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Parasitic plants of New York.

Like a climax scene from an old, grainy, horror film, the stubby, waxlike "fingers" slowly penetrate the duff on the forest floor, as if someone, or something was buried here, but not quite deeply enough. This plant's habit of resembling the unburied hand of a dead person has given rise to several fascinating, yet macabre names, including "dead man's fingers," and "corpse plant."

Over time, this relatively common, yet altogether strange plant has earned several other common names, including "ice plant," due to the waxy-white appearance of its stem, almost devoid of leaves; and "convulsion weed" from its apparent ability to cause vomiting if ingested, first discovered by Native Americans. But it's most well-known name is Indian pipe, a reference to its rather striking resemblance to an Indian peace pipe. Even its Latin name (Monotropa uniflora) is descriptive, meaning "one turn, one flower," highlighting the fact the lone nodding flower turns upward after pollination.

But what makes Indian pipe look this way? And why is it so different from many other plants?

Unless you are a mycologist who studies fungi, or a plant ecologist, you may not know about the intricate tussles that go on just underneath the soil's surface. There, plants and fungi are locked in battle: competing for resources and nutrients on a tiny, but ubiquitous scale. And while the battle rages, some plants sit on the sidelines, waiting for an opening. Welcome to the gritty underworld of parasitic plants.

A fascinating plant in its own right, the Indian pipe doesn't have even a smidgen of the food-producing, green pigment chlorophyll anywhere to be seen in the plant. So how does it gain the necessary energy to survive since it can't produce its own food through photosynthesis? Well, Indian pipe derives its nutrients and minerals from an outside source, meaning the plant, like a tapeworm or head lice, is parasitic. And there are more than three thousand species of parasitic plants worldwide.

In the case of Indian pipe, the plant taps into the abundant strands of fungal hyphae (branching filaments) that form a dense and interwoven network in most forest soils. These mycorrhizal fungi, notably those strands that produce the common and familiar Russula and Lactarius mushrooms, tie into the roots of trees, mostly oaks, gaining nutrients from the trees. Indian pipe turns the table on them by tapping into their filamentous hyphae made nutrient-rich by their exploitation of the tree.

How was this intimately interwoven subterranean relationship revealed? Through experiments using radioactive carbon dioxide gas. Plastic bags were placed around leaves and radioactive gas was injected into the bag. This gas, a basic ingredient that drives the photosynthetic process, is readily assimilated by the tree. The carbon works its way into the wood and downward to the roots where it is captured first by the fungus and then by the Indian pipe, a fact confirmed by measuring the radioactivity levels in the plant.

There are a few additional species of parasitic plants found in New York's forests that employ the same indirect way of gaining nutrients by using mycorrhizal fungi as an intermediate. One of these is pinesap (Hypopitys monotropa), a close relative of Indian pipe. As the name suggests, pinesap taps into fungi that have tapped into pine trees. Its appearance is similar to Indian pipe; the main difference being that pinesap has multiple flowers per stem (as few as two to as many as twelve), and is pale yellow or cream in color compared to the ghost white of Indian pipe. A similar-looking red plant is known as red or hairy pinesap, Hypopitys lanuginosa. The specific name hypopithys means "beneath the pines," the type of habitat in which the plant is almost always found.

Other parasitic plants tap directly into their host plants through the use of a modified root tip known as a haustorium. The haustorium penetrates the roots of the host plant, intertwining and interconnecting with them to absorb water and nutrients (mostly carbon).

A mid-summer to late-autumn walk through a beech forest will often reveal a common-to-abundant parasitic wildflower that taps into the roots of beech trees, scattered in clumps throughout the forest floor. Known as beechdrops (Epifagus virginiana), with slender stems that rise as high as a foot above the leaves, its Latin name means "growing upon beech," an apt description of this plant's strategy. If you take a moment to look closely at a beechdrops plant, you'll see the pretty tan-and-purple striped tubular flowers emanating from a light-brown colored stem. In coloration, they resemble tiny candy canes.

Beechdrops has a more robust-looking cousin growing in the same mixed deciduous forests of New York: squawroot (Conopholis americana). Also referred to as bear corn, squawroot is a parasite of oaks. It was used by Native Americans for a variety of medicinal purposes, including treatment for menopause.

Another related parasitic species which has arguably the most beautiful flower is the one-flowered broomrape (Orobanche uniflora), also known as cancer-root. It has a white five-petaled flower with fine pink lines in the petals. It is widespread in the state.

Beechdrops, squawroot and one-flowered broomrape are members of the broomrape family, a cosmopolitan group of plants which in some parts of the world are serious agricultural pests, parasitizing important food crops. Affected crops include tomatoes, potatoes, celery, carrots, cabbage, eggplant and various bean species. In severe outbreaks they can cause total crop loss. Significant agricultural losses occur in the countries around the Mediterranean Sea, parts of the Middle East, and Australia. The family name broomrape refers to a tuber or 'rapum', which grows on species of broom, a plant found commonly in Great Britain and throughout Europe.

The orchid family has a few parasitic plants of its own in the form of the genus Corallorhiza, a group of species known as the coralroots, so named because their rhizomes or root masses are shaped like small clumps of coral. The most widespread species of coralroot in New York's forests is the autumn coralroot (Corallorhiza odontorhiza). This plant parasitizes mycorrhizal fungi of several well-known species, including mushrooms belonging to the genus Russula.

Not all parasitic plants tap into their host underground through the intricately interwoven complex of roots, rootlets, hyphae and mycelium. Two plants that take a different approach are the dodders and dwarf mistletoe. Dodder, a member of the morning glory family, is a flowering vine of which there are about nine species native to New York. Its most distinctive trait is its threadlike stem, which has given rise to some of its common names: hairweed, lady's laces, wizard's net, goldthread, angel hair, witches' hair, devil's hair, pull-down, strangleweed, and my favorite: devil's guts.

A dodder plant starts out like other plants. A seed lands in suitable soil and germinates. The shoot grows upward, but in the case of dodder it isn't growing toward sunlight nor expending energy setting roots. Rather, it elongates and using chemosensory clues, which remarkably involves being able to detect volatile organic chemicals emitted from suitable host plants, it grows in their direction.

Once a dodder plant makes contact with a host, it quickly coils repeatedly around the stem, and through the use of numerous haustoria, penetrates the plant. This anchors the dodder. At this point, the vine is no longer connected to the soil. It gains all its sustenance from its host and continues to entangle and intertwine with adjacent plants. Over time, the scene looks a bit like an unhappy chef tossed a large bowl of cooked angel-hair pasta onto a meadow of wildflowers!

New York's one native mistletoe, dwarf mistletoe (Arceuthobium pusillum), takes a different tack. This species is able to invade the vascular tissue of its host (primarily black spruce) through its branches, invading the tree's xylem (for upward movement) and phloem (for downward movement) to gain the nutrients and water it needs. This attack causes the tree to produce a dense packet of branches referred to as "witches' brooms," which are quite noticeable during a forest hike.

How does the mistletoe succeed in colonizing branches? By using two ingenious adaptations, both relating to its seeds. The seeds are dispersed under pressure, exploding from the fruit at speeds as fast as 50 mph. This enables mistletoe to disperse seeds upward onto nearby tree branches. The seeds' sticky coating makes it more likely they'll adhere to the surface they've contacted.

Whether looking for "dead man's fingers" arising from the ground, bowls of "pasta" adorning meadow flowers, or mistletoe's "brooms of witches" amidst the branches in the forest canopy, New York's parasitic plants are an interesting and unique part of our flora.

Retired as the Director of Environmental Protection for the Town of Brookhaven, John Turner also teaches at Stony Brook University. He was a co-founder of the Long Island Pine Barrens Society, and recipient of Newsday's "Everyday Hero" award. John runs a natural history tour company called Alula Birding.


Please note: Some tables or figures were omitted from this article.
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Author:Turner, John L.
Publication:New York State Conservationist
Geographic Code:1U2NY
Date:Aug 1, 2016
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