Heterodermia apicalis

The thallus of Heterodermia apicalis is foliose (leaf-like), ochraceous gray and loosely attached to the rock. It forms rosettes up to about 9 cm (3.5 in) wide and is roughly 150 μm thick. The upper cortex is about 70 μm thick, and there is no distinct lower cortex. The lobes branch unequally (anisotomic branching), leaving large gaps between them. They are mostly flat, sometimes overlapping sideways, and measure 1.5–2.5 mm long by 0.6–1.2 mm wide. Soredia, phyllidia and isidia are absent. However, the tips of secondary lobes are often slightly upturned and white, suggesting incipient soralia (developing patches where soredia can form). The medulla is white. The lower surface lacks a cortex and bears scattered spots of yellow pigment. Toward the tips of some lobes, the pigment forms larger patches bordered by black margins about 0.2 mm wide. Cilia (hair-like outgrowths) are black and project from the lobe margins. They measure 0.5–1.7 mm long by 0.1–0.2 mm thick and are densely branched, with squarrose (spreading) to irregular side branches. Apothecia (sexual fruiting bodies) have not been observed, but pycnidia (asexual fruiting bodies) are present, though sparse and brown. In standard spot tests, the thallus shows no reaction in UV, C, K, KC, or P tests, but the yellow pigment is K+ (turning blood-red). Thin-layer chromatography detected atranorin and zeorin, along with a terpenoid (probably 6α,16β-diacetoxyhopane-22-ol) and the anthraquinones emodin and 5,7-dichloroemodin as lichen substances.^[2]

Heterodermia apicalis grows on granite in rock outcrops within primary rainforest in the Reserva Cristalino region of Mato Grosso, Brazil, at about 250 and 350 m (820 and 1,150 ft) elevation. At the time of its original publication (2022), it was known only from Brazil.^[2] As of 2025, no additional records had been published.^[3]