Arachnitis is a monotypic plant genus in the family Corsiaceae, order Liliales, containing a single species: Arachnitis uniflora Phil. Described by the Chilean botanist Rodolfo Amando Philippi in 1864, it is known by the common name Spider-Flower.
Unlike the vast majority of flowering plants, Arachnitis is entirely non-photosynthetic. It lacks chlorophyll and cannot manufacture its own sugars through photosynthesis. Instead, it is mycoheterotrophic — it parasitizes soil fungi to obtain the carbon it needs to survive. Specifically, it draws carbon from mycorrhizal fungi of the family Glomeraceae that colonize its roots. Although these fungi are in other contexts typical arbuscular mycorrhizal partners for many plants, their relationship with Arachnitis uniflora is unusual: the characteristic structures called arbuscules are absent, distinguishing the association from a standard mutualistic mycorrhiza.
As a member of Corsiaceae, Arachnitis belongs to a small family of achlorophyllous, non-autotrophic monocot herbs. The placement of Arachnitis within Corsiaceae has been debated; some botanical authorities argue it is more closely related to the family Burmanniaceae, which also contains non-photosynthetic mycoheterotrophic plants, though APG II formally places Corsiaceae — and with it Arachnitis — in Liliales. The sole species, Arachnitis uniflora, is native to the southern cone of South America (Bolivia, Chile, and Argentina) and the Falkland Islands, where it grows as a small, inconspicuous herb in the forest understory.
Etymology
The genus name Arachnitis is derived from the Greek arachne (spider), a reference to the spider-like appearance of the plant's flowers or roots. The genus was described by Chilean botanist Rodolfo Amando Philippi in 1864.
Distribution
Arachnitis uniflora is native to southern South America — Bolivia, Chile, and Argentina — as well as the Falkland Islands. With over 460 iNaturalist observations, records are concentrated along the Andes and the Patagonian zone.
Ecology
Arachnitis uniflora is mycoheterotrophic: it obtains all of its carbon by tapping into Glomeraceae fungi in the soil rather than through photosynthesis. Its fungal relationship resembles arbuscular mycorrhizae structurally but lacks arbuscules, making it a distinctive non-mutualistic dependency. The plant grows in forest understory habitats where light is limited — conditions that make a purely heterotrophic nutritional strategy viable.
Taxonomy Notes
The genus Arachnitis was described by R.A. Philippi in 1864 and is placed in family Corsiaceae within order Liliales (APG II). Its position within Corsiaceae has been contested: some authorities cite evidence that Arachnitis is more closely allied with Burmanniaceae than with the other Corsiaceae genera (Corsia and Corsiopsis). GBIF lists the genus as accepted with two descendant taxa.
