Type: Brasil. Minas Geraës: Morro de Itambé, sine dato, Puiggari, J.I. 2220 (G–holotype).
Description.Thallus saxicolous or rarely corticolous (in Galapagos known only from rock substrates), thin and often reduced, rimose to verrucose areolate; surface white to pale gray, roughened, matt, epruinose or with faint, whitish pruina, lacking soredia; prothallus white, weakly developed, typically indistinct. Apothecia sparse to numerous, ±isolated or in small groups and then deformed by mutual pressure, circular to very irregular in outline, often quite large, 0.5–1.7(–2.2) mm in diam., soon distinctly sessile and usually ±constricted at the base, distinctly lecanorine, margin soon crenate and often broadly undulating, epruinose, concolorous with the thallus; disc concave to ±plane or very weakly convex, pale greenish beige, darkening with age, becoming deep brownish beige, epruinose or faintly whitish pruinose; hymenium hyaline, not inspersed; epihymenium with crystals, almost hyaline to pallid yellowish brown (elachista-brown: dissolving in K, HCl± dull greenish, N−), both pigment and crystals soluble in K (chlarotera-type); proper exciple thin, indistinct, with abundant small crystals; thalline exciple thick, ±corticate, with many small crystals that obscure a few larger ones often visible only when the small crystals are dissolved in K and the large ones persist (melacarpella-type); hypothecium hyaline; ascospores 8/ascus, simple, narrowly to broadly ellipsoid, (8.9)–9.1–11.6–(12.9) × (4.0–)5.1–6.7(–6.9) μm (n = 20). Pycnidia not seen.
Chemistry. Thallus cortex including apothecial margin react P+ yellow, C−, KC−, K+ yellow, UV−; with atranorin [major], isonotatic acid [major], 4-O-methylhypoprotocetraric acid [minor], norisonotatic acid [minor], and 2’-O-methylperlatolic acid [major]; [specimen analyzed with TLC: Bungartz, F. 7617 (CDS 38113)]. Guderley (1999) also reports ±chloroatranorin and ±usnic acid, but these substances were not detected in the Galapagos specimen.
Ecology and distribution. Neotropical (Feige et al. 2000: Argentina, Brazil, Colombia, Peru, Uruguay, Venezuela), new to Ecuador and the Galapagos; a single specimen has so far been collected in the archipelago, from a bare basalt outcrop in the high altitude dry zone of Volcán Darwin.
Notes. This species is very distinctive because of its large, strongly undulate apothecia and scant thallus; superficially it thus closely resembles L. cactacea, a species that so far is known only from cacti (see comments above). The two species are chemically well distinguished: 4-O-methylhypoprotocetraric acid is characteristic for L. subcrenulata. It is a very conspicuous secondary metabolite, easily detected by TLC [the unusual chemistry previously discussed in detail by Feige et al. (2000)].