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.

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