A plant without green
In the deep humus of a conifer forest, a strange, reddish-brown stalk called Pterospora andromedea pushes through the soil. Commonly known as pinedrops, this plant can reach heights of over a meter, or 3.3 feet, and sometimes as tall as two meters. The entire stalk is covered in fine, sticky hairs, giving it a clammy feel. Unlike most plants, pinedrops contain no chlorophyll and cannot perform photosynthesis. Its leaves are reduced to small, scale-like structures, mostly found on the lower part of the unbranched stem.
The upper half of the stalk becomes a raceme of nodding, urn-shaped flowers. These flowers, which appear from June to August, are typically yellowish or white. The plant's scientific name, Pterospora andromedea, reflects its appearance; andromedea was chosen because the flowers resemble those of the genus Andromeda, while Pterospora means "winged seed." After flowering, the stalk dries into a stiff, woody structure that can persist for several years.
The fungal intermediary
The survival strategy of pinedrops is the complex form of parasitism known as mycoheterotrophy. It doesn't steal nutrients directly from pine trees. Instead, it targets fungi that are in a symbiotic, mycorrhizal relationship with the trees. The plant is an epiparasite, forming a three-part chain: the pine tree photosynthesizes, the fungus trades nutrients with the tree for sugars, and the pinedrops plant steals the sugar from the fungus.
This relationship is highly specific. Pterospora andromedea almost exclusively targets fungi from the genus Rhizopogon, which are often called "false truffles." In the western United States, including Wyoming, the primary fungal host is Rhizopogon salebrosus. The plant's roots form a dense, ball-like structure that becomes completely encased by the fungal mycelia. The germination of pinedrops seeds is entirely dependent on the presence of enzymes secreted by a compatible Rhizopogon fungus.
The plant's life is a gamble on finding this specific fungal partner. To increase its odds, a single pinedrop produces an enormous number of seeds. Each fruiting capsule can contain up to 4,800 seeds, and a large plant can produce over 100 capsules. The seeds are minuscule and feature a wing-like tissue that allows them to be dispersed widely by the wind. This strategy of mass production and wind dispersal is necessary for the microscopic seed to land in a location with the precise conditions and the specific fungal partner it needs to grow.