Pannaria howeana

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Pannaria howeana

Pannaria howeana is a rare lichen in the family Pannariaceae. It forms loose, leaf-like rosettes on tree bark in the montane plant communities of Mount Gower, Lord Howe Island, New South Wales, Australia. The rosettes are up to about 10 cm across and are only weakly attached to the bark. It has a pale greenish-grey to pale yellowish-brown upper surface, a lower surface without a true cortex, and a distinctive pattern of pale brown, radiating hyphae on the medulla. This lichen is unique for its sparse rhizines and a chemical mix that includes porphyrilic acid.

Taxonomy
- Described as a new species in 2012 by the Norwegian lichenologist Arve Elvebakk, based on material from Lord Howe Island.
- The holotype was collected on February 11, 1995, from a shaded Dracophyllum stem on the Mt Gower summit at about 820 m.
- Pannaria howeana is part of a tripartite lichen system with a green alga in the main body and Nostoc cyanobacteria in cephalodia on the upper surface. It is related to Pannaria araneosa from New Zealand but differs in having thinner lobes, less surface hairiness (tomentum), and a distinct chemistry that includes porphyrilic acid and vicanicin, with little to no leprolomin.

Description
- Thallus: loose rosette, 5–10 cm across, only weakly attached to bark. Lobes are irregular and slightly concave, about 1.5–3 mm wide, with narrow, recurved margins. Small ascending lobules may be present.
- Surface: upper surface pale greenish grey when fresh; becomes pale yellowish brown in herbarium specimens; glossy and mostly smooth with only faint tomentum near the edges. Lower surface lacks a true cortex; the medulla shows pale brown, radiating hyphae. Rhizines are sparse, pale brown, and unbranched, mostly in the center.
- Reproduction: Apothecia are common, with rufous-brown discs and a crenulate (scalloped) thalline margin.
- Spores: each ascus has eight spores; ascospores are ellipsoid, about 13.5–17 × 8–10 μm; with perispore, 14–18 × 9–11 μm; they lack apical extensions.
- Chemistry: porphyrilic acid and vicanicin are the main lichen substances; leprolomin is weakly present or absent.

Habitat and distribution
- Endemic to Lord Howe Island and known only from the summit area of Mount Gower (about 820 m).
- It grows on shaded Dracophyllum stems in a montane vegetation community that includes Metrosideros nervulosa, Zygogynum howeanum, Didymocheton pachyphyllus, Dracophyllum, tree ferns, and palms.
- No additional localities have been reported, and the species’ overall population status on the island is not well documented.