Pyxine is a genus of foliose lichens in the family Caliciaceae. The genus has a widespread distribution in tropical regions. It was established in 1825 by the Swedish botanist Elias Fries and is distinguished from similar lichens by its characteristic golden fluorescence under ultraviolet light due to the compound lichexanthone. These small, leaf-like lichens form radiating rosettes with narrow and tiny white lines called pseudocyphellae that act as air vents on their upper surface.
Taxonomy
The Swedish botanist Elias Magnus Fries erected the genus Pyxine in 1825, selecting Lecidea sorediata (now Pyxine sorediata) as the type species and placing it in his tribe Pyxinae alongside Umbilicaria because both possessed a "naked" . By 1885 William Nylander already recognised four species whose circumscription is broadly retained today. Fertile Pyxine is distinguished from kindred foliose genera such as Physcia, Dirinaria and Physconia by a subtle purple-violet reaction of the apothecial epithecium to potassium hydroxide solution, a characteristically dark and, most conspicuously, apothecial margins that usually lack algal cells. Additional hallmarks—including frequent pseudocyphellae and a lichexanthone-rich cortex that fluoresces golden under long-wavelength ultraviolet light—were noted early in its study and remain reliable diagnostic features.
Dirinaria is generally accepted as Pyxines closest ally; both genera grow in tropical and subtropical regions and were even combined by some nineteenth-century authors. Nevertheless, they differ consistently in thallus architecture—Dirinaria lobes tend to coalesce laterally, a condition absent in Pyxine—and in secondary chemistry, with Pyxine commonly pairing triterpenes with norstictic acid rather than the divaricatic acid-series compounds typical of Dirinaria.
Description
Pyxine lichens form small, leaf-like (foliose) rosettes whose lobes radiate from a more-or-less central point. Individual lobes are typically narrow—often no more than 0.3–1.5 mm wide—and may look slightly wavy or even swollen in some species. The upper surface is usually pearl-grey to dull yellow-grey and can develop a subtle sugary bloom () near the tips. A distinctive feature of the genus is the presence of pseudocyphellae: tiny breaks in the upper that appear as fine white lines or a faint network; these act as microscopic air-vents and are absent from many look-alike genera. Vegetative propagules occur along a continuum: some species have fluffy soredia, others pustule-like cushions, and a few produce true cylinder-shaped isidia, so a specimen may show more than one kind of outgrowth on the same thallus. The underside is black with sturdy black root-like rhizines that keep the thallus firmly attached to bark or rock.
The fruiting bodies (apothecia) sit flush with the thallus and carry a flat to slightly domed blackish surrounded by a low rim that often lacks algae, giving an almost look. Slice tests show the rim is in fact a modified margin, and a pale internal stalk tissue ("stipe") may be visible beneath the disc; when a drop of potassium hydroxide solution is added in section the epithecium typically turns a faint violet, another quick clue to the genus. Ascospores are thick-walled, brown, and two-celled. Chemically, most Pyxine species manufacture the yellow pigment lichexanthone in the upper cortex—specimens glow gold under long-wave UV light—while the medulla often contains mixtures of norstictic acid, testacein, and characteristic triterpenes. This chemical palette, together with the dark hypothecium and reticulate pseudocyphellae, separates Pyxine from superficially similar members of the Caliciaceae such as Dirinaria and Physcia.
Species , Species Fungorum (in the Catalogue of Life) accept 47 species of Pyxine.
Pyxine albovirens Pyxine astipitata – Brazil Pyxine astridiana – neotropical Pyxine australiensis – Asia; Australia Pyxine berteriana – pantropical Pyxine boonpragobiana – Thailand Pyxine caesiopruinosa Pyxine coccifera Pyxine cocoes Pyxine cognata – pantropical Pyxine consocians Pyxine convexior Pyxine copelandii Pyxine cylindrica – Papua New Guinea Pyxine dactyloschmidtii Pyxine daedalea – Costa Rica Pyxine desudans – Australia Pyxine elixii – Australia Pyxine endochrysina Pyxine endocrocea Pyxine eschweileri Pyxine exoalbida – Brazil Pyxine fallax Pyxine farinosa – Papua New Guinea Pyxine flavicans – China Pyxine glaucescens Pyxine glaucovirescens Pyxine hengduanensis – China Pyxine jolyana – Brazil Pyxine katendei – Africa Pyxine keralensis – India Pyxine lilacina – Africa Pyxine lyei – Africa Pyxine mantiqueirensis – Brazil Pyxine mexicana Pyxine minuta Pyxine nana – neotropical Pyxine nubila Pyxine petricola – pantropical Pyxine plumea – Australia Pyxine profallax Pyxine pseudokeralensis Pyxine papuana – Papua New Guinea Pyxine philippina – Asia Pyxine punensis – India Pyxine pungens Pyxine pustulata – Brazil Pyxine pyxinoides – neotropical Pyxine retirugella Pyxine rugulosa Pyxine schmidtii Pyxine simulans – pantropical Pyxine sorediata Pyxine subcinerea – pantropical Pyxine subcoralligera Pyxine yercaudensis – India Pyxine yunnanensis – China
References