Arthothelium Diffluens

''Arthothelium'' is a genus of lichen-forming fungi in the family Arthoniaceae.

Description

''Arthothelium'' is a genus of crustose lichens, which can either be (embedded within the ) or superficial (growing on the surface). The thallus may spread freely or be confined to specific areas. The lichen's (the algae or cyanobacteria involved in its symbiosis) can vary, including types from the genus ''Trentepohlia (alga), Trentpohlia'', the family Chlorococcaceae, or may be absent altogether.

The reproductive structures resemble apothecia, a common form of lichen fruiting body, and come in various shapes, from flat to convex, and may be elongated or star-like. These structures, known as the , range in colour from red-brown to black, and can sometimes have a frosted, powdery appearance (). A , which in some lichens surrounds the fruiting body, is absent in ''Arthothelium''. The , a rim of tissue found in some lichen fruiting bodies, is also absent.

The uppermost layer of the apothecium, the , can be colourless, red-brown, or dark brown. Below this, the hymenium, where the spores develop, often turns blue when tested with iodine (I+). The , the supportive tissue beneath the hymenium, is variable in thickness and ranges from dark red-brown to dark brown in colour. The hymenium contains filaments called , which are sparsely to densely branched and often have swollen, red-brown tips.

The ascus, asci (spore-producing cells) are usually (club-shaped) or ellipsoidal, containing eight spores. They are semi-, meaning they have two wall layers that split during spore release, and feature a large apical dome with a distinct ocular chamber. The ascospores are to ellipsoidal, colourless, and , meaning they are divided by multiple internal walls, creating a brick-like pattern. This is a key distinguishing feature from similar genera like ''Arthonia'', where the spores are only divided by transverse walls.

Conidiomata (structures producing asexual spores) resemble those found in ''Arthonia''. The genus generally lacks lichen products (secondary metabolites), in species found in Britain and Ireland, but elsewhere, species may contain xanthones or anthraquinones.

''Arthothelium'' typically grows on smooth bark in humid, undisturbed habitats, although it is rarely found on rock. The genus includes around 50 species and has a cosmopolitan distribution, with most species occurring in tropical regions. It is considered polyphyletic, meaning the genus likely includes species that do not share a common evolutionary ancestor, and further study is needed on its type species, ''Arthothelium tremellosum''.

Species

, Species Fungorum (in the Catalogue of Life) accept 26 species of ''Arthothelium'':


* ''Arthothelium ampliatum''
* ''Arthothelium atrorubrum''
* ''Arthothelium aurantiacopruinosum''
* ''Arthothelium bacidinum''
* ''Arthothelium cinereoargenteum''
* ''Arthothelium desertorum''
* ''Arthothelium dictyosporum''
* ''Arthothelium diffluens''
* ''Arthothelium evanescens''
* ''Arthothelium feuereri''
* ''Arthothelium frischianum''
* ''Arthothelium huegelii''
* ''Arthothelium hymeniicola''
* ''Arthothelium infuscatum''
* ''Arthothelium insolitum''
* ''Arthothelium interveniens''
* ''Arthothelium isidiatum''
* ''Arthothelium japonicum''
* ''Arthothelium lirellans''
* ''Arthothelium macounii''
* ''Arthothelium macounioides''
* ''Arthothelium macrothecum''
* ''Arthothelium magenteum''
* ''Arthothelium microsporum''
* ''Arthothelium miesii''
* ''Arthothelium norvegicum''
* ''Arthothelium orbilliferum''
* ''Arthothelium polycarpum''
* ''Arthothelium pulverulentum''
* ''Arthothelium punctatum''
* ''Arthothelium ruanum''
* ''Arthothelium scandinavicum''
* ''Arthothelium spectabile''
* ''Arthothelium subspectabile''
* ''Arthothelium velatius''

References

{{Taxonbar, from=Q4797629

Arthoniaceae
Arthoniomycetes genera
Lichen genera
Taxa described in 1852
Taxa named by Abramo Bartolommeo Massalongo