Biatoropsis usnearum

Biatoropsis usnearum is a species of parasitic fungus that grows exclusively on lichen species of the genus Usnea, particularly U. subfloridana, U. barbata, and U. florida. First described in 1934 by Veli Räsänen, it has become a significant model organism in fungal evolution studies due to its specialised host relationships. The fungus belongs to the order Tremellales, though its precise family classification remains uncertain. It forms distinctive swellings or galls on its host lichens, ranging in colour from pale pink to dark reddish-brown, and notably suppresses the production of host defensive compounds like usnic acid. While initially misclassified due to its unusual characteristics, modern microscopic and genetic studies have revealed it to be part of a species complex, with at least three additional species now recognised. Found across Europe and North America, B. usnearum preferentially infects young, growing parts of its host lichens, particularly branch tips and small branch......read more on Wikipedia.