Lepraria eburnea

Lepraria eburnea forms a leprose thallus that is powdery to cottony in texture. The margin is typically diffuse (lacking clear boundaries), and lobes are usually absent. The medulla is usually present and thick, appearing white. The hypothallus is usually not distinct or visible. The thallus surface sometimes lacks soredia in patches, with these soredia often embedded in a hyphal weft. The soredia are abundant and mostly fine, measuring up to 60 micrometres (μm) in diameter, with projecting hyphae usually present ranging from short to long (up to 100 μm). Consoredia (aggregations of soredia) are present and can measure up to 200–400 μm. The species is characterised chemically by containing alectorialic acid, with three main chemical variants: one with alectorialic and protocetraric acids, another with alectorialic and psoromic acids (with 2'-O-demethylpsoromic acid in trace amounts), and a third containing only alectorialic acid. Chemical spot tests show K− or K+ (yellow), C− or C+ (reddish orange), KC+ (pink or reddish orange), and Pd+ (lemon yellow or orange).

The species shows no particular substrate preference, being found on mosses, bark, wood, rock, soil and lichens. It occurs in Europe, North America, Australasia, and Greenland. The species has been recorded from both shaded and exposed locations, typically in areas with high humidity. In the British Isles, the species shows a preference for calcareous substrates, occurring on limestone, slightly calcareous sandstone, mudstone, and mica-schist, as well as artificial surfaces such as brick walls. It is particularly abundant on Old Red Sandstone cliffs in the Brecon Beacons. While primarily lithophytic, there are occasional records from dead bark. The species has been documented at various elevations, from near sea level to approximately 750 m (2,460 ft) in Britain, and up to 2,300 m (7,500 ft) in the Austrian Alps. Environmental conditions significantly influence its appearance, with specimens in more exposed locations typically displaying more clearly defined margins and paler colouration compared to those in sheltered positions. Lepraria eburnea is widely distributed across northern North America, being particularly abundant in the Great Lakes region and Maritime provinces of Canada. In these regions, it is frequently found growing as an epiphyte at tree bases in swampy areas, showing a particular preference for Thuja species. …