In Defense of Plants Book Coming February 2021!

I am extremely excited to announce that I have written a book! In Defense of Plants: An Exploration Into the Wonder of Plants is slated for release on February 16th, 2021 wherever books are sold.

“In Defense of Plants changes your relationship with the world from the comfort of your windowsill.

The ruthless, horny, and wonderful nature of plants. Understand how plants evolve and live on Earth with a never-before-seen look into their daily drama. Inside, Candeias explores the incredible ways plants live, fight, have sex, and conquer new territory. Whether a blossoming botanist or a professional plant scientist, In Defense of Plants is for anyone who sees plants as more than just static backdrops to more charismatic life forms.

In this easily accessible introduction to the incredible world of plants, you'll find:

• Fantastic botanical histories and plant symbolism

• Passionate stories of flora diversity and scientific names of plant organisms

• Personal tales of discovery through the study of plants

If you enjoyed books like The Botany of Desire, What a Plant Knows, or The Soul of an Octopus, then you'll love In Defense of Plants.”

You can pre-order In Defense of Plants here:

Amazon- https://amzn.to/3mBA1Ov

Bookshop- https://bit.ly/3lxih5B

Barnes and Noble- https://bit.ly/3qpE570

How Trees Are Shaping Treehoppers

Photo by Judy Gallagher licensed under CC BY-ND 2.0.

The sessile nature of plants means that they are strongly shaped by their environment. Natural selection is constantly at work on plants but that doesn’t mean that plants don’t shape their environment as well. When I think about the impact of plants on resident animal communities, I am always reminded of a quote by artist Terence McKenna, “Animals are something invented by plants to move seeds around.” Now, I realize that the animal kingdom got its start long before plants came onto the scene but there are many threads of truth to this quote.

Take, for instance, the case of the two-marked treehopper (Enchenopa binotata). This wonderful little insect enjoys a distribution that encompasses much of North and Central America, ranging from Canada down into Panama. Not only do these treehoppers look cool with their intriguing color pattern and that thorny pronatum, but their ecology and evolutionary history is absolutely fascinating as well. The existence of these treehoppes is entirely tied to the trees on which they live and breed. Moreover, while the two-marked treehopper may look like a single species, it is actually a complex of multiple cryptic “species” whose entire identity is owed to their preferred host tree.

Photo by Katja Schulz licensed under CC BY-ND 2.0.

The two-marked treehopper is not a species that moves around the landscape very much. While males will venture out into the environment in search of mates, females tend to live out their whole lives feeding and breeding on the tree upon which they were born. After mating, a female will lay her eggs within the stem of the host tree. The eggs overwinter in a sticky secretion called “egg froth.” This egg froth not only protects the eggs, it is also full of pheromones that signal to other females in the area to lay their eggs near by. The nymphs of the two-marked treehopper are gregarious. There is safety in numbers and the more nymphs hanging out on a branch, the less likely any single individual will be attacked by a predator.

Come spring, as trees begin to break dormancy, eggs laid the previous summer get the cue to hatch as sap begins to flow. Since treehoppers are sap feeders, this signal is essentially a ringing dinner bell. Apparently the specificity of this sap feeding habit is one of the reasons these treehoppers are so specific about their host.

As I mentioned earlier, the two-marked treehopper is not a single species but rather a complex of distinct taxonomic units. All of this cryptic diversity has to do with their preferred trees as each species within the complex feeds and breeds on a specific genus of tree/shrub: Carya, Celastrus, Cercis, Juglans, Liriodendron, Ptelea, Robinia, and Viburnum. Because no two tree species are alike, each has its own phenology. Different trees leaf out and begin growth at different times. Different tree species have different chemicals and nutrients in their sap. Also, different tree species have different wood densities. All of these factors and more have left their mark on the evolution of two-marked treehoppers.

Because females generally don’t leave the trees on which they were born, their offspring will inevitably be born on the same species of tree. This means they will be raised on a diet of the same sap as their mother. As mentioned, different trees produce different kinds of sap, which means that the digestive systems of these insects become highly tuned to their specific host tree. By experimentally moving two-marked treehopper nymphs to different host trees and tracking their development, scientists have also been able to demonstrate that host switching does not work well for the treehoppers. Nymphs raised on species different than the tree on which their eggs were laid do not develop as well or at all. It appears that their specific feeding habits are entirely tuned to the chemical composition of their host sap.

Additionally, the phenology of their host tree life cycle means that species raised on different trees rarely sync up in nature. Some trees force their resident treehoppers to emerge and mate earlier than others and vice versa. Evidence for this was made even stronger by studying these dynamics in the human environment.

The preferred hosts of two-marked treehoppers rarely grow in the same habitats in nature. However, thanks to our gardening and landscaping efforts, it isn’t hard to find these species in close proximity in the human environment. In cases where different host trees are found only a few meters from one another, the specific feeding requirements of each species means that species barriers among different treehopper populations are maintained. However, even before offspring enter into the picture, host trees also seem to have an effect on two-marked treehopper mating habits.

Waveforms of male signals for nine species in the Enchenopa binotata complex based on host tree identity [SOURCE].

Treehoppers are surprisingly musical creatures. Though we can’t hear them without the help of microphones, treehoppers utilize different types of vibrational calls to communicate with one another. This is especially true during mating. Males make repeated vibrations on the stems that the females will then respond to. By studying variations in these calls, scientists have found that two-marked treehoppers living on different trees produce vastly different calls. They key to this appears to lie in the ability of vibrations to travel through wood. Just as different types of wood work well for different types of instruments, the differences in wood density of their host trees affect how their mating calls travel and are eventually perceived. In other words, with a bit of training and some good recordings, you could identify the tree on which a two-marked treehopper lives just by its calls.

The ecological barriers between these insects are maintained no matter how close they are to one another and it is all thanks to the biology of the trees on which they live. Keep an eye out for these wonderful little insects. They are a joy to watch and offer us plenty of examples of evolution in action.

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

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

The Tecate Cypress: A Tree Left Hanging in the Balance

Photo by Anthonysthwd licensed under CC BY-SA 4.0

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

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

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

Photo by Stan Shebs licensed under CC BY-SA 3.0

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

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

Photo by Stan Shebs licensed under CC BY-SA 3.0

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

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

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

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

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

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

On the Ecology of Krameria

Photo by Stan Shebs licensed under CC BY-SA 3.0

There is something satisfying about saying "Krameria." Whereas so many scientific names act as tongue twisters, Krameria rolls of the tongue with a satisfying confidence. What's more, the 18 or so species within this genus are fascinating plants whose lifestyles are as exciting as their overall appearance. Today I would like to give you an overview of these unique parasitic plants.

Commonly known as rhatany, these plants belong to the family Krameriaceae. This is a monotypic clade, containing only the genus Krameria. Historically there has been a bit of confusion as to where these plants fit on the tree of life. Throughout the years, Krameria has been placed in families like Fabaceae and Polygalaceae, however, more recent genetic work suggests it to be unique enough to warrant a family status of its own. 

Regardless of its taxonomic affiliation, Krameria is a wonderfully specialized genus of plants with plenty of offer the biologically curious among us. All 18 species are shrubby, though at least a couple species can sometimes barely qualify as such. They are a Western Hemisphere taxon with species growing native as far south as Paraguay and Chile and as far north as Kansas and Colorado. They generally inhabit dry habitats.

Photo by Stan Shebs licensed under CC BY-SA 3.0

As I briefly mentioned above, most if not all of the 18 species are parasitic in nature. They are what we call "hemiparasites" in that despite stealing from their hosts, they are nonetheless fully capable of photosynthesis. It is interesting to note that no one (from what I have been able to find) has yet been able to raise these plants in captivity without a host. It would seem that despite being able to photosynthesize, these plants are rather specialized parasites. 

That is not to say that they have evolved to live off of a specific host. Far from it actually. A wide array of potential hosts, ranging from annuals to perennials, have been identified. What I find most remarkable about their parasitic lifestyle is the undeniable advantage it gives these shrubs in hot, dry environments. Research has found that despite getting a slow start on growing in spring, the various Krameria species are capable of performing photosynthesis during extremely stressful periods and for a much longer duration than the surrounding vegetation. 

Photo by mlhradio licensed under CC BY-NC 2.0

The reason for this has everything to do with their parasitic lifestyle. Instead of producing a long taproot to reach water reserves deep in the soil, these shrubs invest in a dense layer of lateral roots that spread out in the uppermost layers of soil seeking unsuspecting hosts. When these roots find a plant worth parasitizing, they grow around its roots and begin taking up water and nutrients from them. By doing this, Krameria are not limited by what water or other resources their roots can find in the soil. Instead, they have managed to tap into large reserves that would otherwise be locked away inside the tissues of their neighbors. As such, the Krameria do not have to worry about water stress in the same way that non-parasitic plants do. 

Photo by Stan Shebs licensed under CC BY-SA 3.0

By far the most stunning feature of the genus Krameria are the flowers. Looking at them it is no wonder why they have been associated with legumes and milkworts. They are beautiful and complex structures with a rather specific pollination syndrome. Krameria flowers produce no nectar to speak of. Instead, they have evolved alongside a group of oil-collecting bees in the genus Centris.

One distinguishing feature of Krameria flowers are a pair of waxy glands situated on each side of the ovary. These glands produce oils that female Centris bees require for reproduction. Though Centris bees are not specialized on Krameria flowers, they nonetheless visit them in high numbers. Females alight on the lip and begin scraping off oils from the glands. As they do this, they inevitably come into contact with the stamens and pistil. The female bees don't feed on these oils. Instead, they combine it with pollen and nectar from other plant species into nutrient-rich food packets that they feed to their developing larvae.  

Photo by João Medeiros licensed under CC BY 2.0

Following fertilization, seeds mature inside of spiny capsules. These capsules vary quite a bit in form and are quite useful in species identification. Each spine is usually tipped in backward-facing barbs, making them excellent hitchhikers on the fur and feathers of any animal that comes into contact with them.  

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

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

The Ginkophytes Welcome a New Member

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

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

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

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

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

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

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

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

Photo Credits: [1]

Further Reading: [1] [2]

Meet the Redbuds

I look forward to the blooming of the redbuds (Cercis spp.) every spring. They paint entire swaths of forest and roadside with a gentle pink haze. It’s this beauty that has led to their popularity as an ornamental tree in many temperate landscapes. Aside from their appeal as a specimen tree, their evolutionary history and ecology is quite fascinating. What follows is a brief introduction to this wonderful genus.

The redbuds belong to the genus Cercis, which resides in the legume family (Fabaceae). In total, there are about 10 species disjunctly distributed between eastern and western North America, southern Europe, and eastern Asia. The present day distribution of this genus is the result of vicariance or the geographic separation of a once continuous distribution. At one point in Earth’s history, the genus Cercis ranged from Eurasia to North America thanks to land bridges that once connected these continents. At some point during the Miocene, this continuous distribution began to break apart. As the climate changed, various Cercis began to diverge from one another, resulting in the range of species we know and love today.

All of them are relatively small trees with beautiful pink flowers. Interestingly enough, unlike the vast majority of leguminous species, redbuds are not known to form root nodules and therefore do not form symbiotic relationships with nitrogen-fixing bacteria called rhizobia. This might have something to do with their preference for rich, forest soils. With plenty of nitrogen available, why waste energy growing nodules? Until more work is done on the subject, its hard to say for sure why they don’t bother with nitrogen fixers.

One of the most interesting aspects of the redbuds are their flowers. We have already established that they are very beautiful but their development makes them even more interesting. You have probably noticed that they are not borne on the tips of branches as is the case in many flowering tree species. Instead, they arise directly from the trunks and branches. This is called "cauliflory," which literally translates to "stem-flower." In older specimens, the trunks and branches become riddled with bumps from years of flower and seed production.

It's difficult to make generalizations about this flowering strategy. What we do know is that it is most common in dense tropical forests. Some have suggests that producing flowers on trunks and stems makes them more available to small insects or other pollinators that are more common in forest understories. Others have suggested that it may have more to do with seed dispersal than pollination. Regardless of any potential fitness advantages cauliflory may incur, the appearance of a redbud covered in clusters of bright pink flowers is truly a sight to behold.

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

Cedar-Apple Rust

Photo by Rocky Houghtby licensed under CC BY 2.0

I have had my eye on these strange brown golf ball shaped growths growing on the twigs of a cedar in my neighborhood for about a year now. I first took notice of them late last spring. They looked pretty nasty but I knew they had to be something interesting. Indeed, “interesting” doesn't even come close to describing their true nature. 

These odd little growths are actually a single stage in the complex life cycle of a group of fungi in the genus Gymnosporangium. Collectively they are referred to as cedar-apple galls. Its a group of fungi whose hosts include junipers and relatives of the apple. Wherever these two lineages coexist you are bound to find this fungus. 

Gymnosporangium exhibit a fascinating life cycle that includes multiple hosts. The golf ball shaped galls will appear on the twigs of a juniper nearly a year after being infected with spores. They grow in size until they reach a point in which they will barely fit in the palm of your hand, though not all reach such proportions. The gall itself is covered in a series of uniform depressions, making it look a little out of place in a natural setting. After a year on a juniper tree, the galls enter into their next stage of development. 

Photo by klm185 licensed under CC BY 2.0

Usually triggered by the first warm rains of spring, strange gelatinous protrusions start to poke out of each depression on the gall's surface. These protrusions continue to swell until the entire gall is covered in bright orange, finger-like masses. These are where the spores are produced. The spores, however, cannot infect another juniper. Instead, they need to land on the next host to complete their life cycle. 

If the spores land on a member of the family Rosaceae (species within the genus Malus are preferred), then the second stage of the life cycle begins. Spores can germinate on both the leaves and the fruit but instead of turning into a large brown gall, they take on a different appearance. This is what makes this fungus readily apparent as a type of rust. A patch of orange will begin to grow. Upon closer inspection one can see that the orange patch is actually a series of small cup-like structures full of spores. 

Come fall, the spores are ready to be dispersed by wind. With any luck, they will land back on a juniper tree and the cycle will start anew. Because of its propensity for apple crops, cedar-apple rust fungi are considered to be a serious pest in apple orchards. In a more natural setting, however, it is a bizarrely unique fungus worth looking for.

Photo Credits: [1] [2]

Further Reading: [1] [2]

Rusty Mustards

Believe it or not, what you are seeing here is the same species of plant. The one on the left is the normal reproductive state of a Boechera (Arabis) mustard while the one on the right is the same species of mustard that has been infected by a rust fungus known as Puccinia monoica.

The interaction of these two species is interesting on so many levels. I spent an entire summer, along with my botanical colleagues, completely stumped as to what this strange orange-colored plant could be only to eventually find out that it was a mustard that has been hijacked! The fungus in question, P. monoica, is part of a large complex of interrelated rust fungi who are quite fond of mustards. The reason for this all boils down to reproduction.

The lifecycle of P. monoica begins when spores land on a young mustard plant and invade the host tissue. As they grow, they gain more and more nutrients from the mustard. Eventually the fungi effectively sterilizes the mustard and causes it to begin forming what are referred to as "pseudoflowers." The pseudoflowers are basically leaves that have been mutated by the fungus to look and smell a lot like other plants blooming in early summer.

The pseudoflowers produce a sticky, nectar-like substance that is very attractive to pollinators. The mimicry even goes as far as to produce yellowish pigments that reflect UV light, making them an even more irrisistable target for passing insects. On each pseudoflower are hundreds of small cups known as spermatogonia. These house the sex cells of the fungus. Visiting insects get covered in these sex cells, which they will then transfers to other infected plants thus achieving sexual reproduction for the fungus.

Still with me?

At this point, the pseudoflowers stop producing color and nectar and instead, the fused sex cells germinate into hyphae that begin to form specialized structures called "aecia." The aceia house the spores that will be responsible for infecting their secondary host plants, which are grasses. Spores blow about on the wind and, with a little luck, a few will land on a blade of grass. The spores germinate and infect the grass. From there, structures called "uredia" are formed that go on to produce even more spores to infect even more grass. Eventually, structures called "telia" are formed on the grass and the cycle finally comes full circle. The telia produce the spores that will go on to infect the original mustard host plants.

Whew! To have stumbled across an evolutionary drama such as this serves as a reminder of just how much in nature goes largely unnoticed every day.  

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