The Nature Corner: Poison plants, parasites, predators and hitchhikers
Published 6:42 am Tuesday, August 20, 2019
By Ernie Marshall
I’ve been sprucing up a nature trail by identifying plants with handmade signs at A Time For Science’s site near Grifton. That gave me an opportunity to think about the peculiarities of the Plant Kingdom. Here are a few examples to illustrate.
A number of plants are poisonous to eat. This is presumably a defense against being eaten by animal herbivores of all sorts, including humans. Top of the death list are surely mushrooms of the genus Amanitus, which look harmless enough but deservedly have sinister names such as “death cap” and “destroying angel.” With some plants, only part of the plant is poisonous. A rule of thumb is anything red or purple on pokeberry (especially the berries) is poisonous; and for rhubarb, it is anything green. Pokeberry leaves are used in salads; and the red rhubarb stems make delicious pies.
Species of the genus Toxicodendron, poison ivy, poison oak and poison sumac, are “poisonous” to the touch for 85% of humans (but not for any other species). It is actually an intense allergic reaction of the skin cells to oils produced by the plant.
The noxious plant bears some responsibility for my interest in nature. The summer I was sixteen I worked as a counselor at our Boy Scout Camp. I applied for a position on the swimming and boating dock – time on the water, getting a tan to impress the girls and all that fun stuff. Instead I was assigned teaching nature study. I bunked with one of the three guys doing dock duties. Their first assignment was to cut the vegetation that had grown up since the last camping season and pile it up, burn it and rake it into the water, to wash away.
Folks neglected to observe that much of the vegetation was poison ivy. The dock crew had just been in contact with it and “poisoned” the water in the swimming area to boot. They all came down with a horrible itching, oozing, rash – head to toe misery. Incidentally, the plant oils that produce the contact allergic reaction are not destroyed by fire and are produced by all parts of the plant.
This caused me to reflect that I had missed a bullet with my assignment to lead bleary-eyed campers on crack-of-dawn birding walks and such.
The best known of plant parasites is surely mistletoe. The report on it is more benign than on poison ivy. It is only a partial parasite, taking water from the tree, but not nutrients, and apparently does no real harm to the tree. It photosynthesizes its own food and stays green all year. This is of course part of the reason that it, along with holly and fir trees (also “evergreens”), are midwinter holiday decorations.
The oddity about mistletoe is that it prefers to perch in trees and tap into their water supply (the xylem layer under the bark) rather than just root itself in the ground. Mistletoe has attractive white berries, poisonous to us but a favorite of birds. Hence when birds are not making unwelcome poop deposits on your freshly washed car or laundry, they leave the seeds on tree branches to sprout new mistletoe plants.
Carnivorous plants, as they are called, actually eat animals, albeit small ones such as insects. One of my favorite movies is Little Shop of Horrors (1986) featuring a plant potted in a Maxwell House Coffee can in a small flower shop that develops carnivorous habits, a liking for human blood and grows to a frightening size. Customers begin to disappear. You get the idea. This waking nightmare is modeled on a real plant, the Venus flytrap, one of some 500 species of carnivorous plants around the world.
I have seen Venus flytraps in Croatan National Forest in Carteret County. They are hardly a thing that could frighten anything but a fly, but could be the inspiration for something more ominous. A pair of their leaves are enlarged and hinged like a clam shell so that they can snap shut to capture an insect, which the plant then slowly digests.
Other carnivorous plants use different traps and snares. Sundew plants excrete a glue-like substance in which insects get mired. Pitcher plants are so named because their leaves form a long pitcher-shaped tube that collects rain water in which insects fall in and drown. Slick, steep sides and guard hairs prevent the insect from escaping. Stands of pitcher plants can be easily seen in Pocosin Lakes National Refuge along NC 94 between Hyde and Tyrrell Counties (shortly after crossing the Intracoastal Waterway bridge.) Pitcher plants are also known as “hunters cups” because a thirsty hunter can get a drink of water from the plant. (Just spit out the bugs.)
Carnivorous plants go to all this trouble and ingenuity to catch insects and other small prey, because they live in wetland soils that are deficient in nitrogen, which is essential to plant growth.
What I’m calling “highjackers” are vines. All plants require sunlight as an ingredient for photosynthesis. Other plants ranging in height from small herbaceous plants to the tallest Giant Redwood depend upon what stems, branches, and trunks can support against gravity as they thrust upward seeking the sun. Vines can grow as tall as their supporting host, on which they hitch a ride, so to speak, in their reach for that same light.
Vines just have to figure out how to cling, and they have developed plenty of devices for that. Some, such as morning glories and pole beans, twine around their support. Grape vines, for example, send out tendrils that clasp; and English ivy and poison ivy, send out roots from the sides of their stems that seek crevices.
Nature indeed comes up with ingenious adaptations to survive and even thrive.
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