Malmidea subcinerea is a crustose lichen characterised by a continuous thallus that ranges from 80 to 120 μm in thickness. The thallus surface is smooth and dull, with colours from grey and greenish grey to olive, and neither isidia nor soralia present. The medulla of the thallus is white and does not react to a solution of potassium hydroxide (K−).[1]
This species' photobiont is chlorococcoid, consisting of green algal cells measuring 10–12 μm in diameter. The apothecia of Malmidea subcinerea are sessile and rounded, measuring between 0.4 and 0.9 mm in diameter and 0.2–0.3 mm in height. Initially, the apothecial discs are flat but become slightly convex, coloured light beige to light greyish brown. The margins around the discs are approximately 0.15 mm thick, slightly prominent, and vary from whitish grey to brownish grey in colour.[1]
The excipulum is of the piperis-type, more or less hyaline (translucent) at the periphery and brownish at the centre and upper periphery. This species lacks hydrophobic granules. The subhymenium is about 10 μm high, hyaline or slightly brownish, while the hypothecium is centrally 50–70 (up to 125) μm high, dark brown to reddish brown, and does not react to potassium hydroxide (K−). The epihymenium, if present, is light brown, and the hymenium is hyaline, measuring 100–120 μm in height.[1]
The asci within Malmidea subcinerea are 60–75 by 10–15 μm in size, each containing 6–8 ascospores. These spores are broadly ellipsoid to fusiform, lack septate (internal partitions), with a uniformly thickened wall and a halo approximately 1 μm thick. The spore sizes range from 9–12 by 5–7 μm.[1]
Chemically, no lichen substances were detected in Malmidea subcinerea through thin-layer chromatography analysis.[1]
