Diagnosis. A species with small, distinctly sessile apothecia and an irregularly granular-blastidiate thallus, containing the xanthones thiophanic acid and 3-O-methylthiophanic acid.

Type: Ecuador. Galápagos: Santiago, along the trail from the caseta in La Central to La Bomba (at the coast), cerro ca. 1 km NE of the caseta and on the W-side of the trail, 0˚14’10’’S, 90˚44’41’’W, 664 m alt., transition zone, vertical, SE-exposed cliff face with ferns (Blechnum polypodioides and Pityrogramma calomelanos var. calomelanos) growing in crevices, on SE-exposed front of cliff of conglomerated basalt tuff, 25-Mar-2006, Bungartz, F. 4859 (CDS 29055–holotype).

Description. Thallus saxicolous, thin, rimose-areolate to verruculose areolate, areoles closely adjoining but not interlocked; surface pale white to ivory, roughened, matt, epruinose, in large parts forming blastidiate, pseudocorticate granules which irregularly disintegrate into large patches of ecorticate, often confluent soredia; prothallus weakly developed, powdery arachnoid to compact, indistinct. Apothecia numerous, scattered, circular to slightly irregular in outline, 0.1–0.5 mm in diam., adnate to soon sessile, distinctly lecanorine, margin persistent, smooth to soon strongly granular-verruculose, granules irregularly forming soredia, disc plane to ±convex, deep mahogany brown, epruinose; hymenium hyaline, not inspersed; epihymenium lacking crystals, with a diffuse reddish brown pigment (arnoldiana-brown: K+ dull brown, HCl+ reddish brown, N−), pigment ±persistent, although fading in K (glabrata-type); proper exciple thin, indistinct, with few crystals; thalline exciple thick, irregularly disintegrating, with abundant small crystals obscuring few larger ones, only the small crystals soluble in K, the larger ones persistent (melacarpella-type); subhymenium and hypothecium hyaline; ascospores 8/ascus, simple, ellipsoid, (10.8–)11.3–14.6(–16.7) × (4.9–)5.8–7.6(–8.8) μm (n = 30). Pycnidia immersed, ostiole brown, wall hyaline; conidia short filiform, curved, 16–20 × ca. 1.9–1.5 μm (n = 10).

Chemistry. Thallus cortex P+ yellow, K+ orange, KC+ orange, C+ orange, UV+ dull orange; with atranorin [major], zeorin [major], unknown terpenes [minor], 3-O-methylthiophanic acid [minor], thiophanic acid [major]; [specimens examined with TLC: Bungartz, F. 4852 (CDS 29048), 4859 (CDS 29055–holotype); Aptroot, A. 65570 (CDS 32158)].

Etymology. Named in honor of Charles Darwin and the Charles Darwin Foundation.

Ecology and Distribution. Known only from the Galapagos; a few collections from semi-shaded basalt tuff.

Notes. The saxicolous L. darwiniana, is so far known only from the Galapagos. It is sorediate and has a chemistry similar to L. leproplaca Zahlbr., a corticolous species reported by Guderley (1999) from Suriname and the Caribbean (Dominica). In both species the soredia are fairly coarse and often confluent, but in L. darwiniana they are formed from coarse blastidiate granules that, like verrucae, cover the entire thallus and secondarily break apart into finer soredia. This contrasts with L. leproplaca, where granular soralia initially develop within distinctly delimited soralia, which later may merge. Both species have different apothecia. Guderley (1999) referred to L. leproplaca as the sorediate counterpart (p. 210: “sorediöse Parallelsippe”) of L. tropica. The size and anatomy of apothecia in both taxa is virtually identical. Both species have an epihymenium that belongs to the glabrata-type (lacking crystals, with a diffuse reddish brown pigment not dissolving in K) and a pulicaris-type exciple. Apothecia of L. darwiniana are generally smaller (less than 0.5 mm in diam.) than those of L. leproplaca/L. tropica (typically larger than 0.5 mm in diam.). The thalline exciple of all species contains large crystals, but in L. leproplaca/L. tropica these crystals are easily observed even without polarized light. They are rarely inspersed but never obscured by smaller crystals. Guderley (1999) calls this exciple pulicaris-type. The exciple of L. darwiniana instead belongs to the melacarpella-type. Although it also contains few large crystals, these crystals are almost entirely obscured by abundant much smaller ones. And the larger crystals are difficult to see unless the smaller ones are dissolved in K. If L. leproplaca is considered the sorediate counterpart of L. tropica, L. darwiniana resembles more closely the endemic L. schindleri; both have the same exciple
type. However, the two species nevertheless differ in their substrate (saxicolous vs. corticolous), they have a different epihymenium (glabrata- vs. pulicaris-type) and the apothecia in L. darwiniana are consistently much smaller than those of L. schindleri. We therefore describe L. darwiniana here as a new species.