Malmidea isidiifera is a species of corticolous (bark-dwelling), crustose lichen in the family Malmideaceae. It is found in Brazil and Venezuela.
The lichen was formally described as a new species in 2021 by German lichenologist Klaus Kalb. The type specimen was collected from Itatiaia National Park (Rio de Janeiro) at an elevation of . The species epithet alludes to the presence of isidia on the thallus. The species also occurs in Venezuela.
Malmidea isidiifera is characterised by a crustose thallus that is continuous and has a thickness ranging from 30 to 70 üm. The thallus surface is smooth to slightly and dull, with a grey colour that turns orange-red when the cortex is abraded. The species is distinguished by its isidia, which are to , densely covering the thallus, each measuring 0.05âÂÂ0.1 mm in length and 0.05 mm in width. The medulla of the thallus is orange-red and has a K+ (purple) chemical spot test reaction.
The of Malmidea isidiifera is , with cells measuring 6âÂÂ8 üm in diameter. The apothecia are sessile and rounded, varying in diameter from 0.7 to 1.5 mm and in height from 0.4 to 0.5 mm. Initially, the of the apothecia are flat, but they become distinctly convex over time, with a colour range from light brown-grey to dark brown. The margin of the apothecia is thin, about 0.1 mm thick, slightly prominent, and varies in colour from whitish grey to dark brownish grey.
The of the species is of the piperis-type and is hyaline (translucent) at the periphery, with the inner part being reddish to dark brown. It lacks hydrophobic granules, which occur is some other species in genus Malmidea. The is about 20 üm high and ranges from hyaline to light brown. The is significantly larger, measuring 150âÂÂ200 üm in height, and is reddish to dark brown, showing no reaction to the K spot test. The of Malmidea isidiifera is indistinct, while the hymenium is hyaline and measures 100âÂÂ140 üm in height.
The asci are 70âÂÂ100 üm long and 20âÂÂ25 üm wide, each containing 6 to 8 broadly ellipsoid to ascospores. These ascospores lack septa (internal partitions), and have walls that are equally thickened and surrounded by a about 1 üm thick. The measure 17âÂÂ23 by 7âÂÂ10 üm.
In terms of chemistry, Malmidea isidiifera contains atranorin and norsolorinic acid, both major components in its makeup.