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.
Taxonomy
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, the German lichenologist Bettina Staiger revised the Graphidaceae 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:
-
Fissurinoideae
-
Graphidoideae
Subfamily Redonographoideae, proposed by Lücking and colleagues in 2013,
Synonymy
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
paraphyly or
polyphyly.
In 2018,
Kraichak and colleagues, using a "temporal phylogenetic" approach to identify temporal bands for specific
, 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".
Description
The photosynthetic partner () of Graphidaceae fungi is typically
green algae from the genus
Trentepohlia, or very rarely
Trebouxia. The lichen
thallus is typically
crustose lichen, 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
ascus, 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 are most often produced eight per ascus, but in some lineages the number is frequently reduced to four, two, or even one. They range from simply transversely septum to (divided into many compartments by both transverse and longitudinal septa), and are typically ellipsoid to oblong. In many species the spore wall is built as an inner separated by , giving lens-shaped to rounded lumina; this combination of features is often referred to as "graphidoid". Spores may remain hyaline or become brown with age, and the endospore commonly reacts as amyloid. Graphidaceae also form pycnidia that produce conidia; these asexual spores are usually hyaline, non-septate, and oblong.
Some graphidaceous species have exceptionally large ascospores. In Ocellularia, the spores of O. subpraestans have been reported to reach about 880 × 65 in size, and can protrude through the apothecial pore and begin germination almost immediately, with produced from multiple cells of the muriform spore. Observations like these have been used to argue that very large, many-celled spores may favour establishment (and survival) even when dispersal is imperfect, including scenarios where spores are damaged or partly consumed during transport, potentially by invertebrates.
Distribution and ecology
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.
Diversification
Analyses of time-calibrated phylogenies indicate that Graphidaceae has diversified steadily over deep time. The family is estimated to have originated about 176 million years ago (Ma), with comparatively low, fairly uniform
speciation rates (about 0.06–0.10 lineages per million years) and brief accelerations early in its history and again around about 110 and 65 Ma. Two hyper-diverse
—
Graphideae and
Ocellularia sensu stricto—show the highest rates, and the most frequently inferred models include rate shifts near the stems of one or both of these groups. Cohort analyses recover pronounced heterogeneity across the family, resolving five broad diversification regimes rather than a single family-wide pattern. No clear correlation is evident between Graphidaceae speciation rates and long-term global temperature trends over the past ~180 million years.
The observed pattern is consistent with lineage-specific and ecological drivers. Graphidaceae is largely tropical, and major clades tend to occupy different —for example, Ocellularia s.str. is characteristic of shaded, protected tropical forest, whereas many Graphideae occur in more exposed sites—suggesting diversification linked to habitat differences rather than uniform climatic forcing. Pulses of diversification coincide with major events in plant and Earth history: Graphideae began diversifying soon after the origin of (c. 140 Ma), and Ocellularia s.str. diversified around the Cretaceous–Paleogene boundary (c. 65 Ma), contemporaneous with the expansion of angiosperm-dominated tropical rainforests; a perithecial in Ocellularia is also associated with higher diversification in trait-dependent analyses, consistent with a possible key innovation (pp. 5–6). Because species discovery is incomplete (recent estimates suggest the true species count may exceed 4,000) future taxonomic sampling may refine rate estimates and their timing.
Genera
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:
The genus Medusulina, proposed by Johannes Müller Argoviensis in 1894,
