Thallus effuse, wide-spreading, creamy-white to pale grey; 0.3–0.5 mm thick, cracked-areolate, areoles flat to uneven, 0.5–1.0 mm across; soredia and isidia absent. Primary photobiont green, in irregular colonies forming a discontinuous layer, cells globose, 8–10 µm diam. or oblong 15 × 10 µm; secondary photobiont frequent, often abundant, forming dark red-brown, linear to radiating-stellate groups, (0.2–)0.3–0.7(–1.4) mm across, individual colonies linear, 0.2–0.4 × 0.05–0.1 mm, immersed in the thallus surface; cells red (K+ purple) at thallus surface, pale blue (K+ very pale blue-green) within thallus, irregularly globose, 12–15(–20) µm diam., mostly singular but occasionally two cells enclosed in a sheath (?Gloeocapsa).
Apothecia occasional, scattered, 1–3 (or more) immersed in scarcely raised thalline warts, (0.8–)1.0–1.2(–1.4) mm diam., with pruinose surface; individual apothecia (0.25–)0.3(–0.4) to 0.5 when singular. Hymenium 300–350 µm, I–; paraphyses slender (1–1.5 µm) mostly unbranched, but branched and anastomosing above and terminating in a conglutinate yellowish-brown granular epihymenium; hypothecium hyaline, composed of loosely arranged branched and anastomosing hyphae. Asci Pertusaria-type, 200–250 × 60×80 µm, ascospores 1/ascus, (127)157.5 – 193.5 – 229.3(247) × (36)49.0 – 70.0 – 91.0(105) µm.
Conidiomata not observed.
Chemistry: K–, C–, Pd+ orange-red; protocetraric acid (major), fumarprotocetraric acid (trace), confumarprotocetraric acid (trace) & virensic acid (trace) by HPLC
Several collections from the Auckland Islands, Campbell Island and Isla Desolacion (Chile). This disjunct distribution (NZ Shelf Islands/Isla Desolacion) is shared by several other saxicolous species.
This species is unique in Pertusaria in that it has cephalodia, which are otherwise unknown in the genus. The thallus is covered with immersed, dark red, stellate cephalodia composed of red (K+ purple), unicellular cells. Pertusaria stellata is chemically identical to the South American P. macloviana but that species has shorter ascospores (mean: 164.1 x 70.8 µm).
Imshaug was calling this taxon P. obvelata Nyl., a name that has now been lectotypified on a different species of Pertusaria and shown to be a saxicolous form of P. velata (Fryday & Coppins 2006).
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