Type: Australia. Northern Territory: Robin Falls, 13 km SSE of Adelaide River, 13°21’S. 131°08’E, 80 m alt., sandstone boulders beside creek, in monsoon forest, 24-Mar-1986, Rambold, G. 5155 (M–holotype!, NT–isotype).
Description.Thallus saxicolous, thin to strongly thickened, rimose to rimose-areolate, fissures with undulating to very weakly crenate edges, closely adjoining but not interlocked; surface pale bluish gray to pale greenish grey to ivory or grayish white, smooth and epruinose to ±roughened with a coarse, whitish pruina, with pustulate soralia producing white, coarsely granular soredia, without a blackish or bluish hue (see notes below); thalline margin confluent with other, compatible thalli or distinctly delimited by a compact, blackened line, or, where growing unhindered, radiating into a fimbriate, white prothallus. Apothecia sparse to numerous, circular to barely undulate, dispersed to loosely aggregated, rarely closely grouped and deformed (‘gall’-like), 0.1–0.8(–1.0) mm in diam., adnate to soon sessile, biatorine, initially pallid, waxy, pale creamy beige, but becoming partially discolored with age, ±blackened (as if covered in soot), occasionally even young apothecia distinctly blackened and then of lecideine appearance, mostly epruinose, rarely the margin whitish pruinose, disc concolorous to slightly darker in color, pallid, pale creamy beige to blackened, disc and margin C−, K−; hymenium hyaline, not inspersed, epihymenium colorless to brownish, C−, K−, at least in part with diffuse, aeruginose pigment (cinereorufa-green: intensifying in K, HCl+ bluish green, N+ reddish violet), this pigmentation eventually permeating the entire exciple, the overall concentration nevertheless remaining low, the exciple not carbonized (i.e., not becoming brittle from increasing pigmentation), anatomy biatorine, not truly lecideine, inner exciple and hypothecium filled with small, colorless crystals, dissolving in K; hymenium hyaline, not inspersed; thalline exciple absent; asci clavate, Lecanora-type, ascospores 8/ascus, simple, narrowly to broadly ellipsoid, (7.8–)9.9–12.1(–12.7) × (3.9–)4.6–6.0(–6.9) μm (n = 30). Pycnidia immersed, ostiole blackened (brownish and aeruginose pigment), wall hyaline; conidia shortly filiform, ±curved, 13.7–16.7 × ca. 1.0–1.2 μm (n = 5).
Chemistry. Thallus cortex P+ yellow, K+ yellow, KC–, C–, UV– (dull yellow), medulla P+ yellow, K+ yellow, KC–, C–, UV± pale yellow; with atranorin [major], ±2’-O-methylhyperlatolic acid [major, minor or trace], ±zeorin [minor or trace]; the chemistry is apparently a little variable, specimens with 2’-O-methylperlatolic acid [major] and 2’-O-methylsuperlatolic acid [minor or trace] are also known [specimens analyzed with TLC: Bungartz, F. 4398 (CDS 28483), 4612 (CDS 28699), 6942 (CDS 36446), 7885 (CDS 38394), 9355 (CDS 46642)].
Ecology and Distribution. Previously considered endemic to Australia, new to Ecuador and the Galapagos, where it is one of the most common saxicolous species, frequently growing together with Caloplaca diplacia (Ach.) Riddle, in dust-rich, ±nitrophytic habitats, on rocks close to the ground, from the coastal zone throughout the dry and transition zones into the humid zone.
Notes. In Galapagos specimens of L. austrosorediosa have regularly been misidentified because of their striking similarity with Caloplacadiplacia. Sectioning apothecia clearly reveals that this species does not belong to the Teloschistaceae because it has simple spores formed in typical Lecanora-type asci. Sterile material can also be distinguished since the pustulate soralia of L. austrosorediosa are white, never tinged dirty bluish green as in C. diplacia, their rimose to rimose-areolate thalli are typically pale, grey to greenish grey or almost white whereas the distinctly areolate to subsquamulose thalli of C. diplacia are deep lead- to olive-grey. Of course secondary chemistry also distinguishes the two species: although both contain atranorin, C. diplacia contains isofulgidin, vicanicin and caloploicin whereas L. austrosorediosa instead contains ±2’-O-methylhyperlatolic acid (or closely related secondary metabolites) and zeorin.