Scoliciosporum arachnoideum
Scoliciosporum arachnoideum is a bark-dwelling crusty lichen from Madagascar. It forms a pale, white-grey, powdery crust on tree bark, underlain by a visible cobweb-like network of fungal threads. The fruiting bodies are pale ochre and covered with a white frost.
It is known from only one tree in a humid mountain rainforest near Andasibe, at about 950 meters elevation. The lichen was collected in 1984 and described as a new species in 2008 by André Aptroot. The name “arachnoideum” refers to its distinctive cobweb-like tissue.
Although it looks similar to Scoliciosporum pruinosum, S. arachnoideum has darker internal tissue and cobweb margins. Some scientists think it might belong to a different group, possibly Ramalinaceae or even a different genus such as Jarmania.
Key features include a crust-like, whitish-grey thallus that is powdery in appearance, a white hypothallus that can spread over a large area, and a white arachnoid margin. The photosynthetic partner is green algae about 5 μm across. Apothecia are common, small (0.3–0.8 mm), pale ochre with white frost. Spores are colorless, long and corkscrew-shaped, usually three-septate. Chemical tests show a yellow reaction with potassium hydroxide and the presence of atranorin; the pruina comes from an unknown compound.
This species is currently known only from its type locality on one tree in a very wet rainforest, so it may be endemic to Madagascar.
This page was last edited on 3 February 2026, at 08:09 (CET).