Malmidea rhodopisoides is a crustose lichen with a thallus thickness of 20–40 μm. It is composed of isidia-like granules forming clumps that densely cover an orange-red prothallus. The thallus surface is dull, showing shades of grey to greenish grey, which turns orange-red when the cortex is abraded. Its medulla is also orange-red and has a K+ (red) chemical spot test reaction.[1]
The species' photobiont is chlorococcoid, with cells measuring 6–8 μm in diameter. Apothecia are sessile and rounded, measuring 0.7–1.5 mm in diameter and 0.4–0.5 mm in height. The apothecial disc is initially flat but becomes slightly convex, ranging in colour from beige to dark brown. The margin around the disc is about 0.1 mm thick, bulging, and elevated above the disc, typically orange-red and occasionally partly blackish.[1]
The excipulum of Malmidea rhodopisoides is of the piperis-type, hyaline (translucent) at the periphery, with the inner part containing hydrophobic granules of norsolorinic acid. The subhymenium is approximately 20 μm high and varies from hyaline to light brown. The hypothecium is relatively tall, ranging from 200 to 400 μm, reddish to dark brown in colour, and does not react to potassium hydroxide (K−). The epihymenium of the species is either indistinct or slightly granular, while the hymenium is hyaline and stands 70–80 μm high.[1]
Asci within this species measure 60–70 by 20–25 μm, each containing 6–8 ascospores. These spores are broadly ellipsoid to fusiform, lack septa (internal partitions), with a uniformly thickened wall and a halo approximately 1 μm thick. The size of the spores ranges between 15 and 20 by 9–12 μm.[1]
Chemically, Malmidea rhodopisoides is characterized by a major presence of norsolorinic acid and a lack of atranorin.[1]
