The Graphidaceae are a family of lichen-forming fungi in the order Graphidales. The family contains nearly a hundred genera and more than 2000 species. Although the family has a cosmopolitan distribution, most Graphidaceae species occur in tropical regions, and typically grow on bark.
Graphidaceae was originally proposed by French botanist Barthélemy Charles Joseph Dumortier in 1822 (as "Graphineae"). Graphis, Opegrapha, and Arthonia were included in the new family.
In 2002, German lichenologist Bettina Staiger revised the Graphidaceae family in a monograph, proposing a new classification of genera that was widely accepted until molecular phylogenetic studies led to a further reorganization of the family.
Two subfamilies are recognized in the Graphidaceae:
Subfamily Redonographoideae, proposed by Lücking and colleagues in 2013, has since been promoted to familial status (as the monogeneric family Redonographaceae).
The family Thelotremataceae was placed in synonymy with Graphidaceae in 2008, after molecular phylogenetic analysis showed that the families formed several lineages within one strongly supported monophyletic lineage. This study also showed that many genera in Graphidaceae and Thelotremataceae were paraphyletic or polyphyletic. In 2018, Kraichak and colleagues, using a "temporal phylogenetic" approach to identify temporal bands for specific taxonomic ranks, proposed removing Fissurina from the Graphidaceae and instead as placing it as the type genus of Fissurinaceae, a family originally proposed by Brendan P. Hodkinson in 2012. They similarly suggested recognizing Diploschistaceae and Thelotremataceae as independent families. This taxonomic proposal was rejected by Robert Lücking in a critical 2019 review of the temporal method for the classification of lichen-forming fungi, using these specific examples to highlight several drawbacks of this approach. He noted "there is substantial loss of information content in this alternative classification at the second most important rank, the level of family, and such a revised classification is practically meaningless. It makes more sense to apply such essentially phylogenetic classifications, with less information content, to infraranks, such as subfamily or tribe".
The photosynthetic partner of Graphidaceae fungi is typically green algae from the genus Trentepohlia, or very rarely Trebouxia. The lichen thallus is typically crustose, which means it forms a crust-like structure on the it grows on. The form of the ascomata of Graphidaceae are usually (cup-shaped), (narrow, and slit-like) or (round or oval-shaped structure and embedded in the substrate), but can be rarely (with a powdery mass of ascospores and formed by the disintegration of the asci). They are usually (with both a and a), but are sometimes (without a thallus margin) or (surrounded by a pale thalline margin). The, which is the hyphae and tissue that between the asci, consists of usually unbranched, sometimes, rarely branched and anastomosing paraphyses. In some lineages, the paraphyses may be apically (covered with small spines or projections at the tips), and there may be lateral in some lineages. The asci are, which means they have a ring structure protruding into the and with an apical . They are non-amyloid or amyloid in some lineages, such as in the genus Diorygma. The asci are to oblong or in shape.
The ascospores of Graphidaceae number primarily 8 per ascus but can often be reduced to 2–4 or 1 per ascus. They are transversely septate to (elongated and divided into multiple compartments by transverse and longitudinal septa), usually ellipsoid to oblong, and often have forming and lens-shaped to rounded lumina. This particular set of features is known as "graphidoid". The spores can be hyaline (colourless) to (dark) brown, and the endospore is often amyloid. Graphidaceae also have pycnidia for producing conidia, which are non-septate, usually oblong, and hyaline.
The vast majority of Graphidaceae species are restricted to the tropics. Most Graphidaceae species are epiphytic (i.e. they grow only on plants). Forty-two species are known from the Galápagos Islands, where they are among the most diverse of the crustose lichens there. Mexico is thought to be a biodiversity hotspot of undiscovered Graphidaceae species, with about 430 species predicted to occur in tropical regions, compared to less than 200 recorded in the entire country.
According to the Catalogue of Life, there are 94 genera and more than 2100 species in Graphidaceae. In terms of number of species, Graphidaceae is the second-largest family of lichen-forming fungi, after the Parmeliaceae (2765 species) and ahead of the Verrucariaceae (943 species). The following list gives the genus name, its taxonomic authority, year of publication, and the number of species: