Arthoniaceae

The family was circumscribed by Heinrich Gottlieb Ludwig Reichenbach in 1841. The process of splitting Arthonia into monophyletic groups is an ongoing process. In order to make Arthonia monophyletic, several genera have been described or resurrected. ==Description==

The family Arthoniaceae consists of lichens that are either lichenized or lichenicolous (living on other lichens), and sometimes lose their lichenized nature. The main body of these lichens, known as the thallus, is crustose, meaning it forms a crust-like appearance on the surface it inhabits. In lichen-forming species of Arthoniaceae, the primary photosynthetic partner (the ), is usually a green alga from the genus Trentepohlia. Occasionally, they associate with other green algae, like Chrosonothrix. The form of the reproductive structures (ascomata) varies widely within this family. They can be (open and -like), (elongated and furrowed), or scattered. Some genera, like Tylophoron, have a unique type of ascomata called . Typically, these structures lack distinct margins made of their own tissue () or host tissue (). The internal structure of the ascomata, known as the , consists of branched and interconnected filaments called paraphyses. In some genera, such as Cryptothecia and Stirtonia, the hamathecium lacks a gelatinous matrix, while in others, like Arthothelium, it is densely packed, resembling a different type of fungal reproductive structure known as ascolocular ascomata. These structures can react to iodine (amyloid reaction) in various ways: not at all (non-amyloid), partially (hemiamyloid), or fully (amyloid). The asci, which are the spore-producing cells, are typically , meaning they have a double wall that splits during spore release. They come in various shapes, from club-shaped () to sac-like (saccate) or even spherical (), and contain a specialized cap structure (apical ) and an eye-like feature (ocular chamber). The asci may react to iodine in different ways: non-amyloid, hemiamyloid, or amyloid. The spores produced by the asci, the ascospores, usually number eight per ascus but can sometimes be fewer, ranging from two to four or even one. These spores are segmented (transversely septate) or have multiple compartments (), with shapes ranging from ellipsoid to clavate. Often, one end of the spore is larger (macrocephalic), or in muriform spores, there is a single large cell. The spores are typically transparent (hyaline) or brown and do not react to iodine. Arthoniaceae also produce asexual spores in structures called pycnidia, and less commonly in . The conidia (asexual spores) can vary in shape from simple, non-segmented forms to those with transverse segments, and can be oblong, rod-like (), needle-like (-), or sickle-shaped (), and are typically hyaline. The family produces a diverse range of secondary metabolites (lichen products), including depsides, depsidones, anthraquinones, and derivatives of pulvinic acid. Some species also contain xanthones. ==Distribution==

The species in Arthoniaceae have a worldwide distribution, but are especially prevalent in tropical areas with a Mediterranean climate. They are known from arctic to tropical latitudes, as well as variating altitudes from sea level to alpine regions, distributed in both humid forests and dry habitats. ==Ecology==

Collectively, the family have a highly variable ecology with lichen-forming, lichenicolous and saprobic fungi. Other species are lichenicolous (growing on other lichens), and a few species, such as those in genus Naevia, are known to be saprobic. ==Genera==

specimen of Arthonia radiata (magnified 40x) showing roughly star-shaped clusters of ascomata. Found growing on the bark of red oak. , Species Fungorum accepts 25 genera and 392 species in the family Arthoniaceae. This is a list of the genera in the Arthoniaceae based on a 2020 review and summary of fungal classification by Wijayawardene and colleagues. Following the genus name is the taxonomic authority (those who first circumscribed the genus; standardized author abbreviations are used), year of publication, and the number of species: • Amazonomyces – 3 spp. • Arthonia – ca. 50 + ca. 300 orphaned spp. • Arthothelium – 10 + ca. 100 orphaned spp. • Briancoppinsia – 1 sp. • Coniangium – 4 spp. • Coniarthonia – 12 spp. • Coniocarpon – 6 spp. • Crypthonia – 16 spp. • Cryptophaea – 1 spp. • Cryptothecia – ca. 65 • Diarthonis – 1 sp. • Eremothecella – 8 spp. • Glomerulophoron – 2 spp. • Helicobolomyces – 2 spp. • Herpothallon – ca. 50 • Inoderma – 4 spp. • Leprantha – 1 sp. • Myriostigma – 7 spp. • Naevia – 3 spp. • Pachnolepia – 2 spp. • Reichlingia – 4 spp. • Snippocia – 1 sp. • Sporodophoron – 4 spp. • Staurospora – 1 sp. • Stirtonia – ca. 25 spp. • Tylophoron – 11 spp. ==References==