Malmidea albomarginata

Malmidea albomarginata is a species of corticolous (bark-dwelling), crustose lichen in the family Malmideaceae. It is found in Venezuela.

Taxonomy

The lichen was formally described as a new species in 2021 by the lichenologists Klaus Kalb and Jesús Maldonado. The type specimen was collected by the authors from the Cerro El Volcán (Miranda) at an elevation of ; there it was found growing in a disturbed tropical mountain rainforest. The species epithet albomarginata alludes to the distinctive white margins that characterise its apothecia.

Description

Malmidea albomarginata is a crustose lichen with a continuous thallus measuring 200–300 ÃŽÂ¼m in thickness. The thallus surface is initially , with being scarce and unevenly distributed, each measuring 0.1–0.3 mm in height and 0.15–0.3 mm in width. Over time, the thallus becomes dull and transforms from grey or greenish-grey to a coralloid texture as it ages. This species lacks soralia and isidia. The medulla of both the verrucae and thallus is white to faintly yellow, reacting K+ (orange to reddish) when tested with potassium hydroxide, but without a reaction to the P spot test. The is , with cells around 6–8 ÃŽÂ¼m in diameter.

Apothecia in Malmidea albomarginata are sessile and rounded, ranging from 0.8–1.8 mm in diameter and 0.2–0.3 mm in height. The apothecial are flat to slightly convex, with colours varying from ochre to light greyish-brown. The is of the granifera type, , thin, and white. The is hyaline, while the medullary excipulum is whitish to slightly yellowish, filled with opaque, greyish to yellowish that partially dissolve in KOH, producing a K+ (orange-red) efflux. The is about 25 ÃŽÂ¼m high and hyaline to light brown, while the centrally located is 100–150 ÃŽÂ¼m high, narrowing towards the margin and dark brown, showing no reaction to K tests. The is indistinct, and the hymenium measures 75–90 ÃŽÂ¼m in height, being hyaline. Asci are sized 65–80 ÃŽÂ¼m by 12–18 ÃŽÂ¼m, containing 6–8 non-septate, , ellipsoid ascospores per ascus, measuring (10–)14 by 6–9 ÃŽÂ¼m, with a of 1.5–2 ÃŽÂ¼m.

Chemically, Malmidea albomarginata primarily contains atranorin, alongside several unidentified xantholepinones. It is distinguished from similar species like Malmidea attenboroughii by differences in apothecia size and the presence of atranorin. In comparison with Malmidea aurigera and Malmidea piperina, Malmidea albomarginata features larger apothecia, a paler apothecial disc, and warts that become coralloid granular.

References