#herbivory

Drought Tolerant Plants: Blue Flax

“Lewis’s prairie flax is a pretty garden ornamental suited to hot, dry sites. Each morning delicate sky blue flowers open on slender arching stems, only to fall off in the afternoon and be replaced by others the next morning. In spite of its fragile appearance, it is quite sturdy and may put out a second flush of blossoms on new growth in late summer.” — Common to the This Country: Botanical…

Observations of a Mount Rainier Plant Ecologist

It's skunk cabbage (and Trillium) season in Longmire! Yellow skunk cabbage (Lysichiton americanus) flowers emerge before the leaves just after snow melt in wet areas. The species is related to the Corpse plant (Titan arum) and produces a fetid odor from the many small flowers on its columnar spadix (the yellow spike) to attract flies and beetles. Despite the smell and potentially high quantities of oxalic acid, deer in the park seem to be munching on some flowering shoots before they can fully emerge. 

Biologists have several theories about why deer can eat potentially toxic plants. It could be that a deer’s wide diet of different plants diminishes the effects of toxins. Researchers have also found that deer will lick clay or minerals from the soil that can bind toxins and counteract the effects. It could also be their gut chemistry. Deer, similar to cows, have symbiotic bacteria in their rumen-reticulum (the first two of their four multiple stomachs) that help them break down and digest the vegetation they eat. Whatever the reason, deer can eat a lot of plants that people can not! 

We've all been there at some point. It's summer, it's a beautiful day, and you find yourself strolling along a trail. You are walking along, enjoying the sights, sounds, and smells of your environment when you harmlessly brush by a patch of waist-high plants. You don't think anything of it. They are herbaceous and don't readily catch the eye. A few steps later and the burning starts. It is mild at first but wherever your skin met the tissues of those plants an itchy, burning sensation starts to amplify. You have likely just encountered a species of stinging nettle. 

Nettles hail from a handful of genera. There are many different species of nettle but you are most likely to encounter either stinging nettle (Urtica dioica) or the wood nettle (Laportea canadensis), all of which belong to the nettle family (Urticaceae). A closer inspection of the plant reveals that the stems as well as the underside of the leaves are covered in tiny hairs. These hairs are called trichomes. A subset of these trichomes are what caused your discomfort. 

These trichomes have been honed by natural selection into a very effective defense. They are an elongated cell that sits atop of a multicellular pedestal. They are quite brittle and any contact with them causes their tips to break. They are also hollow and once they are broken, they essentially function like mini hypodermic needles. They penetrate the skin of any animal unlucky enough to brush up against them and inject an irritating fluid into the tissues of their "attacker." The fluid itself is quite interesting. Chemical analyses have revealed that it consists of a complex mixture of histamines, acetylcholine, serotonin, and even formic acid. Chemists are still working out the exact makeup of this chemical weapon and how much variation there is between different stinging species. 

As you might have deduced by this point, these stinging hairs are a defense mechanism. They protect the plant from herbivores. However, not all herbivores are deterred by this defense. It was found that invertebrates don't seem to have any issue navigating the stinging hairs. Instead, it is thought that the stinging nature of these plants evolved in response to large mammalian herbivores. This makes some sense as larger herbivores pose more of a threat to the entire plant than do invertebrates.

Even more interesting is the response of some nettles to varying levels of herbivory. It has been found that heavily damaged plants will regrow leaves and stems with higher densities of stinging hairs than those of plants that have experienced lower rates of herbivory. This too makes a lot of sense. Stinging hairs require resources to produce so plants that have not experienced high rates of herbivory do not bother allocating precious resources to their production.

Even more interesting is the fact that for stinging nettle (U. dioica), male and female plants tend to have differing densities of stinging hairs. Female plants produce more stinging hairs than males. It is thought that since females must invest more resources into producing seeds than males do into producing pollen, they must also invest in more protection for these valuable reproductive assets. 

These nettles are not alone in producing such stinging trichomes. Many other plant species have converged on this defensive strategy. If you have ever experienced this for yourself, you can really understand just how effective it can be. 

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

Drought Tolerant Plants: Yellowhorn

A drought tolerant garden doesn’t have to be treeless. While the pickings are slim, there is a selection of trees that, once established, are well adapted to deal with extended bouts of little to no water. One such tree is yellowhorn, a species that demands to be considered for any waterwise landscape. Yellowhorn is rare in cultivation – and also restricted in its natural distribution – but…

Death by Crab Spider, part two

Crab spiders that hunt in flowers prey on pollinating insects. Thus, pollinating insects tend to avoid flowers that harbor crab spiders. We established this in part one. Now we ask, what effect, if any, does this interaction have on a crab spider infested plant’s ability to reproduce? More importantly, what are the evolutionary implications of this relationship?

In a study published in Ecological…

Spend enough time around various Bromeliads and you will undoubtedly notice that some species have a rather gooey inflorescence. Indeed, floral mucilage is a well documented phenomenon within this family, with something like 30 species known to exhibit this trait. It is an odd thing to experience to say the least.

The goo takes on an interesting consistency. It reminds me a bit of finding frog spawn as a kid. Their brightly colored flowers erupt from this gooey coating upon maturity and the seeds of some species actually develop within the slimy coating. Needless to say, the presence of mucilage in these genera has generated some attention. Why do these plants do this?

Some have suggested that it is a type of reward for visiting pollinators. Analysis of the goo revealed that it is 99% water and 1% carbohydrate matrix with no detectable sugars or any other biologically useful compounds. As such, it probably doesn't do much in the way of attracting or rewarding flower visitors. Another hypothesis is that it could offer antimicrobial properties. Bromeliads are most often found in warm, humid climates where fungi and bacteria can really do a number. Again, no antimicrobial compounds were discovered nor did the mucilage show any sort of growth inhibition when placed in bacterial cultures.

It is far more likely that the mucilage offers protection from hungry herbivores. Flowers are everything to a flowering plant. They are, after all, the sexual organs. They take a lot of energy to produce and are often brightly colored, making them prime targets for a meal. Anything that protects the flowers during development would be a boon for any species. Indeed, it appears that the mucilage acts as a physical barrier, protecting the developing flowers and seeds. One study found that flowers protected by mucilage received significantly less damage from weevils than those without mucilage.

The mucilage could also provide another benefit to Bromeliads. Because these plants rely on water stored in the middle of their rosette (the tank, as it is sometimes called), some species may also gain a nutritional benefit as well. Bromeliad flowers emerge from this central tank so anything that gets stuck in the mucilage may eventually end up decomposing in the water. Since nutrients are absorbed along with the water, this could be an added meal for the plant. To date, this has not been confirmed. More work is needed before we can say for sure.

Photo Credit: [1] [2]

As climate change intensifies and human activities alter ecosystems, young oak seedlings face a double threat: drought and hungry herbivores. Normally, we’d think this combination of stresses would be fatal for oaks. But new research published in the Annals of Botany Special Issue on Plant Reproduction in a Changing Global Environment suggests that herbivory could help oak seedlings survive…