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Fungi make up the second largest kingdom, with an estimated number between one and ten million species. They include an enormous variety of life styles, ranging from microscopic yeasts, to saprotrophs decomposing organic matter, to parasites of plants, animals, and even fungi, to mutualistic symbioses including endo- and ectomycorrhiza and lichens. Lichenization plays an important role in fungal evolution, particularly in the Ascomycota, where lichens make up thirty percent of the currently recognized species or a total of nearly 18000 taxa.

Graphidaceae is the largest family of tropical crustose lichens and probably the largest family of all lichenized fungi, with 2300 currently recognized and a predicted total of over 4000 species. The family is the most important element of lichen communities in tropical rain forests. Graphidaceae includes several groups that historically were considered separate families: Thelotremataceae, Gomphillaceae, Asterothyriaceae, and Solorinellaceae. The revised classification currently accepted distinguishes four subfamilies: Gomphilloideae, Fissurinoideae, Redonographoideae, and Graphidoideae. The latter three are considered the 'core' Graphidaceae, as they correspond to the previously recognized families Graphidaceae and Thelotremataceae, which comprise mostly epiphytic lichens with trentepohlioid photobiont and graphidoid, distoseptate ascospores. In contrast, subfamily Gomphilloideae includes many species growing on soil, bryophytes, and especially leaves, with chlorococcoid photobiont and thin-walled, euseptate ascospores. Transitions between these groups do exist, however. The largest subfamily, Graphidoideae, contains seven tribes: Acanthothecieae, Diploschisteae, Graphideae, Leptotremateae, Ocellularieae, Thelotremateae, and Wirthiotremateae. Until recently, only 13 genera were distinguished in the core Graphidaceae, but this number has grown within a decade to over 70 genera, with more than 20 additional genera in subfamily Gomphilloideae.

Tropical epiphytic Graphidaceae often grow endoperidermal in the upper, dead layers of tree bark. In some species, the thallus forms a hollow cavity below that is inhabited by ants or termites. The family is most diverse in lowland rain and lower montane forests between sea level and 2000 meters, with some groups extending into dry forests and upper montane regions. Many genera are indicators of the conservation status of tropical ecosystems, being most diverse in, or restricted to, oldgrowth primary forest. Graphidaceae is very rich in secondary chemical substances, with potential interest for pharmaceutical screening programs.

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