Thamnolia vermicularis

Thamnolia vermicularis, the whiteworm lichen, is the traditional name applied to a widespread, morphologically uniform group of fruticose lichens in the family Icmadophilaceae. The species forms loose mats or scattered tufts of slender, worm-like, chalky-white branches that typically reach up to 5 cm long, growing on tundra terrain across arctic and alpine habitats. It was first described in 1781 by the Swedish botanist Olof Swartz from the alpine regions of Lapland, and the modern scientific name was formalized by Ludwig Schaerer in 1850.

Material traditionally identified as T. vermicularis occurs as two chemotypes distinguished by their chemical composition and ultraviolet fluorescence: one fluoresces yellow under UV light due to squamatic and baeomycesic acids, whereas the other produces thamnolic acid and does not fluoresce. Although these chemotypes were historically treated as separate species or subspecies, they are now generally interpreted as chemical variants, and recent DNA-based work has shown that material long identified as T. vermicularis includes additional, morphologically cryptic species, including T. tundrae in the far north and T. taurica in the European Alps. The UV-positive form is more common in the Northern Hemisphere, whereas the UV-negative form predominates in the Southern Hemisphere.

Thamnolia vermicularis is essentially sterile and reproduces asexually through thallus fragmentation and small spore-producing structures called pycnidia, lacking functional sexual fruiting bodies. Whiteworm lichens identified as T. vermicularis have an extremely broad distribution in cold regions, occurring in arctic and alpine tundra habitats on all continents except Africa and Antarctica, and shows considerable flexibility in its association with photosynthetic green algal partners from the genus Trebouxia. In traditional Chinese medicine, the species is used as a component of 'snow tea' (xuecha).