The Secret Life of Parasitic Plants

“Parasite” has a bad connotation. There is something unsettling and a little mysterious about an organism that taps into another to survive. But for me parasitic plants mean beauty and balance … and still a bit of mystery.

A little background about parasitic plants: they can be classified as holoparasites or hemiparasites. Holoparasites don’t produce any chlorophyll and rely on their host plants 100% to get the nutrients they need to survive. It is easy to mistake holoparasites, like the Indian Pipe below, for mushrooms because they are often white or pale-colored. Since they don’t need direct sunlight to survive, holoparasites keep most of the plant structure below ground, only sending flowering stalks aboveground to be pollinated and to disperse seeds. So if you see parasitic plant, it’s a special treat!

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Indian Pipe, Monotropa uniflora, is often mistaken for a mushroom because it lacks chlorophyll.

On the contrary, hemiparasites are still completely green and only derive some of their nutrition from their host plant. Indian paintbrush and mistletoes are hemiparasites you might recognize. Parasitic plants tap into their host plant using a special structure called a haustorium. Check out this link to learn more about parasitic plants.

Why do parasitic plants make me think of balance and beauty? If you’ve ever grown native plants in your garden, you probably noticed that often what seem to be well-behaved plants in your favorite meadow become tall, aggressive, spreading giants! Without the rich, complex connections of an intact natural community, these plants grow like crazy. When I see parasitic plants, it is a sign of the intricate web of connections, above and beneath the soil, among the plants, fungi, insects, birds, mammals, herps, bacteria, and other organisms.

Check out the pictures of more parasitic plants you might see in our Oakland Township parks. Enjoy!

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Cancer root, Orobanche uniflora, growing amid a bed of green violet and aster leaves.

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Common Dodder, Cuscuta gronovii, growing on joe-pye and Canada goldenrod. Dodder taps in to the stem of its host plant, not the root.

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Oaks are the only known host plant for Squaw-Root, Conopholis americana.

How can a plant grow if it isn’t green?

If you’re out in the woods this summer, you might notice some plants that aren’t green! How can this be? Plants are supposed to be green! At first you might that you’ve found a fungus, but with a closer look you may notice flowers! Fungi don’t have flowers, so we can rule them out. A few plants are white, yellow, or orange because they don’t have chlorophyll, the pigment that makes plants look green. Instead of harvesting energy from the sun, these plants get their nutrients either from other plants or from the fungal network in the soil, so we call them “parasitic” plants.

Two parasitic plants you might find in the parks this summer are bear corn and common dodder. You might also find Indian pipe (I don’t have any pictures of it yet, but if I find some I’ll post them).

Bear Corn. Also called squaw-root or cancer root (Conopholis americana), this plant grows in woodlands. The only known host of bear corn is oak, so if you find bear corn there must be an oak somewhere in the area. Bear corn looks like a pine cone or a corn cob sticking up out of the leaves.

Squaw-root (Conopholis americana)

Bear corn, also known as squaw-root or cancer root (Conopholis americana).

Common Dodder. If you’re wandering around an open field or wetland, you might stumble upon a mass or orange threads sprawled all over the plants. This parasitic plant is called dodder. We have 9 dodder (Cuscuta) species in Michigan. Our most common species is called common dodder or swamp dodder (Cuscuta gronovii). It can grow on many different hosts. Our species of dodder are annual plants, which means that they only grow one year. The seedlings sprout in the spring, and if they do not find a suitable host they die. If they do find a host, they grow special roots (haustoria) that tap into the host to suck out water and nutrients. You’ll find the little white dodder flowers in July and August.

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The dodder in this picture is the orange threads twined around a goldenrod. If you look closely, you’ll see the little white flowers on the orange stems. The dodder gets all of its water and nutrients from the host plant.

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This dodder is growing on Joe-Pye Weed, a common wetland plant. The little clusters are the flowers that are still in bud, getting ready to open.