Genus of lichens
Glaucotrema is a genus of lichen-forming fungi in the family Graphidaceae. It has five species.
Taxonomy.
The genus was circumscribed in 2012 by the lichenologists Eimy Rivas Plata and Helge Thorsten Lumbsch, with "Glaucotrema glaucophaenum" assigned as the type species. This lichen was originally described as a species of "Thelotrema" by August von Krempelhuber in 1875, and was later classified in the genus "Myriotrema". The genus name merges the suffix -"trema" with a portion of the epithet from its type species, "glaucophaenum".
Originally, "Glaucotrema" was proposed to contain the type and one other species, "G. costaricense". Three additional newly described species were added to the genus in 2014–2016, from collections made in Brazil and Thailand.
Description.
The thallus of "Glaucotrema" is characterised by a pale green-grey to pale olive-green colour, with a surface that can range from smooth to slightly uneven. It features a densely packed outer layer ( ;dfn id="" ;cortex ;/dfn ;) composed of tightly interwoven fungal cells ( ;dfn id="" ;prosoplectenchymatous ;/dfn ; structure). Within this structure lies a ;dfn id="" ;layer of algae cells ;/dfn ; (the ;dfn id="" ;photobiont ;/dfn ;), interspersed with clusters of calcium oxalate crystals.
The reproductive structures of "Glaucotrema", known as apothecia, are typically rounded to angular and can be either slightly emerging from the thallus or prominently displayed. The ;dfn id="" ;discs ;/dfn ; of these structures range in colour from flesh-colured to pale brown and are thinly covered with a white, powdery coating ( ;dfn id="" ;pruinose ;/dfn ;). The edges of these discs are usually smooth, though they can occasionally be fissured. While a true central support column ( ;dfn id="" ;columella ;/dfn ;) is absent, a pseudo-column ( ;dfn id="" ;pseudocolumella ;/dfn ;) often appears, consisting of tissue strands that originate from the side of the cup-like structure (lateral ;dfn id="" ;excipulum ;/dfn ;). The excipulum (the tissue surrounding the reproductive disc) also has a tightly interwoven cellular structure ( ;dfn id="" ;prosoplectenchymatous ;/dfn ;) and is typically colourless. It may either remain attached or become partially detached and perforated ( ;dfn id="" ;fenestrate ;/dfn ;). There are no hair-like structures ( ;dfn id="" ;periphysoids ;/dfn ;) around the edges of the disc. The spore-producing filaments (paraphyses) within the apothecia are simple and unbranched.
Spores produced by "Glaucotrema" are typically eight per sac (ascus), ellipsoid in shape, and divided into four parts by three cross-walls (3-septate), with thick dividers and lens-shaped internal spaces ( ;dfn id="" ;lumina ;/dfn ;). These spores are colourless and turn violet-blue when stained with iodine (I+ violet-blue). "Glaucotrema thailandicum" is unique in the genus in having ;dfn id="" ;submuriform ;/dfn ; ascospores. Chemically, "Glaucotrema" contains psoromic acid, which reacts yellow when tested with paraphenylenediamine (P+ yellow), indicating its presence.
References.
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