Pseudopeltula myriocarpa

Pseudopeltula myriocarpa is a species of rock-dwelling squamulose lichen in the family Lichinaceae. It forms small, olive-colored, shield-shaped scales on limestone and dolomite. The species is the type of its genus and is distinguished by its fruiting bodies, which become aggregated into dark, spot-like stromatic patches up to about 2 mm across. It occurs in Mexico and the Caribbean.

Pseudopeltula myriocarpa was described as a new species in 1995 by the lichenologist Aino Henssen. In that paper, Henssen designated P. myriocarpa as the type species of Pseudopeltula, a genus of small, olive cyanolichens with an ecorticate thallus (lacking a true cortex) and unusually complex, mature apothecia.^[1]

The species epithet myriocarpa refers to the many small apothecia that ultimately become packed together in a partly stromatic tissue. In Henssen's key to Gloeoheppiaceae, P. myriocarpa is identified by its fruiting bodies being aggregated into stromata that appear as circular to rosette-shaped spots up to about 2 mm across. Henssen also emphasized that, unlike Pseudopeltula heppioides (where the hymenium subdivides into small excipulate units), P. myriocarpa develops true stromatic fruiting bodies.^[1]

A 2024 phylogenetic reclassification of the Lichinomycetes did not support recognizing a separate family for Gloeoheppia (Gloeoheppiaceae), and instead treated the genus within Lichinaceae.^[2]

The thallus is olive-colored and made up of squamulose to peltate units, with margins that curve downward and a lower surface that is tomentose. Individual squamules may be single or clustered, often convex to somewhat spherical, and can reach about 7 mm in length. They attach to the substrate by rhizoidal strands that may merge into an umbilicus. In cross-section, the thallus is typically about 380–480 μm thick and includes a well-developed tomentum layer.^[1]

Fruiting bodies are produced in dark brown to blackish stromata that form spot-like patches (often more or less rosette-shaped) up to about 2 mm wide. The spore-bearing layer (the hymenium) is about 110–115 μm tall and becomes subdivided by sterile hyphal strands. In iodine it stains deep blue and then turns brown-red, while the subhymenium stains bluish. The cylindrical asci usually contain 6–8 spores (about 75–95 × 11–11.5 μm), and the ascospores are mainly simple, ellipsoid, and colorless, although two-celled spores were occasionally observed. Pycnidia are immersed and can be large, producing small rod-shaped conidia. Henssen described the development of the stromata as a cumulative process: small apothecia form densely, the hymenium becomes partitioned, and additional apothecia arise within or beneath older tissue, producing a single, horizontally spreading stromatic patch with uneven ridges or wart-like projections.^[1]

Pseudopeltula myriocarpa is a calcicolous lichen that grows on carbonate rocks, reported from dolomite and limestone. The type specimen was collected in Mexico (Querétaro, near Jalpan de Serra) on dolomite on a dry slope, and the paratype was collected in Guerrero (18 km SSE of Taxco) on a limestone cliff at about 1,360 m elevation. In Henssen's 1995 treatment, the species was known from only these two Mexican localities.^[1] It has since been recorded from the Guánica State Forest in Puerto Rico,^[3] and the Isla de la Juventud in Cuba.^[4]