Lecanora achroa
Description : Thallus continuous to rimose, yellowish grey to greenish grey, epruinose, without soredia. Prothallus blackish brown. Apothecia sessile, 0.3–0.8 mm diam., discs orange-brown, epruinose to slightly grey-pruinose. Margins concolorous with thallus, thin to thick, smooth, entire to verruculose, persistent to excluded. Cortex hyaline, inspersed with small crystals, 15– 35 μm thick. Amphithecium with large crystals, not dissolving in K (pulicaris -type). Parathecium hyaline, with crystals, 10 μm thick. Epithecium yellowish brown, colour rapidly dissolving in K, with crystals (chlarotera -type) rapidly dissolving in K, 10–15 μm thick. Hypothecium hyaline. Paraphyses slightly swollen apically. Ascospores ellipsoidal to broadly ellipsoidal, 10.5–16.5 × 6.5– 8.5 μm.
Chemistry : Major compounds: ±atranorin, ±2'- O- methylperlatolic acid and usnic acid; Minor compounds: ±atranorin, chloroatranorin, ±arthothelin and unidentified triterpenoids.
S: Canterbury (Hagley Park, Christchurch). On ash trees in urban park (Galloway et al. 2001a: 28–29). Known also from North and South America, Indian Ocean islands, Oceania and Australia (Lumbsch et al. 1995; Guderley 1999; McCarthy 2003c, 2006; Lumbsch & Elix 2004: 18; Ryan et al. 2004b: 188).
Palaeotropical
Ilustrations : Lumbsch et al. (1995: 564, fig. 1); Guderley (1999: 175, fig. 13A).
Lecanora achroa differs from L. helva in having relatively small apothecia with orange-brown discs, by the more greenish colour of the thallus, the rougher thallus surface and the presence of usnic acid. L. helva contains the 2'- O- methylperlatolic acid chemosyndrome, while L. achroa often contains no further phenolic substances in addition to atranorin and usnic acid.
