A Parasite on a Fungus
Deep in the leaf litter of Chile's temperate rainforests, a pale, leafless stalk emerges, bearing a single, unusual flower. This is Arachnitis uniflora, a plant that lives a life of deception. Lacking chlorophyll, it cannot perform photosynthesis. It is a mycoheterotroph, a type of parasite that steals its food from fungi. Specifically, it targets arbuscular mycorrhizal fungi from the Glomeraceae family. These fungi form symbiotic relationships with the roots of surrounding photosynthetic trees, such as the southern beeches of the genus Nothofagus. Arachnitis taps into this network, siphoning off carbon and nutrients that the fungus has acquired from its tree partner.
The plant spends almost its entire life underground. Its name, Arachnitis, derives from its root system—a cluster of tuberous, branching rhizomes that resembles a spider or a web. These whitish tubers, typically 4 to 17 in number, are small, measuring only 5 to 10 millimeters long. From this subterranean network, a single, unbranched stem, from 6 to 40 centimeters tall, ascends. The stem, which can be whitish, yellowish, or purple, supports a solitary flower—the reason for its species name, uniflora. The flower has six tepals (petal-like structures). Five are long and thin, while the sixth, the median outer tepal, is broad, concave, and marked with 11 to 13 violet nerves.
A Botanical Enigma
The classification of Arachnitis uniflora has long been a subject of botanical debate. Its unusual, non-photosynthetic lifestyle and distinct morphology make it difficult to place in the family tree of plants. Initially, it was grouped with the family Burmanniaceae, but it is now generally placed in the small family Corsiaceae. Even within this family, its relationships are not fully resolved. Molecular studies aiming to pinpoint its closest relatives have yielded conflicting data. Some DNA evidence suggests an affiliation with the order Liliales, which includes lilies and their relatives, but its exact position remains a puzzle. This uncertainty gives it the status of a taxonomic orphan.
Arachnitis uniflora grows in the damp, deep shade of the Valdivian temperate rainforests. Its known range extends along the Andes from southern Peru down to Patagonia and includes populations in the Falkland Islands. The plant's reliance on a specific fungal network and shaded, humid conditions restricts it to these specialized forest floor habitats. The visible flower is ephemeral, but the underground rhizome system is perennial, waiting for the right conditions to send up its strange, solitary bloom.