Biatora aureolepra

Biatora aureolepra forms a thin, leprose crust that is bright yellow-green when fresh but often fades to straw-coloured or golden tones in older herbarium specimens. The thallus lacks any layered (stratified) structure; instead, the fungal filaments grow partly within the outer bark or sapwood (endosubstratal), while a single surface layer of powdery soredia builds a patchy film several centimetres across. Individual soredia are usually 18–21 μm in diameter (occasionally as small as 13 μm or as large as 30 μm) and frequently clump into consoredia up to 70 μm wide; viewed under polarised light these granules glitter with minute crystals. A slender, whitish prothallus may outline young colonies. The green-algal partner (a chlorococcoid photobiont) consists of jelly-sheathed cells 6.5–14 μm wide that tend to cluster together.^[2]

No sexual fruit-bodies (apothecia) or asexual pycnidia have yet been observed, so the species is known only from its vegetative crust. Chemical tests reveal 5-O-methylhiascic acid as the dominant secondary metabolite, accompanied by traces of gyrophoric and lecanoric acids; a quick rose-violet flash on the thallus with bleach (C+) is characteristic, while reactions with potassium hydroxide solution (K) and para-phenylenediamine (Pd) are negative.^[2]

In North America the lichen is confined to interior wet-belt forests of British Columbia and neighbouring Montana, where it colonises bark or decaying wood of western redcedar (Thuja plicata) and western hemlock (Tsuga heterophylla) within humid, old-growth stands that are mostly more than three centuries old. Sites range from about 525 to 930 m (1,722 to 3,051 ft) elevation and share a microclimate of persistent ground-level moisture beneath closed canopies.^[2]

Across the North Atlantic, records from central Norway and, further south, a recent collection from the Hallstatt area of the Austrian Alps place B. aureolepra on bark and dead wood of Norway spruce (Picea abies) in cool, rain-drenched spruce forests of late-successional age. The Austrian specimen, gathered along the Waldbach river at about 540 m (1,770 ft) altitude in a shaded gorge that receives more than 1,800 mm (71 in) of annual precipitation, formed a straw-coloured, sterile thallus up to 9 cm across.^[2][3]

These scattered localities—north-western North America, boreal Norway and the Central European Alps—reveal a markedly disjunct, moisture-dependent distribution that echoes patterns seen in several other inland-rainforest lichens. Given its minute, sterile habit and the limited number of targeted surveys, the species is probably under-recorded; nevertheless, its reliance on long-undisturbed, humid conifer stands means that continued logging and stand conversion in such forests could threaten its continuity.^[2][3]