Diagnosis. Thallus containing thiophanic acid and diploicin, forming minute pale grayish olive, ±peltate verrucae that soon become conspicuously inflated and convoluted, with lecanorine apothecia that have a roughened, pruinose blackened disc, broadly ellipsoid to subglobose ascospores and pycnidia with elongate, bacilliform conidia.

Type: Ecuador. Galápagos: Isabela Island, Las Tintoreras (small island in front of Puerto Villamil at the S-coast of Isabela), 0˚58’13.6” S, 90˚57’39” W, 13 m alt., coastal zone, young lava flow of AA-lava bare of vegetation, on SW-exposed sunny, wind- and rain-exposed slope of lava piece, 10-Sept-2007, Bungartz, F. 7008 (CDS 36515–holotype).

Description. Thallus saxicolous, 0.1–3(–5.6) mm in diam., pale grayish olive, indistinctly umbilicate, of minute, scattered and widely dispersed ±peltate to ±cerebriform verrucae, closely adjoining verrucae often becoming conspicuously inflated, swollen and highly convoluted; surface dull to ±shiny, smooth, epruinose, but typically whitish eroded along the thallus folds; lacking soredia; prothallus absent. Apothecia sparse to numerous, occasionally crowded and slightly deformed by mutual pressure, circular or slightly undulate, (0.3–)0.4–1.2(–1.7) mm diam., soon becoming sessile and basally constricted, distinctly lecanorine with a thickened, entire margin, concolorous with the thallus, disc plane, with a highly roughened, finely pruinose surface; thalline exciple with cortex, photobiont layer and medulla, filled with abundant minute crystals, soluble in K (allophana-type); hypothecium not distinctly differentiated from subhymenium, pale brown, extending into the inner exciple; hymenium hyaline, not inspersed; epihymenium with a deep bluish green pigment (cinereorufa-green: intensifying in K, HCl+ bluish green, N+ reddish violet), lacking crystals (gangaleoides-type); proper exciple thin, indistinct, with few small, granular crystals, insoluble in K; thalline exciple thick, distinctly corticate, abundantly filled with small crystals soluble in K, lacking large crystals; subhymenium and hypothecium hyaline, abundantly filled with small crystals, soluble in K; asci clavate, 8-spored, Lecanora-type; ascospores simple, hyaline, smooth, broadly ellipsoid to subglobose, rarely ±ovoid, thin-walled, (4.5–)7.5–10.1(–10.8) × (4.9–)5.4–7.1(–8.8) μm (n = 45). Pycnidia immersed, flask-shaped with a colorless wall, and deep bluish green ostiole (cinereorufa-green: intensifying in K, HCl+ bluish green, N+ reddish violet); conidia simple, elongate bacilliform (‘baculiform’), (5.9–)6.8–9.8(–10.8) × 1.5–2 μm (n = 15).

Chemistry. Thallus cortex P–, K+ yellow, C+ orange, KC+ orange, UV± deep orange; medulla P−, K−, KC+orange, C+ orange, UV± deep orange; thiophanic acid [major], diploicin [minor], dechlorodiploicin [minor], isofulgidin [minor]; [specimens analyzed with TLC: Bungartz, F. 5249 (CDS 29464), 8171 (CDS 40871)].

Etymology. Named for its minutely umbilicate thallus; the Spanish “el ombligo” meaning “umbilicus”.

Ecology and distribution. Known only from the Galapagos; growing on sunny, wind- and rain-exposed lava rock, from the coast to the transition zone; easily overlooked due to its small size.

Notes. With its black discs and creamy pale thallus L. ombligulata superficially resembles Tephromela, but its asci belong to the Lecanora-type and its epihymenium color also differs from the purple, N+ red pigmentation observed in Tephromela. Because of its indistinct umbilicate growth, L. ombligulata closely resembles species of Rhizoplaca. It could be mistaken as a minute, very immature form of R. glaucophana (Nyl. ex Hasse) W.A. Weber. From that species L. ombligulata can, however, be distinguished by its unusual chemistry and the differently pigmented epihymenium (R. glaucophana contains only pseudoplacodiolic acid and it has a reddish brown epihymenium). Because thalli of L. ombligulata are so small, it is difficult to determine whether they are truly umbilicate; they may better be called peltate, with individual squamules attached at their center. Despite this growth closely resembling some thalli of Rhizoplaca, the conidia of L. ombligulata are short, bacilliform to baculiform, not filiform. The presence of xanthones in combination with diploicin is equally unusual, this secondary chemistry being unknown from species now placed in Rhizoplaca. Therefore, we decided to describe the new species not as a Rhizoplaca, but within Lecanora s.l.