work also revealed that, although this lineage arose some 250 million years ago, much of the diversity we see today is the result of rapid speciation events during the Oligocene and Miocene. It would appear that these derived gymnosperms are not the missing link they we once thought to be. In fact, the whole concept of an evolutionary missing link is flawed to begin with. 

Photo by Ahmad Fuad Morad licensed under CC BY-NC-SA 2.0

Still, this should not take away from fully appreciating the bizarre nature of this family. The uniqueness of the genus Gnetum is certainly worth celebrating. They serve as a reminder of just how diverse gymnosperms once were. Today they are a mere shadow of their former glory, overshadowed by the bewildering diversity of angiosperms. If you encounter a Gnetum, take the time to appreciate it as a representative of just how strange gymnosperms can be. 

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

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

Can Plants "Hear" Running Water?

Photo by Jun Seita licensed under CC BY 2.0

A recently published study suggests that some plants are capable of using sound to locate water. That's right, sound. Although claims of plants liking or disliking certain types of music still belong in the realm of pseudoscience, this research does suggest that plants may be capable of detecting vibrations in an interpretable way. 

To test this idea, Dr. Monica Gagliano of the University of Western Australia germinated pea seeds in specially designed mazes. Each maze looked like an upside-down Y. At the end of each arm, she devised a series of treatments that would force the pea seedlings to "choose" their desired rooting direction. In some treatments she used standing water coupled with water running through a tube. In others she simply played the sounds of running water against the sound of white noise.

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The peas were allowed to grow for five days and afterwards were checked to see which direction their roots were growing. Amazingly, the peas seemed to be able to distinguish the sound of actual running water even when there was no moisture gradient present. Peas given the option of sitting or running water in a tube grew their roots towards the tube a majority of the time. Again, this was in the absence of any sort of water gradient in order to eliminate the chances that the peas were simply honing in on humidity.

Interestingly, plants that were played the sound of running water and white noise through speakers seemed to do what they could to avoid the noise. Although the research did not investigate why the peas had an aversion to the recordings, Dr. Gagliano suspects that it might have something to do with the low frequency magnetic currents emitted by the speakers. Previous research has shown that even weak localized magnetic fields are enough to disrupt the structure of developing root cells. 

All of this taken together paints a fascinating picture of plant sensory capabilities. One should take note, however, that the sample sizes used in this experiment were quite small. More, larger experiments will be needed to fully understand these patterns as well as the mechanisms behind them. Still, these findings shed light on cases in which tree roots seem to be so adept at finding sewer pipes, even in the absence of leaks. It also lends to the findings that the roots of trees such as scrub oaks and box elders will often opt for more stable and reliable sources of ground water over the fluctuating uncertainty of nearby stream sources. Finally, there is something to be said that we share as many as 10 of the 50 genes involved in human hearing with plants.

Our understanding of plant sensory capabilities is really starting to blossom (pun intended). Plants aren't the static, sessile organisms so many make them out to be. They are living, breathing organisms fighting for survival. I, for one, am excited for what new discoveries await. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

I've Got the Colorado Blues

Dave Powell, USDA Forest Service (retired), Bugwood.org licensed under a Creative Commons Attribution 3.0 License.

You would be hard pressed to find a resident of temperate North America who has never seen a Colorado blue spruce. These iconic trees are a staple of every sapling give-away and can be found in countless landscape plans all over the continent. There is no denying the fact that the blue hues of Picea pungens have managed to tap into the human psyche and in doing so has managed to spread far beyond its relatively limited range. However, despite its popularity, few people ever really get to know this species. Even fewer will ever encounter it in the wild. Today I would like to introduce you to a brief natural history of Picea pungens. 

Despite its common name, P. pungens is not solely a denizen of Colorado. It can be found in narrow swaths of the Rocky Mountains of Wyoming, Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, and of course, central Colorado. There are also some rumored populations in Montana as well. It has a very narrow range compared to its more common relative, the Engelmann spruce (Picea engelmannii). Whereas some authors consider the Colorado blue spruce to be a subspecies of the Engelmann spruce, the paucity of natural hybrids where these two species overlap suggests otherwise. It is likely that Colorado blue spruce split off from this lineage at some point in the past and has been following its own evolutionary trajectory ever since.

Female cones are quite attractive when they emerge. Photo by JJ Harrison (https://www.jjharrison.com.au) licensed under CC BY-SA 3.0

One of the reasons P. pungens has become such a popular landscape tree is due to its extreme hardiness. Indeed, this is one sturdy tree species. Not only can it handle drought, P. pungens is also capable of surviving temperatures as low as -40 degrees Celsius with minimal foliar damage. Little stands in the way of a well established Colorado blue. In the wild it can be found growing on gentle mountain slopes at elevations of 6,000 to 10,000 feet (1,800 to 3000 m). It is also a long lived and highly fecund tree. The most highly productive seed years for P. pungens begin at age 50 and last until it reaches roughly 150 years of age. Seeds germinate best on bare soils, which probably keeps this species limited to these mountainous areas in the wild.

The typical female cone of the Colorado blue spruce. Photo by U.S. Fish and Wildlife Service Public Domain

Another component of its landscape popularity is its characteristic blue color. In reality, not all trees exhibit this coloration. Its blue hue is the result of epicuticular wax deposits on the leaves as they are produced in the spring. Individual trees rpduce varying amounts and consistencies of wax and therefore may not appear blue. Wax production seems to be controlled by a genetic factor and therefore is often a shared trait among isolated populations. The wax functions as sun screen, reflecting harmful UV rays away from sensitive developing foliage. This is why it is most prominent in new growth. The wax can and often does degrade over the span of a growing season, resulting in duller trees come fall. 

Despite how interesting this spruce is, Picea pungens, in my opinion, represents the epitome of lazy landscaping. Like Norway spruce (Picea abies) and Norway maples (Acer platanoides), P. pungens seems to be an all-too-easy choice for those looking to save a quick buck. As a result, countless numbers of these trees line streets and demarcate property boundaries. Though P. pungens is native to North America, its narrow home range makes its ecological function elsewhere quite minimal. Sure, one could certainly do worse than planting this conifer, but it nonetheless overshadows more ecologically friendly tree choices. If you are looking to add a new tree to your landscape, take a few minutes to search for more ecologically friendly species that are native to your region.

Photo Credit: [1] [2] [3]

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