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The Ghost Flowers
Growing in quiet obscurity throughout temperate North America are two small, closely related and seldom seen species of flowering plants - the Ghost Flowers - Indian Pipe (Monotropa uniflora) and Pinesap (Monotropa hypopithys). Spending nearly their whole lives underground these two species lack leaves, chlorophyll or even true roots. They surface only when conditions are favorable to bloom. Since they don't require sunlight to survive these plants have lost nearly all their natural color and their flowers, when they appear, are a ghastly, unnatural white - hence the name: Ghost Flower.
Habitat and Classification
While neither are common (or at least commonly seen) both species are found in similar habitats - rich, mature deciduous woodland. Of the two, the fall-blooming Indian Pipe is the more common; while its cousin Pinesap - which appears to have more stringent requirements for its growth - is a truly rare plant. Both have similar lifestyles and - like the completely unrelated Orchid Family - both rely on and require fungi to survive.
When originally discovered it was assumed that they were just (albeit very weird) parasitic plants - and for a number of years they were lumped with other parasites. However this hypothesis was eventually discarded when it was discovered that these supposed parasites lacked true roots and were never found attached to any other plant. Following this discovery they were assumed to be (for lack of any better hypothesis) saprophytes - plants that subsist on the decaying remains of other plants. Of course no one bothered to discover how they managed to perform this neat little trick (especially without true roots) but this notion persisted for years and is still occasionally encountered in textbooks even today.
The truth was far more interesting and complicated than anyone guessed.
The Fungal Connection
Both of our ghost flowers - as recent research has finally proven - are obligate myco-heterotrophs, which is just a botanist's way of saying that they require fungi to gather their food and feed them. So in a sense they are parasites - on fungi. But as with so much of biology this is far too simple an answer. The fungal species that they "parasitize" are mycorhizal fungi and their "parasitism" leads to unexpected effects on their supposed "hosts".
Mycorhizal fungi are those species (and there are thousands - if not millions - of them) that live symbiotically with plants containing chlorophyll. The fungi form dense nets of fungal hairs (Hartig Nets) around the roots of forest, prairie and desert plants and send their threadlike mycelium (mushroom "roots") far afield where they gather nutrients and water. They share these gathered riches with the plants they've partnered with and in exchange the plants give the fungi sugars (that only green plants can produce) so that both organisms thrive far better than either could alone.
While real research into this phenomenon is only beginning science is slowly coming to understand the importance of fungi to the health of global ecosystems. So far 98% of the plants investigated for mycorhizal symbionts have proven to have them. In fact, in the Pacific Northwest, Douglas Firs and other valuable timber trees have been shown to require these fungal symbionts to live. Trees lacking them, or those grown under sterile laboratory conditions, quickly sicken and die if their fungal partners are absent or lacking. Some species of grass actually have the fungus inside their tissues. And everything from wheatfields, oak trees and carrots to the humble Ghost Flowers require the presence of these fungi to grow their best.
Green plants pay their way with their fungal symbionts by providing sugars and other nutrients that the fungi themselves are unable to manufacture for themselves. Since the Ghost Flowers lack chlorophyll but still obtain nutrients from their fungal partners it appears that they are parasites in the classic sense - organisms that take without returning anything to the partnership - indirectly parasitizing the trees that partner with the fungus.
But recent research in Japan and California is upsetting this simplistic view. Scientists studying plants with habits identical to our Ghost Flowers have discovered that these supposed parasites have a beneficial effect on the fungi they supposedly parasitize by increasing their numbers in the soil. No one yet has any conclusive evidence as to how they do this (though it's almost certainly chemical), but fungal populations surrounding these plants are orders of magnitude higher than they are just a few yards away. The data shows that these fungus-eating plants that lack chlorophyll stimulate their fungal partners into increased growth and higher populations thereby promoting higher nutrient uptake in the trees that are symbiotically attached to the fungus. In short the tree benefits by getting more nutrients than it ordinarily would, the fungi benefit from higher populations than they would ordinarily attain and the supposed "parasites" feast on a percentage of the surplus they themselves create. Our Ghost flowers turn out to be tiny (if complicated) fertilizer factories!
In the Grand Scheme of Things our Ghost Flowers are pretty insignificant and it's certain that trees and forests would survive without their continued presence, but they're interesting, unusual and fascinating organisms. And while our ignorance concerning these amazing and highly specialized little plants is almost total they do teach us the importance of not jumping to conclusions about the organisms sharing our world and their place in it, since nearly every past assumption made about these little guys has been absolutely wrong.
The information on this page is tailored to Southern Illinois, Southwest Indiana, Western Kentucky, and Southeast Missouri
Copyright © 2004 Jim Jung
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