Pyxine philippina

Pyxine philippina is a foliose lichen, meaning it has a leaf-like growth form. The thallus (the vegetative body of the lichen) is thin to moderately thick and lacks both soredia (powdery propagules) and isidia (coral-like outgrowths). The upper surface is whitish, fairly opaque, and epruinosus (without a pruinose or frosted covering), appearing smooth. The medulla (inner layer) is white. When tested with potassium hydroxide solution (the K test), the upper surface turns lutescent (yellowish), followed by rubescent (reddish). The lobes (divisions of the thallus) measure 0.5–1.4 mm in width and are irregular in shape, somewhat contiguous (nearly touching), and confluent (flowing together), often very confluent. They are flat or partially convex, appearing blackish beneath. The rhizines (root-like attachment structures) are short and blackish in colour.^[2]

The apothecia (disc-shaped fruiting bodies that produce spores) measure 1–4 mm in width and are lecideine in form (lacking a distinct thalline margin formed by thallus tissue). The margin is blackish or occasionally ashy-blackish in colour, fairly slender or of moderate thickness, whilst the disc is flat, black, and nude (bare in texture). The excipulum (outer rim of the apothecium) has an interior that is verdigris to sooty coloured and reacts strongly to potassium hydroxide, or occasionally appears whitish to ashy.^[2]

The hypothecium is distinctly brownish above and shows no reaction to potassium hydroxide, whilst appearing whitish below or occasionally becoming ashy. The spores, which number eight per ascus, are arranged in two rows, appearing brownish, oblong, and blunt to polarilocular (with polar thickenings separated by a thick septum containing a connecting channel). The spores are divided by a single cross-wall (1-septate) with membranes that are unequally thickened, particularly in the apices and at the septum, measuring 15–23 micrometres (μm) in length and 6–8 μm in width.^[2]

Pyxine philippina was originally described from specimens collected at two locations in the Philippines. The type material includes collections from Luzon (Subprovince Bontoc, Vanoverbergh 780) and from Subprovince Benguet (Merrill 7934), both growing on tree bark.^[2] Pyxine philippina is one of 14 Pyxine species that have been recorded from the Philippines,^[3] and one of nine in the genus that was first described from specimens collected in the country.^[4] The lichen has since been widely documented across Asia, including Bhutan,^[5] India,^[6] Japan,^[7] Nepal,^[8] and Thailand.^[9]