Ochrolechia is a genus of crustose lichens in the family Ochrolechiaceae. These lichens typically form uneven, often thick, crust-like growths on various surfaces and are characterised by their white to pale grey thalli, which may have a greenish tint. The genus has a long evolutionary history, with fossils dating back to the Paleogene period, about 34 million years ago. Ochrolechia species have disc-like apothecia (fruiting bodies), which are usually yellowish or brownish-pink and often covered with a fine white powdery coating. The genus is widely distributed and includes both common and rare species, with some found in extreme environments such as arctic and alpine regions. Ochrolechia lichens produce diverse secondary metabolites, including orcinol depsides, depsidones, and xanthones.
Paleontological studies have revealed that Ochrolechia existed as far back as the Paleogene period, approximately 34 million years ago. This discovery was made through the analysis of well-preserved amber fossils from Europe. These fossils include several Ochrolechia specimens that show morphological similarities to modern species, such as O. subplicans and O. xanthostoma. Two of these ancient Ochrolechia specimens were found hosting lichenicolous fungi of the genus Lichenostigma, indicating a long-standing symbiotic relationship between these fungi and their lichen hosts. The presence of such fossils provides calibration points for understanding the evolutionary timeline of both Ochrolechia and Lichenostigma.
The genus Ochrolechia comprises crustose lichens that typically form uneven, often thick, crust-like growths. The thallus, or body, of these lichens can vary in appearance from smooth and continuous to slightly cracked . In some cases, the thallus may appear as scattered, convex warts or, more rarely, as minutely shrubby due to the presence of tiny or spine-like extensions. The colour of the thallus ranges from white or pale grey to dark grey, often with a greenish tint. A, which is a preliminary growth that may be visible around the edges of the thallus, is sometimes present and grey, though it may also be absent.
The upper surface of the thallus generally lacks a distinct protective layer, or may have a very thin cortex made up of thin-walled fungal filaments (hyphae). The lichen's symbiotic partner, or, is a alga, which contributes to the lichen's overall colour and undertakes photosynthesis.
The reproductive structures of Ochrolechia, the, are disc-like and typically expanded, though in rare cases, they may be pore-like . The are usually yellowish or brownish-pink in colour, often covered with a fine white powdery coating known as pruina. The apothecia are surrounded by a well-developed, which is a rim of tissue derived from the thallus itself. In some species, a narrow, the tissue surrounding the hymenium (spore-producing layer), is visible.
The hymenium in Ochrolechia apothecia is relatively tall, measuring between 150–200 μm. The, which supports the developing spores, consists of thin, densely branched, and interconnected filaments known as paraphyses. The asci, or spore-producing cells, contain between two and eight spores, and have thick, amyloid walls, meaning they stain blue with iodine and are similar to those found in the genus Pertusaria. The themselves are relatively large, lack internal divisions, have relatively thin walls considering their size, and are smooth in texture.
Ochrolechia also reproduces asexually through pycnidia, which are flask-shaped structures embedded in the thallus. The conidia (asexual spores) produced by the pycnidia are cylindrical to elongated and are straight rather than curved.
Chemically, Ochrolechia species are known to produce orcinol depsides and depsidones, particularly gyrophoric and lecanoric acids, as well as xanthones and fatty acids. These compounds contribute to the lichen's characteristics and can be used in chemical spot tests to help identify the species.
, Species Fungorum (in the Catalogue of Life) accepts 41 species of Ochrolechia.