The Trypetheliaceae are a family of mainly lichen-forming fungi in the order Trypetheliales. The family consists almost exclusively of corticolous (bark-dwelling), crustose lichens with an almost strictly tropical distribution.
Trypetheliaceae was circumscribed by German botanist Franz Gerhard Eschweiler in 1824. His of the family was as follows (translated from Latin):"Thallus is crust-like. Apothecia are of varied shape, immersed in warts formed from the thallus's medullary substance." Eschweiler further notes that the family is almost exclusively found within the tropics. In his initial circumscription, he included the following genera: Arthonia, Porothelium, Medusula, Ophthalmidium, Trypethelium, Astrothelium, Glyphis, Chiodecton, and Conioloma.
The family Arthopyreniaceae was placed into synonymy with Trypetheliaceae, and its type genus, Arthopyrenia, was transferred to Trypetheliaceae in 2021. Other synonyms of Trypetheliaceae include Astrotheliaceae, Cryptotheliaceae, Hyalophragmiaceae, and Laureraceae. The order Trypetheliales was proposed in 2008 to contain the family.
In their 2016 revisionary synopsis of the Trypetheliaceae, André Aptroot and Robert Lücking accepted 418 species, distributed amongst 15 genera.
The general features of the Trypetheliaceae include a thallus that is mostly crustose, though the growth form of some species are to or even . The family displays a diverse array of appearances, ranging from clearly visible and to, hidden under bark, or even barely discernible from the . The growth habit and development of the thallus surface are influenced by a combination of environmental conditions and evolutionary factors.
The internal anatomy of the ascomata, including the, in this family is still an emerging area of research with potential taxonomic and systematic implications. One noteworthy aspect is that the ascomata in Trypetheliaceae can develop either superficially or emerge from beneath the periderm, with some species even exhibiting both forms. This divergence is seen in species such as Architrypethelium grande, Astrothelium megaspermum, and others. The wall of the ascoma is typically multi-layered and may contain a medullary layer. In some species, like Astrothelium megaspermum, an additional brownish 'medullary' layer is present. The intricate anatomy of the ascoma provides an array of that are used in the development of genus and species concepts within Trypetheliaceae.
Another consistent feature in most Trypetheliaceae is the, comprising thin, branching that form a network within a gelatinous matrix. However, the density and presence of the gelatinous matrix can vary across lineages. One feature, the hymenial inspersion, consists of oil droplets or infusions lining the paraphyses. The inspersion can be localized or spread throughout the hamathecium, and its taxonomic importance is still being uncovered.
The asci of Trypetheliaceae are typically, a structure best observed in species with larger . Additionally, ascospore type is a significant character in this family. While septation has historically been a key differentiator, recent understandings emphasize the nature of the septa and walls as more critical taxonomic indicators. The ascospores themselves can vary considerably, from the typical type to those that are multiseptate or, and this variation offers important insights into the relationships within the family.
The Trypetheliaceae family's chemical profile is less intricate than some tropical crustose families like Graphidaceae. The family's secondary substances primarily encompass xanthones and pigments, predominantly anthraquinones.
Lichexanthone is the most abundant xanthone, fluorescing a yellow hue under UV light, primarily on parts like the ascomata and thallus. Its presence, once a point of contention in taxonomy, is now considered species-specific due to phylogenetic studies. Another notable xanthone, coronatone, is less prevalent, showing an UV+ (orange) reaction.
Anthraquinones predominantly dominate the pigments in the Trypetheliaceae, manifesting in various parts of the lichen. Among these, parietin (also known as physcione) stands out as a yellow-orange substance. It is especially prevalent in species such as Astrothelium aeneum and Marcelaria cumingii, and has a purple reaction when tested with a K chemical spot test. Similarly, teloschistin, another yellow pigment present in Marcelaria benguelensis, also reveals a purple reaction to K. Xanthorin, on the other hand, offers a vibrant red hue and can be identified in Marcelaria purpurina, reacting purple with K+. While these are the more commonly noted pigments, there are several others like skyrin and emodin that appear in lesser quantities. The taxonomic significance of these lesser-found pigments, however, remains a subject of ongoing research.
Trypetheliaceae species, primarily found in tropical regions, are predominantly epiphytic, meaning these lichens mainly grow on other plants without deriving nutrients from them. Although largely confined to the tropics, there are a few exceptions, such as Viridothelium virens, which is found in temperate areas and occasionally on other than bark. This distribution and ecological pattern closely resemble that of the family Graphidaceae, but with notable differences: Graphidaceae species are more prevalent in extra-tropical regions and on a variety of substrates.
The Trypetheliaceae are often observed in semi-exposed or fully sun-exposed environments, such as forest canopies, open savannahs, and dry forests. In these settings, they frequently contribute to exatensive crustose lichen communities, distinguished by their production of yellow to orange pigments. Species with green thalli and partly or covered ascomata are more commonly found in the understory of rainforests. It has suggested that many undiscovered species may reside in these less studied, exposed canopy microhabitats.