Goblin's Gold: the story of a luminous moss

Photo by Alpsdake licensed under CC BY-SA 4.0

Luminous moss, dragon’s gold, goblin’s gold… when a moss has this many common names, you know it must catch the eye. Indeed, Schistostega pennata might just be one of the most dazzling of mosses around, that is provided you know where and how to look for it.

Let’s begin with a brief introduction. Goblin’s gold is the only member of both its genus (Schistostega) and family (Schistostegaceae). Despite its unique taxonomic position, it is nonetheless a widespread species, growing naturally throughout many temperate regions of the Northern Hemisphere.

When fully grown, the gametophyte stage of goblin’s gold sort-of resembles a tiny, green, semi-translucent feather. Small spore capsules are borne on the spindly stalk of the sporophyte and the resulting spores are said to be quite sticky. Instead of relying on wind to disperse its propagules, golbin’s gold utilizes animals. The spores are sticky enough that they get glom onto any insects or other small animals that brush up against them.

The mature gametophyte of Schistostega pennata. Photo by HermannSchachner licensed under Public Domain

None of this, however, gives a hint as to how it earned all of those colorful names. To find that out, one must be ready to brave dark, damp spaces like caves. You see, though it can grow in more open habitats, you are most likely to encounter goblin’s gold in dark crevices or under overhangs. It has been said that goblin’s gold does not compete well with other plants in most habitats, but that doesn’t mean it doesn’t have a few tricks up its stems that give it an edge in other types of habitats.

For most plants, caves and other dark places are a no go. They simply can’t get enough light to survive. Such is not the case for goblin’s gold. Instead of trying to compete with more aggressive vegetation, goblin’s gold occupies deeply shaded habitats that few other plants can. It owes its shade-tolerant abilities to a stage of its development most of us rarely think about, let alone notice.

Photo by Jymm licensed under CC BY-SA 4.0

When a moss spore germinates, it doesn’t immediately look like what we would recognize as a moss. Instead, it grows into thread-like, multicellular fillaments called a “protonema.” You can think of this as the juvenile stage of the gametophyte. The protonema spreads outward as it grows, gradually producing hormones and other growth regulators that will control the development of the mature gametophyte. Because goblin’s gold grows in such dark habitats, it can’t afford to grow its gametophyte anywhere. To grow long enough to reproduce, it has to find spots where there is enough light to complete its lifecycle.

This is where the protonema comes in. In much the same why that fungal hyphae fan out into the soil in search of food to decompose, goblin’s gold protonema fan out over the damp substrate, searching for spots where enough light filters through to fuel growth. Luckily, the protonema can make do with much less light that the mature gametophyte, which also happens to be how this tiny moss earned so many interesting nicknames.

When grown in deep shade, the protonema of goblin’s gold develops a layer of lens-shaped cells on its surface. The opposite side of each cell narrows to a cone. When light, no matter how weak, strikes these lens cells, the curvature focuses the light down into the cell so that it is concentrated into the tip at the bottom. Being able to sense the direction of the light, the chloroplasts within each cell can actually move around so that they are always in a position that maximizes their exposure. Through this process, each cell is able to concentrate what little light is available so that they can photosynthesize in light so low that nearly all other plants will starve.

[SOURCE]

The light concentrating mechanism of the goblin’s gold protonema happens to have a wonderful and stunning side effect. As light enters the lens, small amounts of it are refracted around the cell. When that refracted light mixes with the green light that isn’t absorbed by the chloroplasts, it bounces back into the environment, giving the whole protonemal mat a green florescent glow when viewed in just the right way.

By being able to make use of what little light finds its way into these dark habitats, goblin’s gold can grow largely free of competition. Also, the protonema itself is capable of asexual reproduction so colonies can grow to epic proportions in dark areas, only producing mature gametophytes in a few spots. Interestingly, there appears to be some plasticity to this light-concentrating habit as well. When observing goblin’s gold protonema that develop under high light conditions, researchers have found that they do not develop lens shaped cells and therefore are not capable of reflecting light in the same way.

Humans have known about this moss for centuries, even if they didn’t understand the mechanisms that cause it, and that is why this wonderfully unique species has earned so many common names.

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

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

Desert Mosses That Live Under Rocks

Syntrichia caninervis growing in both soil surface and milky quartz. [SOURCE]

To be accused of living under a rock is generally not a good thing in today’s society. That is, unless you are a moss living in the Mojave Desert. By setting up residency under milky quartz, a few Mojave mosses are able to find much more favorable growing conditions than they would in the surrounding desert environment.

Microclimates are extremely important, especially in harsh environments like the Mojave. By providing conditions that are ever so slightly better than ambient conditions, microclimates can increase the amount of habitat available, which can lead to greater biodiversity overall. That is exactly what is going on beneath milky quartz in high elevation habitats of the Mojave Desert.

Tortula inermis (white arrow) and S. caninervis (black arrow) growing in a milky quartz. [SOURCE]

While dabbling in a bit of mineral appreciation, bryologists from the University and Jepson Herbaria at UC Berkeley discovered bright green moss growing under some chunks of quartz. Whereas moss growing on the surface of soil and rocks throughout the region were dark, dry, and dormant, the moss growing under quartz was green, lush, and growing. This observation launched a series of experiments to better understand how milky quartz may be providing more favorable microclimates for some desert mosses.

By measuring the conditions under chunks of milky quartz and comparing it to that of the surrounding landscape, researchers found that these minerals do indeed provide mosses with much more favorable conditions. Moreover, the benefits to living under milky quartz are numerous, offering many advantages to resident mosses.

For starters, milky quartz serves as a buffer against large swings in temperature. Deserts are known for being extremely hot but they can also be extremely cold. Sandy soils may heat up very quickly when the sun is out but, by the same logic, they also cool extremely quickly as soon as the sun sets. Rapid swings in temperature can be very harmful to plants so anything that can buffer such swings is generally a good thing. That is exactly what milky quartz does. As the sun rises in the sky, it takes milky quartz longer to heat up than the surrounding landscape, which means the environment directly underneath stays cooler for longer. Similarly, once warmed by the sun, milky quartz takes longer to cool down as the sun sets. As such, the environment directly underneath doesn’t cool down as quickly. By monitoring temperatures over the course of a year, it was found that temperature swings under the quartz were buffered by an average of 4°C (7°F) compared to that of the surrounding environment.

Tortula inermis was more likely to be found growing under quartz at high elevations. [SOURCE]

Though widespread in the Mojave, Syntrichia caninervis nonetheless grows better under quartz. Photo by John Game licensed under CC BY 2.0

Another benefit to living under quartz involves humidity. Not only are deserts hot, they can also be very dry. The Mojave is certainly no exception to this rule as it is considered the driest desert in North America. A lack of water can be troublesome for mosses. Because they lack roots and a vascular system, mosses rely on osmosis for obtaining the water they need to grow and reproduce. They also lose water and dehydrate quickly. For individuals growing exposed to the elements, this means drying up and going dormant. Mosses simply can’t grow when water isn’t around. By monitoring the relative humidity under milky quarts, researchers found that the undersides of milky quartz were twice as humid as the surrounding landscape.

Thanks to this increased humidity, mosses living under milky quartz are able to hold onto water for much longer than mosses growing on exposed soil. This has both short and long-term consequences for moss growing seasons in this harsh desert ecosystem. Increased humidity under milk quartz prolongs the moss growing season much longer than that of their exposed neighbors. In support of this, the researchers found that mosses growing under milky quartz also grew longer shoots. Longer shoots also means more water storing capabilities, which very well could lead to a positive feedback loop between humidity, growing season, and moss health.

(A) Box plot of hypolithic and soil surface S. caninervis shoot length. (B) An S. caninervis shoot fromunder quartz. (C) An S. caninervis shoot from the soil surface. [SOURCE]

Finally, milky quartz may actually protect resident mosses from the blistering rays of the sun. Growing at high elevation means much more exposure to the power of the sun. When fully exposed, desert mosses will often pump their tissues full of pigments like carotenoids, anthocyanins, and flavonoids, which act as sunscreens, protecting their sensitive tissues from UV damage. Even so, exposed mosses can suffer greatly from sun damage and, while dormant, have no means of repairing said damage.

By monitoring the light environment directly under milky quarts, researchers found that, depending on the size of the rock, light transmittance is reduced down to anywhere between 4% and 0.04% of full exposure. Moreover, the crystalline structure of milky quartz is such that it may actually filter out both UV-A and UV-B radiation, thus further reducing the harmful effects of the sun. In fact, mosses growing under milky quartz were found to produce far less sunscreen pigments than their exposed neighbors. If they don’t have to protect themselves from the blistering sun, it appears they don’t waste the energy on such pigments. While a reduction in light may sound bad for a photosynthetic organism, it would appear that the mosses in this study are well adapted to photosynthesizing at lower light levels.

In effect, milky quartz acts like parasols for desert mosses. Just as we like to sit under umbrellas at the beach, these desert mosses find much more favorable growing conditions under milky quartz. While none of the mosses in the study are restricted to growing under quartz, those that do experience multiple measurable benefits that increase their growing season in this largely unforgiving desert ecosystem.

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

Further Reading: [1]

The Peculiarly Tiny World of Buxbaumia Mosses

Photo by Tab Tannery licensed under CC BY-NC-SA 2.0

Bug moss, bug-on-a-stick, humpbacked elves, elf-cap moss… Who knew there could be so many names for such tiny mosses. Despite their small stature, the mosses in the genus Buxbaumia have achieved something of a celebrity status to those aware of their existence. To find them, however, you need a keen eye, lots of patience, and a bit of luck.

Buxbaumia aphylla. Photo by Bernd Haynold licensed under CC BY-SA 4.0

Buxbaumia comprises something like 12 different species of moss scattered around much of the Northern Hemisphere as well as some parts of Australia and New Zealand. They are ephemeral in nature, preferring to grow in disturbed habitats where competition is minimal. More than one source has reported that they are masters of the disappearing act. Small colonies can arise for a season or two and then disappear for years until another disturbance hits the reset button and recreates the conditions they like.

Buxbaumia viridis. Photo by BerndH licensed under CC BY-SA 3.0

I say you must have a keen eye and a lot of patience to find these mosses because, for much of their life, the exist on a nearly microscopic scale. Buxbaumia represents and incredible example of a reduction in body size for plants. Whereas the gametophytes of most mosses are relatively large, green, and leafy, Buxbaumia gametophytes barely exist at all. Instead, most of the “body” of these mosses consists of thread-like strands of cells called “protonema.” Though all mosses start out as protonema following spore germination, it appears that Buxbaumia prefer to remain in this juvenile stage until it comes time to reproduce.

Buxbaumia viridis. Photo by Bernd Haynold licensed under CC BY-SA 4.0

Considering how small the protonemata are, there has been more than a little confusion as to how Buxbaumia manage to make a living. Early hypotheses suggested that these mosses were saprotrophs, living off of nutrients obtained from chemically digesting organic material in the soils. However, it is far more likely that these mosses rely heavily on partnerships with mycorrhizal fungi and cyanobacteria for their nutritional needs. It is thought that what little photosynthesis they perform is done via their protonema mats and developing sporophyte capsules.

Buxbaumia viridis. Photo by Bernd Haynold licensed under CC BY-SA 3.0

Speaking of sporophytes, these are about the only way to find Buxbaumia in the wild. They are also the source of inspiration for all of those colorful common names. Compared to their gemetophyte stage, Buxbaumia sporophytes are giants. Fertilization occurs at some point in the fall and by late spring or early summer, the sporophytes are ready to release their spores. The size and shape of these capsules makes a lot more sense when you realize that they rely on raindrops for dispersal. When a drop impacts the flattened top of a Buxbaumia capsule, the spores are ejected into the environment and with any luck, will be carried off to another site suitable for growth.

Buxbaumia viridis. Photo by BerndH licensed under CC BY-SA 3.0

I encourage you to keep an eye out for these plants. It goes without saying that data on population size and distribution is often lacking for such cryptic plants. Above all else, imagine how rewarding it would be to finally cross paths with this tiny wonders of the botanical world. Happy botanizing!

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

An Introduction to Hornworts

Anthoceros sp. Photo by Bramadi Arya licensed under CC BY-SA 4.0

When was the last time you thought about hornworts? Have you ever thought about hornworts? If you answered no, you aren’t alone. Despite their global distribution, these tiny plants receive hardly any attention and that is a shame. Hornworts (Anthocerotophyta) have been around for a very long time. In fact, it is likely that they were some of the first plants to colonize the land roughly 300 - 400 million years ago.

To be fair, hornworts aren’t known for their size. They are generally small plants, though their colonies can form impressive mats. To find them, one must try looking in and among rocks, bare patches of soil, or pretty much anywhere enough moisture builds up to supply their needs. They tend to enjoy nutrient-poor substrates but I would hesitate to say that with any certainty. No matter where you live, from the tundra to the tropics, there is probably a hornwort native to your neck of the woods.

Dendroceros sp. Photo by J.Ziffer licensed under public domain

How many different species of hornwort there are is apparently the subject of some debate. Some authors recognize upwards of 300 species whereas others suggest the real number hangs somewhere around 150. Regardless of the exact numbers, hornworts belong to one of six genera: Anthoceros, Dendroceros, Folioceros, Megaceros, Notothylas and Phaeoceros. Fun fact, the suffix ‘ceros’ at the end of each genus is derived from the Latin word for ‘horn.’

The reason they are called hornworts is because of their reproductive structures or “sporophytes.” Similar to their moss and liverwort cousins, hornworts undergo an alternation of generations in order to reproduce sexually. The green gametophytes house the sexual organs - antheridia if they are male and archegonia if they are female. After fertilization, a sporophyte begins to grow, which will go on to produce and disseminate spores. However, the way in which the hornwort sporophyte forms is a bit different from what we see in mosses and liverworts.

Alternation of generations in hornworts. Photo by Mariana Ruiz (LadyofHats) licensed under public domain

Upon fertilization, the zygote begins to divide into a bulbous mass of cells affectionately referred to as "the foot.” This foot remains within the gametophyte throughout the lifetime of the hornwort, depending on the gametophyte for water and nutrients. Even more peculiar is the the fact that the growing point of the sporophyte is at the base rather than the tip. As such, the horn of each hornwort could continue to grow upwards until it is damaged in some way.

The horn itself is an amazing structure. Whereas the outside layers of tissue are merely structural, the internal tissues differentiate into two different types - spores and pseudo-elaters. Pseudo-elaters expand and contract as humidity fluctuates so as the sporophyte splits to release the spores, the pseudo-elaters dehydrate and snap like tiny spore catapults, thus aiding in their dispersal.

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

Of course, reproduction is the main goal but to get to that point, hornworts must grow and mature. How they manage to survive is incredible because it is a reminder that what are often thought of as “primitive” plants are actually far more advanced than we give them credit for. The main body of the hornwort gametophyte is a thin layer of cells that spread out to form a tiny, green mat. This is the structure you are most likely to encounter.

Inside each cell is a single chloroplast. In most hornworts, the chloroplast does not exist in isolation. Instead, it is fused with other organelles into a structure called a “pyrenoid.” The pyrenoid functions as both a center for photosynthesis and a food storage organ. This is unique as it relates to terrestrial plants but quite common in algae. Another odd fact about hornwort anatomy are the presence of tiny cavities scattered throughout their tissues. These cavities form as clusters of hornwort cells die. They then fill with a special mucilage that appears to invite colonization by nitrogen-fixing cyanobacteria. The cyanobacteria set up shop within the cavities and provides the hornwort with supplemental nitrogen in return for a place to live.

Anthoceros agrestis photo by BerndH licensed under CC BY-SA 3.0

Cyanobacteria aren’t the only organisms to have partnered with hornworts either. Mycorrhizal fungi also enter into the picture. A study done back in 2013 actually found that a wide variety of fungi will partner with hornworts which suggests that this symbiotic relationship is much more ancient and versatile than we once thought. Fungi cluster around parts of the gametophyte that produce root-like structures called “rhizoids,” offering nutrients in return for carbohydrates.

All in all, I think it is safe to say that hornworts are remarkable little plants. Though they can sometimes be difficult to find and properly identify, they nonetheless offer plenty of inspiration for the botanically inclined mind. We can all do better by tiny plants like the hornworts. They have been on land for an incredible amount of time and they definitely deserve our respect and admiration.

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

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

Glacier Mice

Photograph by Dr. Darrel Swift/Univeristy of Sheffield

At first glance the surface of a glacier hardly seems hospitable. Cold, barren, and windswept, glaciers appear to be the antithesis of life. However, this assumption is completely completely false. Glaciers are home to an interesting ecosystem of their own, albeit on a smaller scale than we normally give attention to.

From pockets of water on the surface to literal lakes of water sealed away inside, glaciers are home to a myriad microbial life. On some glaciers the life even gets a bit larger. Glaciers are littered with debris. As dust and gravel accumulate on the surface of the ice, they begin to warm ever so slightly more than the frozen water around them. Because of this, they are readily colonized by mosses such as those in the genus Racomitrium.

The biggest challenge to moss colonizers is the fact that glaciers are constantly moving, which anymore today means shrinking. As such, these bits of debris, along with the mosses growing on them, do not sit still as they would in say a forest setting. Instead they roll around. As the moss grows it spreads across the surface of the rock while the ice rotates it around. This causes the moss to grow on top of itself, inevitably forming a ball-like structure affectionately referred to as a "glacier mouse."

Because the moss stays ever so slightly warmer than its immediate surroundings, glacier mice soon find themselves teaming with life. Everything from worms to springtails and even a few water bears call glacier mice home. In a study recently published in Polar Biology, researcher Dr. Steve Coulson found "73 springtails, 200 tardigrades and 1,000 nematodes" thriving in just a single mouse!

The presence of such a diverse community living in these little moss balls brings up an important question - how do these animals find themselves in the glacier mice in the first place? After all, life just outside of the mouse is very brutal. As it turns out, the answer to this can be chalked up to how the mice form in the first place. As they blow and roll around the the surface of the glacier, they will often bump into one another and even collect in nooks and crannies together. It is believed that as this happens, the organisms living within migrate from mouse to mouse. The picture being painted here is that far from being a sterile environment, glaciers are proving to be yet another habitat where life prospers. Sadly, as climate change causes glaciers retreat at an ever increasing rate, glacier mice and all of the life they support will lose the very conditions they rely on for survival.

Photo Credit: [1] [2]

Further Reading: [1]

Meet The Powder Gun Moss

I get very excited when I am able to identify a new moss. This is mainly due to the fact that moss ID is one of my weakest points. I was sitting down on a rock the other day taking a break from vegetation surveys when I looked to my right and saw something peculiar. The area was pretty sloped and there was some exposed soil in the vicinity. Covering some of that soil was what looked like green fuzz. Embedded in that fuzz were these strange green urns.

I busted out my hand lens and got a closer look. This was definitely a moss but one I had never seen before. The urns turned out to be capsules. Later, a bit of searching revealed this to be a species of moss in the genus Diphyscium. This genus is the largest within the family Diphysciaceae and here in North America, we have two representatives - D. foliosum and D. mucronifolium.

These peculiar mosses have earned themselves the common name 'powder gun moss.' The reason for this lies in those strange sessile capsules. Unlike other mosses that send their capsules up on long, hair-like seta in order to disperse their spores on the faintest of breezes, the Diphyscium capsules remain close to the ground. In lieu of wind, a powder gun moss uses rain. In much the same way puffball mushrooms harness the pounding of raindrops, so too do the capsules of the powder gun moss. Each raindrop that hits a capsule releases a cloud of spores that are ejected into an already humid environment full of germination potential.

Luckily for moss lovers like myself, the two species of Diphyscium here in North America tend to enjoy very different habitats. This makes a positive ID much more likely. D. foliosum prefers to grow on bare soils whereas D. mucronifolium prefers humid rock surfaces. Because of this distinction, I am quite certain the species I encountered is D. foliosum. And what a pleasant encounter it was. Like I said, it isn't often I accurately ID a moss so this genus now holds a special place in my mind.

Further Reading: [1] [2]

The Tallest Moss

Photo by Doug Beckers licensed under CC BY-SA 2.0

For all the attributes we apply to the world of bryophytes, height is usually not one of them. That is, unless you are talking about the genus Dawsonia. Within this taxonomic grouping exists the tallest mosses in the world. Topping out around 60 cm (24 inches),  Dawsonia superba enjoys heights normally reserved for vascular plants. Although this may not seem like much to those who are more familiar with robust forbs and towering trees, height is not a trait that comes easy to mosses. To find out why, we must take a look at the interior workings of bryophytes. 

Mosses as a whole are considered non-vasular. In other words, they do not have the internal plumbing that can carry water to various tissues. Coupled with the lack of a cuticle, this means that mosses can be sensitive to water loss. For many mosses, this anatomical feature relegates them to humid environments and/or a small stature. This is not the situation for the genus Dawsonia. Thanks to a curious case of convergent evolution, this genus breaks the physiological glass ceiling and reaches for the sky. 

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Photo by Salsero35 licensed under CC BY-SA 4.0

Unlike other mosses, Dawsonia have a conduction system analogous to xylem and phloem. Being convergent, however, it isn't the same thing. Instead, the xylem-like tissue of these mosses is called the "hydrome" and is made up of cells called "hydroids." The phloem-like tissue is called the "leptome" and is made up of cells called "leptoids." These structures differ from xylem and phloem in that they are not lignified. Mosses never evolved the ability to produce this organic polymer. Regardless of their chemical makeup, Dawsonia vascular tissue allows water to move greater distances within the plant.

Another major adaption found in Dawsonia has to do with the structure of the leaves. Whereas the leaves of most mosses are only a few cells thick, the leaves of Dawsonia produce special cells on their surface called "lamella." These cells are analogous to the mesophyll cells in the leaves of vascular plants. They not only function to increase surface area and CO2 uptake, they also serve to maintain a humid layer of air within the leaf, further reducing water loss. 

All of this equates to a genus of moss that has reached considerable proportions. Sure, they are easily over-topped by most vascular plant species but that is missing the point. Through convergent evolution, mosses in the genus Dawsonia have independently evolved an anatomical strategy that has allowed them to do what no other extant groups of moss have done - grow tall.

Photo by Jon Sullivan licensed under CC BY-NC 2.0

Photo Credits: Wikimedia Commons, Doug Beckers, and Jon Sullivan

Further Reading: [1]