Heterodermia is a genus of foliose lichens in the family Physciaceae. The genus has a widespread distribution, especially in tropical regions, and contains about 70 species. Heterodermia was historically confused with the related genus Anaptychia, but was distinguished in 1965 based on differences in spore structure and chemical composition. These lichens can be identified in the field using simple chemical spot tests that produce distinctive colour changes when applied to the thallus. The lichens in this genus are small- to medium-sized, usually pale grey in colour, comprising narrow lobes with widened tips fringed with cilia. The lichens can be identified by their thick-walled ascospores and the presence of specific chemical compounds (lichen products) that produce colour reactions when spot tested. Most species are found in tropical and subtropical regions around the world, commonly growing on tree bark in mountain forests. Heterodermia species support a rich community of specialized parasitic fungi, with over 20 different species known to grow specifically on these lichens. Some species have traditional uses in medicine and cooking, particularly in India, Nepal, and Brazil.
Taxonomy
According to Fernanda de Souza and colleagues, the first scientific study of the genus began in 1847 when Thomas Taylor described Parmelia diademata, a lichen that would eventually end up classified as a species of Heterodermia. The genus was formally circumscribed in 1868 by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon. The generic name, which combines the Greek heteros (other, different) and derma (a skin or hide), refers to the presence or absence of a lower cortex.
Prior to this classification, Heterodermia species were placed in genus Anaptychia, an idea proposed by Syo Kurokawa in his 1962 monograph on the genus, until some studies showed that the presence of thick-walled spores and the presence of atranorin could be used as characters to separate the...
