Pannaria howeana

The thallus forms a loose, foliose rosette, typically 5–10 cm across, and is only weakly attached to the bark substrate. The lobes are irregularly branched and slightly concave, about 1.5–3.0 mm wide, with a distinctly narrow, recurved margin. Small, ascending lobules are also present. The upper surface is pale greenish grey when fresh and becomes pale yellowish brown in herbarium storage. It is glossy and mostly smooth, with only a faint tomentum near the margins. The lower surface lacks a true lower cortex. Instead, the lowest part of the medulla forms a pattern of pale brown, radiating hyphae. Rhizines are sparse, pale brown, and unbranched, mostly concentrated in the older central parts of the thallus.^[2]

Pannaria howeana is a tripartite lichen with two photosynthetic partners: a green alga in the main thallus and cyanobacteria housed in cephalodia. The cephalodia are common on the upper surface and contain Nostoc. Apothecia, the fruiting bodies, are common, with rufous-brown discs and a thalline margin that is crenulate-striate and strongly incurved. Each ascus contains eight spores. The ascospores are ellipsoid and roughened, measuring about 13.5–17.0 × 8–10 μm. Including the perispore, they measure 14–18 × 9–11 μm, and they lack apical extensions. Thin-layer chromatography detected porphyrilic acid and vicanicin as the main lichen substances, with leprolomin only weakly present or absent.^[2]

Pannaria howeana is a bark-dwelling lichen endemic to Lord Howe Island. It is known from the summit area of Mount Gower, where it was collected at 820 m. It grew on a shaded stem of Dracophyllum in low summit vegetation dominated by Metrosideros nervulosa, Zygogynum howeanum, Didymocheton pachyphyllus, Dracophyllum, tree ferns, and palms. No additional localities have been reported, and its population status on the island remains poorly documented.^[2]