Ghost plant, Monotropa uniflora, is now flowering in shaded woodlands. The species is also known as Indian pipe or corpse plant. Each stem is about finger-high and has a nodding flower at its tip. The plant’s pallor tells the story of its peculiar feeding methods. Rather than using pigments to gather sunlight, the roots are sheathed with fungi from whom the plant gets its food. Monotropa is quite specialized, connecting to a small number of Russula fungi species. The fungi in turn feed themselves by tapping the roots of trees, so Monotropa is indirectly feeding from other plants, using a fungus as the money-laundering intermediary. Whether the fungus gets anything in return from Monotropa is not known. The plant is usually regarded as wholly parasitic.
Monotropa belongs to the Ericaceae plant family, a group that includes heathers, blueberries, rhododendron, and sourwood. These species often live on nutrient-poor acid soil where symbiotic relationships with fungi help the plants to thrive in conditions that are otherwise hostile to roots. Monotropa also favors acidic areas and is often found in deep shade under conifers. It seems that Monotropa took its family heritage and changed it from mutualism to piracy. If so, this is the genus that no-one likes to discuss at the Ericaceae family reunion. Quite why the fungus would put up with its parasite is a mystery. It could be that the evolution of defensive mechanisms has not happened because the tiny Monotropa plant draws so little food compared to the supply that the fungus receives from trees. It is perhaps no coincidence that nearly all non-parasitic Ericaceae plants are shrubs and trees, and only Monotropa is a tiny sprout. The plant’s narrow range of fungal associates may also indicate that only a few fungus species can be fooled. All this has conservation implications: Chris Martine and Alison Hale have recently published a fascinating article suggesting that chemicals from invasive plants such as garlic mustard may disrupt the relationships between Monotropa and its fungi, causing population declines.
The species lives in North America, Asia, and Central America, with large geographic gaps between each population. Recent studies of DNA show that these populations have diverged from one another and have distinctive genetic signatures, suggesting that they might best be regarded as different species. How the species came to have such a distribution is unknown: the dust-like, winged seeds may have traveled by wind or the distribution may be an echo of the ancient geographic connections among these continents.
Five days after the bloom pictured above, pollinating bumblebees have done their work and the red fruit capsules are swelling. The flower’s rain-shedding, bee-welcoming droop has straightened and the fruit points directly to the sky, presumably the better to catch some favorable winds to a neighboring uncolonized fungus, or to Japan.