Cryptothecia is a genus of white to greenish crustose lichens that grow on bark, wood, or leaves, in tropical or subtropical areas worldwide. It has a conspicuous prothallus that develops around its periphery which can be bright red in some species, hence the common name wreath lichen. The main vegetative body (thallus) lacks a cortex (ecorticate and is often immersed in the substrate or byssoid (whispy, like teased wool). The medulla is white, well defined, and often peppered with calcium oxalate crystals. Ascomata are not well defined, being cushions of soft white mycelium immersed in the medullary tissue, hence the name from the Greek krypto = "to conceal" and theke = "a container or sheath". It contains Trentepohlia, a green alga, as its photobiont partner.
Two species have been described in North America. At least one species, Cryptothecia rubrocincta, has been used in Brazil as a source of dye.
The genus was circumscribed by James Stirton in 1877, with Cryptothecia subnidulans assigned as the type species.
Species in the genus Cryptothecia have a crustose thallus, which can be either immersed in the or its surface. The colour of the thallus ranges from white to greenish, often with a (cottony) texture. Some species have spherical isidia-like , although soredia are absent. The prothallus typically consists of interwoven or radiating hyphae, and the may be either distinct or indistinct. The medulla is usually well-defined, white, and frequently amyloid, often containing numerous colourless calcium oxalate crystals.
Cryptothecia does not have well-defined ascomata (fruiting bodies). Its areas, which can be common or rare, are restricted to cushions of soft white mycelium within the loose medullary tissue. These areas tend to spread over the whole thallus, forming small clusters near the surface or cushion-like structures. Asci are spherical to ovoid, , and thick-walled, typically measuring 60âÂÂ160 by 30âÂÂ130 üm. They are enclosed in a cocoon-like layer and contain 1âÂÂ8 spores. The are , ellipsoidal, and often somewhat curved, ranging from 40âÂÂ110 by 15âÂÂ65 üm in size.
Conidiomata in Cryptothecia are and range from immersed in the substrate to emergent, with a dark brown wall. Conidiogenous cells are , and (rod-shaped) to narrowly (club-shaped_. The conidia are colourless, simple, bacilliform, and range from 3âÂÂ8 by about 1 üm, or they can be thread-like, (threadlike), and multiseptate, measuring 110âÂÂ140 by about 1.5 üm.
, Species Fungorum (in the Catalogue of Life) accepts 53 species of Cryptothecia.