Type:Chile, Juan Fernandez: Robinson Crusoe Island (Masatierra), niedriger Felsrücken am Südhang von Tres Puntas, 380 m, 5-Jan-1917, Skottsberg, C. & Skottsberg, I. s.n. [S–lectotype selected by Hertel (1984), W–isolectotype].
Description.Thallus saxicolous, thick, contiguous, rimose-areolate, fissures conspicuously interlocked by their crenate edges; surface white, dull, whitish pruinose, ±smooth, very few specimens with laminal, irregularly dispersed, pustulate soralia, sometimes confluent, soredia coarse, with a distinct blackish gray to bluish tinge, pale white inside (sorediate specimens typically lack apothecia); thallus margin delimited by a thin compact, blackened prothallus line, most pronounced where different thalli meet. Apothecia sparse to numerous, circular to barely undulate, 0.2–1.2 mm in diam., initially semi-immersed, then emergent and of “lecanorine” appearance, i.e., with a whitish pruinose, biatorine margin and plane, blackened disc, with age becoming adnate, broadly sessile and distinctly lecideine with a thin, shiny, epruinose, increasingly carbonized margin and a brownish to black, convex disc, densely covered by whitish green to yellowish green pruina (C−, K−); hymenium hyaline, not inspersed, epihymenium with a diffuse aeruginose pigment (cinereorufa-green: intensifying in K, HCl+ bluish green, N+ reddish violet), with sparse clusters of small, dull brown pigment granules that dissolve in K, and with few, large, irregular, hyaline crystals persistent in K; pigmentation and hyaline granules extending to the outer exciple; proper exciple initially weakly to moderately carbonized, pigmentation intensifying with age; thallineexciple absent; hypothecium hyaline; asci clavate, Lecanora-type, ascospores 8/ascus, simple, ellipsoid to broadly ellipsoid, (7.8–)8.9–10.1(–10.3) × (3.9–)4.3–5.5(–6.4) μm (n = 19). Pycnidia immersed, ostiole blackened with brownish and aeruginose pigments (probably the same as in the epihymenium), wall hyaline; conidia shortly filiform, curved, 13.7–17.6 × ca. 1.0–1.5 μm (n = 6).
Chemistry. Thallus cortex and apothecial pruina P+ yellow, K+ yellow, KC−, C−, UV− (dull yellow); with atranorin [major], zeorin [major], leucotylin [minor], unknown terpenes [minor]; [specimens analyzed with TLC: Bungartz, F. 6411 (CDS 34626), 7280 (CDS 37764); Ertz, D. 11690 (CDS 37016)].
Ecology and distribution. Originally described from Juan Fernández Islands (Chile), also reported from coastal Chile; new to Galapagos, where it is found from the dry to the transition zone, growing on rock in ±exposed habitats.
Notes. Thalli of L. avium are superficially similar to L. austrosorediosa, in particular sorediate specimens without apothecia could easily be confused with this species or even with Caloplaca diplacia, one of the most common saxicolous lichens in the Galapagos. Differences between these three species are discussed under L. austrosorediosa. The rimose-areolate thallus surface of L. avium, where the fissures have a somewhat crenate to ±serrate margin, is also quite similar in appearance to that of L. legalloana and L. subimmersa. Lecanora avium, however, has distinctly adnate to sessile, lecideine apothecia whereas the apothecia of L. legalloana and L. subimmersa are cryptolecanorine, remaining completely immersed within areoles.