Biology:Septotrapelia

Septotrapelia is a genus of lichen-forming fungi in the family Pilocarpaceae. It comprises four species. Species in this genus form tiny, scale-like crusts on rocks and are distinguished by their chocolate-brown fruiting discs with pale margins and unusually large ascospores divided into three segments. These small, bluish-grey lichens grow primarily on volcanic boulders and weathered stone in tropical and subtropical regions, from Costa Rica and the Galápagos to Thailand and South Korea. The genus was established in 2007 after DNA studies showed that certain species with this distinctive spore structure did not fit into existing lichen groups.

Taxonomy

Septotrapelia was introduced in 2006 by André Aptroot and José Luis Chaves as part of a study describing several new squamulose lichen-forming fungal genera; unlike the ramalinaceous novelties in that paper, Septotrapelia was placed in the Pilocarpaceae. The type species, S. glauca, was described from specimens collected from volcanic boulders in pasture near Tenorio Volcano National Park, Guanacaste, Costa Rica (about 700 m elevation); the holotype is housed at the Instituto Nacional de Biodiversidad (INB).

Aptroot and Chaves separated the genus from superficially similar Trapelia and Trapeliopsis on combined [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]]: a dull bluish, squamulose thallus; [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] apothecia; and large, [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]], 3-septate ascospores. They noted that no existing pilocarpaceous genus combined a squamulose thallus with 3-septate spores, and that the spore size exceeded that known in the family—features that, together with the apothecial anatomy, supported recognition at generic rank. The authors also included a new combination for the widespread paleotropical crustose species Septotrapelia triseptata (Hepp) Aptroot, based on Lecidea triseptata (type: Java). The 2006 generic name, however, was not validly published under the prevalent nomenclatural rules: Index Fungorum records it as nom. inval., citing Art. 38.5(a), indicating that the protologue lacked a compliant description/[[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] or reference to one. The name was validated the following year by Aptroot and co-authors, who published the genus and type species in Fungal Diversity (2007), where they also treated the combination S. triseptata.

Description

Septotrapelia comprises small, bluish-grey, squamulose (scale-forming) lichens. The thallus is dull, [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] (with a fine powdering) and forms convex, elongate [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] about 0.2–0.4 mm wide and up to 2 mm long that may overlap into a [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] mat; thinner thalli are packed with algal cells, whereas thicker ones develop a white medulla beneath the [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]]. The upper [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is irregularly [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] and crystal-laden; no [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is developed.

Apothecia are [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] (with a pale, thallus-coloured margin), initially round then often lobed, 0.5–2.0 mm in diameter, with a dark chocolate-brown, dull [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] that may carry sparse white [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]]. The [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is prominent and can stand above the disc. The [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is sharply delimited, with an outer hyaline layer over a mottled dark-brown inner portion; the [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is similarly dark brown. The hymenium is non-inspersed, and the [[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]] is brown with tiny crystals. The supporting threads between spore sacs (paraphyses) have internal walls and fuse together where they meet. The spore sacs (asci) have a distinctive cap structure ([[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]]) characteristic of the family Pilocarpaceae that stains blue with iodine after alkali treatment (IKI+ after KOH). Spores are colourless, club-shaped ([[Glossary of lichen terms#{{biology:{1}}}|{{Biology:{1}}}]]), and divided by three cross-walls (3-septate), typically (23–)30–35 × (6–)8–10 μm in size, with a strong constriction at the middle wall and a thin jelly-like outer coating.

Pycnidia occur on the lobes as small, pinkish-yellow spherical structures (about 0.4 mm), producing rod-shaped conidia 5–6 × 1 μm. In standard spot tests the thallus is K−, C−, PD− and UV−; thin-layer chromatography shows usnic acid and a terpene, and the chemistry of the medulla is otherwise unremarkable.

Habitat and distribution

Septotrapelia is a saxicolous (rock-dwelling) genus: the type species (S. glauca) grows on volcanic boulders in open pasture near Volcán Tenorio National Park, Guanacaste, Costa Rica, at around 700 m elevation. Aptroot and co-authors also pointed to two further elements likely assignable to the genus: a sterile, sorediate, squamulose crust from the Galápagos (saxicolous), and a crustose species they recombined as S. triseptata, which is common and often abundant on soil and weathered rock, particularly in tropical Asia.

Species

• Septotrapelia glauca Aptroot & Chaves (2007) – Costa Rica
• Septotrapelia multiseptata Aptroot & K.H.Moon (2014) – South Korea
• Septotrapelia triseptata (Hepp) Aptroot (2007) – tropical Asia
• Septotrapelia usnica (Sipman) Kalb & Bungartz (2013) – Galápagos Islands

References

Wikidata ☰ {{{from}}} entry