Parasitic Flowering Plants of Appalachia
By Daniel Manget
In late summer in the Southern Appalachians, the plants get so thick that traveling through the woods on anything other than a trail is almost out of the question. The competition for sunlight among the plants has gotten so fierce, and the desire to not be eaten by pests has gotten so strong, that plants are pulling every trick out of the bag in order to spread their seed before winter. A specific group of plants need not worry about such matters of sunlight due to the dramatic evolutionary changes they have gone through. Worldwide there are over 3000 plants that have figured out a way to not have to get their food from photosynthesis. Almost all of them are parasites that exploit the earnings of other decent hard-working photosynthesizing plants. Its a plant-eat-plant world out there.
There are two main categories of parasitic plants; stem parasites and root parasites. Stem parasites puncture into the stem of the host plant with small protrusions and take nutrients directly out of the Xylem and Phloem. They grow out of the ground similar to a vine but eventually detach from the ground completely as it gets enough nutrients from it’s host. Most of the obligate parasitic plants in our region, ones that must parasitize to reproduce, belong to the Broomrape family, Orobanchaceae.
The root parasites are fascinating plants due to their bizarre appearance, and were previously classified as either mushrooms or as saprophytic plants (decomposers) until their underground exploitation was discovered. Almost 90% of plant species can or desire to develop a symbiotic relationship with an fungus called Mycorrhizae (“Myco” meaning fungus “Rhizae” meaning root). This fungus helps plants to absorb decomposing nutrients from the soil, that it couldn’t do on its own, and in return the fungus gets energy from the tree’s photosynthesis. It is a very important relationship in which some Mycorrhizae actually live inside the root cells of the host and others just attach to the root system to take what it needs. Root parasitic plants exploit this symbiotic relationship by creating a (uninvited) menage-a-trios with the fungus and the tree by tricking the fungus into passing energy on from itself and it’s host tree. So the plants are actually parasites of the fungus and not the tree directly, exploiting their friendly and generous relationship. All Orchids have a relationship with Mycorrhizae but they only use it to supplement the food they already get from photosynthesis. Having this partnership is why Orchids are one of the most widely spread plant families on earth.
Here are some plant root parasites that are common to the southern Appalachians:
The most common parasitic plant found in the Appalachian region is usually thought to be a mushroom from its appearance. It’s most commonly called Indian Pipes, Monotropa uniflora, but is also refereed to as the ghost plant, ghost pipes, corpse plant, and anything else that might explain its odd ghostly white complexion. It comes out of the ground with the “pipe” part pointing down but, once the flower has been pollinated, the “pipe” part points upward and grows a seed within.
A closely related plant is called Pinesap, Monotropa hypopitys, has a very similar relationship to Mycorrhizae and the tree host. It is called Pinesap because it is usually found in woods dominated by pine.
Another root-parasitic plant is called Beech Drops, Epifagus virginiana, and only forms parasitic relationships with the Mycorrizae of Beech trees.
Conopholis americana, also known as Squaw Root or Bear Corn or Cancer root, is a very strange looking parasitic plant indeed. A favorite food source of bears, this plant takes nutrients from a fungus attached to the roots of any tree in the Beech family (Oaks especially). After the plant goes to seed you can still see the black cones jutting out of the forest floor throughout the summer.
Now for the stem parasites:
Common dodder, Cuscuta gronovii, is a fascinating plant for botanists and a serious nuisance for farmers. Like it’s distant root parasite cousins, it is an obligatory parasite because it can’t exist without a host. It grows out of the ground, like a vine, near a host but is bright yellow due to it’s lack of chlorophyll. It slowly grows upward around the stem of it’s host and sticks little nodules (haustoria) into the cells of the stem. Once it starts getting nutrients from its host, the roots and base of the plant withers and dies because that part of the plant is no longer needed. It’s now getting everything it needs from its host.
Next time you catch yourself standing under a Mistletoe around the holiday season, you should grab the closest person and steal a kiss and then their wallet. After all, that is what the Eastern Mistletoe, Phoradendron serotinum, is doing to its Oak Tree (or sometimes coniferous) host, exploiting the hard work of another plant. Mistletoe is different from the other parasites we’ve discussed because it is green and therefore has chlorophyll and can make it’s own food. However, since it grows in the upper branches of it’s host, it needs to steal the water and minerals that it can’t get from the soil. Like Dodder, the Mistletoe punctures through the bark layer of the tree with many Haustoria and takes what it needs. Funny how the traditions of the Mistletoe are so fitting for the plant’s ecology.
If you’re hiking in the woods, take a closer look at what you might think is a mushroom because it may be one of these rare and peculiar parasitic flowering plants.
Agerer, R. 2006. Fungal relationships and structural identity of their ectomycorrhizae. Mycological Progress 5: 67-107.
Ashford AE, Allaway WG, Peterson CA, Cairney JWG. 1989. Nutrient transfer and the fungus-root interface.Australian Journal of Plant Physiology 16: 85-97.
Nickrent, D.L. and Musselman, L.J. 2004. Introduction to Parasitic Flowering Plants. The Plant Health Instructor. DOI: 10.1094/PHI-I-2004-0330-01