The Creeping Strawberry Pine

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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 typical growth habit of the creeping strawberry pine.

The typical growth habit of the creeping strawberry pine.

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 picture 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.

This distinctive, small, trisaccate pollen grain is typical of what you find with Microcachrys whereas all other podocarps produce bisaccate pollen.

The creeping strawberry pine is what we call a peloendemic, 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.

Mature female cones look more like angiosperm fruit than a conifer cone.

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

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

Fossilized Flower Places Angiosperms in the Jurassic

1, style branches; 2, dendroid style; 3, sepal; 4, ovarian roof; 5, scale; 6, seed; 7, cup-form receptacle/ovary; 8, bract; 9, petal; 10, unknown organ (staminode?).  [SOURCE]

1, style branches; 2, dendroid style; 3, sepal; 4, ovarian roof; 5, scale; 6, seed; 7, cup-form receptacle/ovary; 8, bract; 9, petal; 10, unknown organ (staminode?). [SOURCE]

Despite their dominance on the landscape today, the origin of flowering plants is shrouded in mystery. The odds of any living material becoming fossilized is extremely rare and when you consider the delicate and ephemeral nature of most flowers, one can begin to understand why their fossils are so special. The last few decades have seen tantalizing evidence emerge from fossil beds dating to the Cretaceous Period but a recent set of fossils from China predate the oldest confirmed angiosperm fossils by 50 million years. That’s right, it would appear that flowering plants were already on the scene by the early Jurassic!

The fossils in question have been coined Nanjinganthus dendrostyla. They were discovered in China in a formation that dates back roughly 174 million years. To most of us they look like a bunch of dark, albeit elaborate smudges on the rocks. To a trained eye, however, these smudges reveal intricate anatomical details. Amazingly, the team of paleobotanists responsible for this discovery had a lot of material to work with. Descriptions were made on a whopping 264 specimens representing 198 individual flowers. This amount of data means that the declaration of angiosperm affinity stands on pretty solid ground.

A single  Nanjinganthus  flower  [SOURCE]

A single Nanjinganthus flower [SOURCE]

Aside from their age, there is a lot about these fossils that surprised researchers. Probably the biggest surprise is their overall appearance. Paleobotanists have long hypothesized that early angiosperm flowers likely resembled something akin to a modern day Magnolia and invoke floral features such as apocarpy, a superior ovary, and a lack of an obvious style as likely features to look for in ancient plant fossils. Surprisingly, Nanjinganthus does not seem to conform to many of these expectations.

One of the most striking features of these fossils are the styles. They are large and branched like tiny trees (hence the specific epithet “dendrostyla”). The tree-like appearance of the style suggests that early angiosperms likely did not rely on insects for pollination. The branches themselves greatly increase the amount of surface area available for pollen capture, which could mean that Nanjinganthus was wind pollinated.

Flowers of  Nanjinganthus  preserved in different states and their details. For specific details on each image, please see   SOURCE

Flowers of Nanjinganthus preserved in different states and their details. For specific details on each image, please see SOURCE

Another surprising feature is the presence of an inferior ovary that, by its very definition, sits below the sepals and petals. It has long been hypothesized that early angiosperms would exhibit superior ovaries so this discovery means that we must rethink our expectations of how flowers evolved. For instance, it suggests we may not be able to make broad inferences on the past based on what we see in extant angiosperm lineages. It could also suggest that the origin of flowering plants was not a single event but rather a series of individual occurrences. It could also be the case that the origin of flowering plants occurred much earlier than the Jurassic and that Nanjinganthus represents one of many derived forms. Only further study and more fossils can help us answer such questions.

Another way in which Nanjinganthus deviates from theoretical expectations is in the presence of both sepals and petals. Up until now, paleobotanists have been fond of the idea that petals arose much later in angiosperms, having evolved over time as leaves became more and more specialized for attracting pollinators. The fact that Nanjinganthus was likely wind pollinated yet had both sepals and petals is a bit of a conundrum and further emphasizes the need to revisit some of our long-held assumptions of flowering plant evolution.

Details of the sepal and petal as seen through different forms of microscopic analysis. For specific details on each image, please see  SOURCE .

Details of the sepal and petal as seen through different forms of microscopic analysis. For specific details on each image, please see SOURCE.

By far the most important feature present in these fossils are the ovaries. For any fossil to unequivocally qualify as an angiosperm, it must have seeds encased in an ovary. This, after all, is the main feature that separates angiosperms from gymnosperms. Indeed, Nanjinganthus does appear to fit this definition. Thanks to the sheer amount of fossils available for study, the team discovered that the seeds of Nanjinganthus were enclosed in a cup-like chamber that was sealed off from the outside world by a structure they refer to as an “ovarian roof.” This roof does not appear to have any sort of opening, which worked out quite nicely for paleobotanists as it prevented sediments from entering into the chamber, thus preserving the seeds or ovules (it is hard to tell where they were in the developmental process) for study. This feature more than all others secures its identity as a flowering plant.

Based on the sediments in which these flowers were fossilized, it appears that this plant grew close to water. Also, despite its abundance in this particular fossil layer, it very likely was not a common component of this Jurassic landscape. In reality we still have a lot to learn about Nanjinganthus. What we can say with some certainty at this point is that the presence of Nanjinganthus in the early Jurassic likely means that flowering plants arose even earlier. Nanjinganthus is most definitely not the first flower. We will probably never find the first of anything. It is an ancient flower though, predating all other discoveries by at least 50 million years. This is why paleontology is so incredible. Who knows what the next blow of a rock hammer will turn up!

 

EDIT (10/27/2018): Since writing this post it has come to my attention that there is quite a bit of controversy attached to the description of this fossil. Many have reached out informing me that these fossils may actually be a gymnosperm organ rather than a flower. Despite all of the outcry I have yet to see any published critiques on this particular controversy. I anxiously await more professional input on the subject but for now I have decided to keep the content of the original piece as is. Of course extraordinary claims require extraordinary evidence and not being a paleobotanist myself, I cannot trust hearsay on the internet as fact, no matter how vociferous, until I see it published in a peer reviewed outlet of some sort. Please stay tuned as this story develops! 

Photo Credits: [1]

Further Reading: [1]

The Rise and Fall of the Scale Trees

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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

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 the started branching, young trees would have resembled a bushy, green bottle brush.

Juvenile scale tree on the left & the adult on the right

Juvenile scale tree on the left & the adult on the right

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

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.

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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

The fossilized strobilus of a Lepidodendron

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”

A fossilized root or “stigmaria”

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] [3] [4] [5] [6] [7]

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

The Japanese Umbrella Pine

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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.”

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.”

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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.

A 49.5 million years old fossil of a Sciadopitys cladode.

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.

Cooksonia is one of the earliest land plants to have evolved.

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!

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

The real change came when plants began rooting themselves into the soil. 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 Early Days Of A Symbiosis?

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Despite the ubiquitous nature of symbioses across the globe, evidence of their origins is scant to say the least. Mostly we look for clues of their origin hidden within the fossil record. Excitingly, a series of fossils discovered in Scotland reveal what very well be the early days of plant-cyanobacterial interactions. Thanks to these exquisitely preserved fossils, we now have the earliest record of an association between these two groups of organisms.

The fossils themselves date back to the early Devonian, some 400 million years ago. They hail from a hot spring community which allowed wonderfully detailed preservation of everything down to the cellular level. Needless to say, this was a drastically different time for life on this planet. Plants were really starting to dominate the landscape. In the case of the fossil discoveries in question, one plant in particular is the star of this show. 

Meet Aglaophyton major. This odd looking plant would have been a common site in these sorts of habitats. It largely consisted of a small, leafless stem that branched as it ambled over the ground. These stems bore the stomata, which allowed gas exchange to occur. Every once in a while, a stem would throw up a reproductive structure called a sporangium, which housed the spores. At the ground level, the stems would occasionally produce root-like rhizoids that have been found in association with fossilized mycorrhizal fungi in the soil.

In total, A. major only stood about 18 cm in height. Though abundant, it was relatively small compared to some of the other vegetation coming online at this point in time. It is likely that A. major could tolerate occasional flooding. In fact, some have speculated that flooding may have been necessary for the germination of its spores. It's this periodic inundation with water that likely led to an interesting and tantalizing relationship with cyanobacteria. 

1. Transverse section through two typical axes showing the simple internal organization; slide P1828; bar = 1 mm. 2. Anatomy of the prostrate mycorrhizal axis (E = epidermis; OC = outer cortex; MAZ = mycorrhizal arbuscule-zone; IC = inner cortex; PIT = phloem-like tissue; CT = conducting tissue); slide P1612; bar = 150 μm. 3. Dense aggregate of cyanobacterial filaments in an area where the axis is injured and has exuded some type of wound secretion (opaque mass); slide P1289; bar = 100 μm. 4. Detail of Plate I, 3, showing part of the cyanobacterial aggregate; bar = 100 μm. 5. Intercellular cyanobacterial filaments near the mycorrhizal arbuscule-zone of the cortex (darker tissue in lower third of image); slide P3652; bar = 50 μm. 6. Group of filaments passing through the intercellular system of the outer cortex; slide P3652; bar = 20 μm.

1. Transverse section through two typical axes showing the simple internal organization; slide P1828; bar = 1 mm. 2. Anatomy of the prostrate mycorrhizal axis (E = epidermis; OC = outer cortex; MAZ = mycorrhizal arbuscule-zone; IC = inner cortex; PIT = phloem-like tissue; CT = conducting tissue); slide P1612; bar = 150 μm. 3. Dense aggregate of cyanobacterial filaments in an area where the axis is injured and has exuded some type of wound secretion (opaque mass); slide P1289; bar = 100 μm. 4. Detail of Plate I, 3, showing part of the cyanobacterial aggregate; bar = 100 μm. 5. Intercellular cyanobacterial filaments near the mycorrhizal arbuscule-zone of the cortex (darker tissue in lower third of image); slide P3652; bar = 50 μm. 6. Group of filaments passing through the intercellular system of the outer cortex; slide P3652; bar = 20 μm.

Cyanobacteria are probably best known for their contribution of oxygen to Earth's early atmosphere. What's more, many also fix nitrogen. That is why the fossil discovery of A. major with cyanobacteria in and around its cells is so exciting. These 400 million year old fossils provide the first evidence of a plant and cyanobacteria in an intimate association.

As mentioned above, the fossilization process was so thorough that it preserved subcellular structures. After thin sectioning some A. major stems, a team of researchers found filaments of cyanobacteria in the process of invading the plant and taking up residence. The cyanobacteria appears to be entering the plant through the stomatal openings along the stem. Once inside, the cyanobacteria show signs of colonazation of substomatal chambers as well as intercellular spaces within the plants tissues.

Although the authors cannot say whether this association was mutualistic or not, it nonetheless represents a model situation detailing how such a symbiotic relationship could have evolved in the first place. Because the cyanobacteria in question here is thought to be aquatic, the only way for it to move into the plant would have been during periodic flooding events. The idea that this could be simply an infection following the death of the plant was considered. However, the non-random distribution of cyanobacteria within A. major cells suggests that this relationship was no accident.

For now, the relationship between A. major and cyanobacteria was likely an "on-again–off-again incidental association" centered around flood events. The fact that A. major was already associated with mycorrhizal fungi at this point in Earth's history certainly suggests that the genetic adaptations necessary for symbiotic relationships were already in place. Though it isn't a smoking gun, these fossils provide the earliest evidence of plants' relationship with cyanobacteria.

Photo Credits: [1]

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

The First Trees Ripped Themselves Apart To Grow

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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.

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.

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

Although this seems quite detrimental, the overall structure of the tree would have been quite 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 pretty 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.

Photo Credits: [1] [2]

Further Reading: [1]

The Ginkophytes Welcome a New Member

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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.

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.

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.

 

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

Photo Credits: [1]

Further Reading: [1] [2]

A Fern 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 scientists usually only dream about. Clearly visible in the fossilized stem are subcellular structures like nuclei and even chromosomes in various stages of cell division!

 

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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 cinnamon fern (Osmundastrum cinnamomeum). Based on the fossil evidence, cinnamon ferns were not only around during the early Jurassic, they have remained virtually unchanged for 180 million years. Talk about a living fossil!

Further Reading: [1]

Tomatillos Just Got A Lot Older

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"

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

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

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

Fossilized Forest

A fossilized forest discovered in Arctic Norway is shedding light on one of the earliest forests to have evolved on this planet. Preserved in situ, these fossils reveal what life was like for these plants some 380 million years ago.

This was the Devonian Era, a time in which plants were starting to conquer the land. During this time period, the land mass that is now Norway was located on the equator. The tropical climate of this time likely fostered the growth of these early forests, causing a race for the sky. For their time, these forests were monstrous in proportion.

The fossils are comprised of a long extinct species of plant known scientifically as Protolepidodendropsis pulchra. These "trees" were not any sort of tree that we would readily recognize. To see their closest living relatives today, you will have to take a knee. These were forebearers of the club mosses (Lycopodiaceae).

These forests stood around 4 meters (13 feet) in height. Even more peculiar, they grew densely packed with only about 20 centimeters separating each trunk. The trunks themselves were stunning having been covered in diamond-shaped plates. Like the club mosses, they reproduced by spores.

Another interesting thing about such discoveries is that it allows us to infer quite a bit about what was going on in the atmosphere as well. With such densely packed forests spreading over the land, the Devonian world was, for the first time, seeing a massive drawdown of atmospheric CO2 levels. Plants were changing the globe as they rose to prominence. Along the way, they were irrevocably changing the course of life on Earth.

Photo Credits: Cardiff University, Illustration by Dr. Chris Berry from Cardiff University

Further Reading:
http://geology.geoscienceworld.org/content/43/12/1043.full

Germinating a Seed After 32,000 Years

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?

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.

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

The Evolution of a Helicopter

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The whirring helicopter seeds of modern day conifers (as well as a handful of other tree species) are truly marvels of evolution. We humans have yet to top the simple efficiency of this form of locomotion. It is easy to see how such seed anatomy benefits a tree. Instead of plummeting to the ground and struggling under the shade of its parents, winged seeds are often carried great distances by the breeze. Such a dispersal mechanism is so effective that multiple tree lineages have converged on a single asymmetrical wing design of their samaras.  

The key to this type of seed dispersal lies in the movement of the seed in the air. The whirring motion allows the seeds to stay airborne as they are carried away from their cones. It would be all too easy to argue that any intermediate must be doomed to failure. However, this is not the case. A rich collection of 270 million year old fossils discovered in Texas is shining light on how at least one lineage of conifers settled in on this wonderful adaptation for seed dispersal. 

Artists reconstruction of a seed-bearing shoot of  Manifera talaris . Drawing by Ivo Duijnstee

Artists reconstruction of a seed-bearing shoot of Manifera talaris. Drawing by Ivo Duijnstee

Instead of producing one type of winged seed, an ancient species of conifer known scientifically as Manifera talaris produced multiple different samara designs. Some were symmetrical, others were double winged, and still others matched what we would readily recognize as a samara today. It would seem that early conifers were “trying out” many different forms of wind dispersed seed designs. Manifera talaris was alive during the early Permian. At that time, there were not many animals alive (that we are aware of) that could function as seed dispersers for conifers. Instead, these early trees relied on the wind to do the work for them. 

Though these fossils offer a unique window into the evolution of winged seeds, they do not give any indication as to how each seed designs would have performed. For paleobotanist Dr. Cindy Looy, this meant a chance to have a little fun with science. She and her colleagues built functional paper models of each of the samara types represented in the fossils. By attaching the paper wings to comparably sized seeds from an extant conifer, she was able to test the flight performance of each of these samara types. What she found was quite interesting. 

As it turns out, symmetric and asymmetric double-winged seeds performed quite poorly. They fluttered to the ground, barely achieving any rotation. Contrast this with the asymmetric single-winged seeds, which stayed airborne for twice as long as any other samara design. What this research shows is that early conifers were, in a sense, "experimenting" with different samara designs. Those designs that allowed for greater seed dispersal produced more trees that did the same. 

Photo Credit: Dr. Cindy Looy

Further Reading: [1]


Ancient Equisetum

Whenever you cross paths with an Equisetum, you are looking at a member of the sole surviving genus of a once great lineage. The horsetails, as they are commonly called, hit their peak during the Devonian Era, some 350 + million years ago. Back then, they comprised a considerable portion of those early forests. Much of the world's coal deposits are derived from these plants.

The horsetails once towered over the landscape, reaching heights of 30 meters or more. Today, however, they have been reduced to mostly small, lanky plants. The tallest of the extant horestails are the giant horsetail (Equisetum giganteum) and the Mexican giant horsetail (Equisetum myriochaetum) of Central and South America. These two species are known to reach heights of 16 ft. (4 m.) and 24 ft. (7 m.) respectively. Certainly an impressive site to see.

Equisetum giganteum (Chad Husby for scale.)

Equisetum giganteum (Chad Husby for scale.)

As a genus, Equisetum is composed of somewhere around 20 species, with many instances of hybridization known to occur. Most species tend to frequent wet areas, though dry, nutrient poor soils seem to suit some species just fine. The horsetails are known for their biomineralisation of silica, earning some the common name of "scouring rush." Settlers used to use these plants to clean their pots and pans. However, this is certainly not why this trait evolved. It is likely that the silicates have something to do with structural support as well as physical protection against pathogens. More work needs to be done looking at the benefits rather than the mechanisms involved.

Equisetum myriochaetum

Equisetum myriochaetum

Though they are not ferns, horsetails are frequently referred to as "fern allies." This is due to the fact that, like ferns, horsetails are not seed plants. Instead, they produce spores and exhibit a distinct alternation of generations between the small, gamete-producing gametophyte and the tall spore-producing sporophyte. Spores are produced from a cone-like structure at the top of the stem called a stobilus. This may be attached to the photosynthetic stem or it can arise as its own non-photosynthetic stem. Either way it is an interesting structure to encounter and well worth studying under some form of magnification.

Despite their diminutive appearance, many horsetails are quite hardy and thrive in human disturbance. For this reason, horsetails such as E. hyemale and E. arvense have come to be considered aggressive invasive species in many areas. They thrive in nutrient poor soils and their deep, wide-ranging rhizomes can make control difficult to impossible. There is something to be said for these little plants. Love them or hate them, they have stood the test of time. They were some of the first plants on land and it is likely that some will be here to stay, even if we go the way of the Devonian forests.

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

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