When Trillium Flowers Go Green

The first time I encountered a white trillium (Trillium grandiflorum) with green stripes on its flowers, I thought I had found a new variant. I excitedly took a bunch of pictures and, upon returning home, shared them among friends. It didn’t take long for someone far more informed than me to point out that this was not a new variant of this beloved plant. What I had found was signs of an infection.

The green stripes on the petals are the result of a very specific bacterial infection. The bacteria responsible belongs to a group of bacterial parasites collectively referred to as phytoplasmas. Phytoplasmas are not unique to trillium. In fact, these bacteria can be found around the world and infect many different kinds of plants from coconuts to sugarcane. Indeed, most of the research on phytoplasmas is motivated by their impacts on agriculture. Despite the damage they can cause, their natural history is absolutely fascinating.

Phytoplasmas are obligate parasites. They can only live long-term inside the phloem of their preferred host plants. Once inside the plant, phytoplasmas begin tinkering with cell expression, causing an array of different symptoms that (to the best of my knowledge) depend on their botanical host. In the case of trillium, phytoplasma infection causes a change in the flower petals. By altering gene expression, petal cells becoming increasingly leaf-like, resulting in the green striping I had observed. That isn’t all the phytoplasma does either. Infections usually result in complete sterilization of the flower. I have even heard some reports that the infected plants are also weakened to the point that they eventually die.

Why the phytoplasma do this has to do with their bizarre life cycle. Now, to be fair, much of what I have been able to gather on the subject comes from research done on other plant species. Still, there are enough commonalities among phytoplasma infections that I strongly suspect they apply to the trillium system as well. Nevertheless, take what I am saying here with a grain of salt.

As mentioned, phytoplasma can only exist long-term within the phloem of their plant host. They don’t produce any sort of fruiting bodies, nor are they transferred by air or contact with tissues. This creates a bit of an issue when it comes to finding new hosts, especially if infection inevitably results in the death of the plant. This is the point in which a vector must enter the picture.

The vector in question in many cases are sap-feeding insects like leafhoppers. Leafhoppers use their needle-like proboscis to pierce the phloem and suck out sap. It’s this feed behavior that phytoplasma capitalize on to complete their lifecycle. Moreover, the phytoplasma don’t do so passively. Just as the phytoplasma alter the gene expression in the petal cells, they can also alter the expression of genes involved in plant defenses.

Research on infected Arabidopsis plants has shown that phytoplasma cause the plant to decrease production of a hormone called jasmonate. This is fascinating because jasmonate is involved in defending plants against herbivory. It was found that when plants produced less jesmonate, leafhoppers were 30%-60% more likely to lay eggs on those plants. Essentially, the phytoplasma are reducing the plants’ defenses in such a way that there is a greater chance that they will be fed on by a greater number of sap-suckers.

As leafhoppers feed on the sap of infected plants, they inevitably suck up plenty of phytoplasma in the process. Through a complex series of events, the ingested phytoplasma eventually make their way into the salivary glands of the leafhopper. Then, as the leafhopper moves from plant to plant, piercing the phloem to feed, it inevitably transfers some of the phytoplasma in its saliva into a new host, thus completing the lifecycle of these plant parasites.

To bring it back to those green stripes on the trillium flowers, I suspect that by altering the petal cells to look more like leaves, the phytoplasma may be “encouraging” leafhoppers to concentrate their feeding on infected tissues. However, this is purely speculation on my part. The lack of data outside the agricultural realm represents an important scientific void that needs filling.

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

Early Spring Botanizing

SURPRISE!

Many have commented that a video component was lacking from the hiking podcasts. I have teamed up with filmmaker/producer Grant Czadzeck (www.grantczadzeck.com) to bring you a visual botanizing experience. I'm not sure how regular this will become but let us know what you think. In the mean time, please enjoy this early spring hike in central Illinois.

Trillium Morph

Did you know that there is a naturally occurring white morph of Trillium erectum? I was lucky enough this weekend to find this white one growing right next to its red counterpart. An exciting find indeed!

Trillium

Trillium. The very name is synonymous with spring wherever they grow. Even the non-botanically minded amongst us could probably pick one out of a lineup. This wonderful genus holds such a special place in my heart and I anxiously await their return every year. The journey from seed to flowering plant is an arduous one for a trillium and some may take for granted just how much time has elapsed from the moment the first root pushed through the seed coat to the glorious flowers we admire each spring. The story of a Trillium, like any other plant, starts with a seed.

As with many other spring ephemerals, Trilliums belong to that group of plants that utilize ants as seed dispersers. Once underground in an ant midden, a Trillium seed plays the waiting game. Known as double dormancy, their seeds germinate in two phases. After a year underground, a root will appear followed by an immature rhizome and cotyledon. Here the plant remains, living off of the massive store of sunlight saved up in the endosperm for yet another year. Following this second year underground, the plant will throw up its first leaf.

In its fourth year of growth, the Trillium seedling will finally produce the characteristic whorl of 3 leaves we are familiar with. Now the real waiting game begins. Growing for such a short period of time each year and often in shady conditions, Trilliums must bide their time before enough energy is saved up to produce a flower. In an optimal setting, it can take a single Trillium 7 to 8 years to produce a flower. If conditions aren't the best, then it may take upwards of 10 years! Slow and steady wins the race in the genus Trillium. A large population of flowering Trillium could easily be 40 or 50 years old!

Sadly, when you couple this slow lifestyle with their undeniable beauty, you begin to spell disaster for wild trillium populations. A plant that takes that long to germinate and flower isn't the most marketable species for most nurseries and, as a result, Trillium are some of the most frequently poached plants in the wild. Because of their slow growth rate, poached populations rarely recover and small plots of land can quickly be cleared of Trilliums by a few greedy people. Leave wild Trilliums in the wild! 

Further Reading:

http://www.trilliumsunlimited.com/resources/3-1NPJ18-20.pdf

http://www.trilliumresearch.org/

The Vernal Dam Hypothesis

I have already established that spring ephemerals are badasses (http://bit.ly/1CsEtj1) but what I am about to tell you is really going to kick it up a notch...

While offering our native pollinators some much needed food resources along with giving us humans a much needed jolt of life after a long and dreary winter, spring ephemerals like these trout lilies (Erythronium americanum), are important nutrient sinks for forests.

Back in 1978, a guy by the name of Robert Muller put forth a very intriguing idea known as the vernal-dam hypothesis. Basically, he proposed the idea that soil nutrients are heavily leached into waterways during the spring melt and subsequent rains. Where spring ephemerals are present, they act as nutrient sinks, taking up much of the nutrients that would otherwise be lost. The idea was well liked but unfortunately, the important assumptions of this hypothesis were not tested until the last decade or so. Recently, more attention is being paid to this concept and some research is being published that do indeed support his claims!

Though the research does not address whether or not the nutrients really would be lost from the system in the absence of spring ephemerals, it is showing that some species really do serve as nutrient sinks. Trout lily, for instance, is a massive sink for nitrogen and potassium. As they grow they take in more and more. When the warmer summer weather hits and the leaves die back, they then release a lot of nutrients back into soil where vigorously growing plants are ready to take it up. It should be noted that trees will still take in nutrients even before leafing out for the summer. One study even showed that net uptake of nitrogen and potassium by a variety of spring ephemeral species is nearly equal to the net annual losses. I must admit that I did not quite understand what the "losses" are in this particular study but the evidence is tantalizing nonetheless. In one example, nitrogen uptake by ephemerals was 12% of the nitrogen in annual tree litter!

Whether or not it is shown that nutrients taken up by ephemerals would otherwise be loss is, in my opinion, beyond the point. What has been demonstrated in the ability of spring ephemeral species to uptake and store vital forest nutrients suggests major ecosystem benefit! Furthermore, when you consider the fact that mycorrhizal fungi are non-specific in most cases and will bond with many different plant species and then go as far as sharing nutrients among the forest flora, you really start to see a big picture story that has been playing out all over the world for millennia. 

Further Reading:

http://www.jstor.org/discover/10.2307/2937357?uid=3739256&sid=21102213017237

http://iub.edu/~preserve/docs/library/BlankJL_1980.pdf

http://www.jstor.org/discover/10.2307/2425383?uid=3739256&sid=21102213017237

http://link.springer.com/article/10.1007/s00442-002-0958-9#page-1

The Badass Spring Ephemerals

Spring ephemerals and the word "badass" are probably not frequent associates but I am here to argue that they should be.

Spring ephemeral season is here for some and just around the corner for the rest of us. It's my favorite wildflower season and I often go missing in the woods for those first few weeks of spring. It is easy to look at their diminutive size and their ephemeral nature as signs of delicacy but these plants are anything but. In fact, when one examines the intricacies of their lifestyle, they can see that spring ephemerals make most other plants look like total softies.

Spring ephemerals, the designation of which gets blurred depending on who you ask, have to complete most of their life cycle in the early spring before the trees and understory shrubs leaf out and completely take over most of the available light. This is an incredibly tough time to be a plant. Soil temperatures are low, which makes nutrient and water uptake a difficult task, all but the most robust pollinators are still sound asleep, and there is the ever present danger of a hard frost or freak snow storm. These factors have led to some incredible adaptations in all of the species that emerge around this time. Whereas each species has its own methods, there are some generalities that are common throughout.

For the most part, spring ephemerals have two distinct growth phases; epigeous (above ground) and hypogeous (below ground). The hypogeous phase of growth takes place throughout fall and winter. Yes, winter. This is the phase in which the plants put out more roots and develop next season’s buds. This goes on at the expense of nutrients that were stored the previous spring. Once spring arrives and soils begin to warm, the plants enter the epigeous phase of growth where leaves and flowers are produced and reproduction occurs. This is an incredibly short period of time and spring ephemerals are well suited for the task.

Typical growth cycle of many spring ephemerals [Source}

For starters, photosynthetic activity for these species is at its best around 20 °C. Photosynthetic proteins activate very early on so that by the time the leaf is fully expanded, the plant is a powerhouse of carbohydrate production. Photosynthesizing in cool temperatures comes at a cost. Water stress in at this time of year is high. Low soil temperatures make uptake of water difficult and it is strange to note that many species of spring ephemeral have very little root surface area in the form of root hairs. These species, however, have extensive mycorrhizal associations which help assuage this issue.

Nutrient availability is also very limited by low soil temperatures. Chemical reactions that would unlock such nutrients are not efficient at low temperatures. Again, spring ephemerals get around this via their increased mycorrhizal associations. It should be noted that some species such as those belonging to the genus Dicentra, do not have these associations. In this situation, these species do in fact develop extensive root hairs as a coping mechanism. Despite specific adaptations for nutrient uptake, you will rarely find spring ephemerals not growing in deep, nutrient-rich soils.

Again, we must keep in mind that all of this is happening so that the plant can quickly complete what it needs to do in the few weeks before the canopy closes and things heat up. It has been observed that high temperatures are associated with slowed growth in most of these species. As temperatures increase, the plants begin to die back. Another adaptation to this ephemeral lifestyle is an increased ability to recycle nutrients in the leaves. As spring temperatures rise, the plants begin to pull in nutrients and store them in their perennial organs. They also show specific compartmentalization of energy stores. In many species, seed production is fueled solely by energy reserves in the stem. Some underground storage structures then receive nutrients to fuel autumn and winter growth while others receive nutrients to fuel leaf and stem growth in the early spring.

Despite all of these amazing adaptations, life is still no cake walk and growth is painstakingly slow. Many species, like trout lilies (Erythronium spp.), can take upwards of 8 years to flower! 8 years!! Think about that next time you are thinking of harvesting or picking some. Even worse in some areas are white tailed deer. East of the Mississippi their populations have grown to a point in which their foraging threatens the long term survival of many different plant species. Especially hard hit are spring ephemerals as they are the first plants to emerge after a long winter of near starvation. 

I hope this post wakes people up to how truly badass these species really are. As our climate warms, we can only speculate how things are going to change for many of them. Some research suggests that things may get easier whereas others suggest that conditions are going to get harsher. It's anyone's guess at this point. As populations are wiped out due to development or invasive species, we are losing much needed genetic diversity and corridors for gene transfer. This is yet another reason why land conservation efforts are so vital to resilient ecosystems. Support your local land conservancy today!

Spring is here and things are getting underway. Get out there and enjoy the heck out of the spring ephemerals! In a few short weeks they will be back underground, awaiting the next cold, damp spring.

Further Reading: [1] [2]