Heterodermia apicalis
Heterodermia apicalis is a corticolous lichen in the family Physciaceae. It was described from specimens collected on granite outcrops in primary rainforest at Reserva Cristalino in Mato Grosso, Brazil. The lichen is separated from similar Heterodermia species by the patchy yellow pigment and black-edged patches on parts of its lower surface.
Taxonomy
Heterodermia apicalis was described in 2022 by André Aptroot and Maria Fernanda de Souza Silva from material collected on granite outcrops in primary rain forest in the Reserva Cristalino, at elevation. The holotype, the single reference specimen for the name, is deposited in the herbarium of the Federal University of Mato Grosso do Sul. Within Heterodermia, it is placed in the H. dactyliza species group and was compared with H. flavodactyliza. Both have a similar foliose thallus, but H. flavodactyliza has web-like orange pigment over most of the lower surface, whereas H. apicalis has spotted to patchy yellow pigment and black margins only on parts of the lower surface. In the key to Brazilian Heterodermia species it falls in the couplet for taxa with spotted yellow pigment on the lower surface.
Description
The thallus of Heterodermia apicalis is foliose, ochraceous gray and loosely attached to the rock. It forms rosettes up to about wide and is roughly 150 μm thick. The upper is about 70 μm thick, and there is no distinct lower cortex. The branch unequally, 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, and isidia are absent. However, the tips of secondary lobes are often slightly upturned and white, suggesting incipient soralia. 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. 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 to irregular side branches. Apothecia have not been observed, but pycnidia 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+. Thin-layer chromatography detected atranorin and zeorin, along with a terpenoid and the anthraquinones emodin and 5,7-dichloroemodin as lichen substances.
Habitat and distribution
Heterodermia apicalis grows on granite in rock outcrops within primary rainforest in the Reserva Cristalino region of Mato Grosso, Brazil, at about elevation. At the time of its original publication, it was known only from Brazil. As of 2025, no additional records had been published.