Diagnosis. A pale yellowish green to yellowish white, densely pruinose, continuous crust, that, when well developed, forms conspicuously cerebriform thalli with abundant pulvinate-pustulate soralia, rarely forming apothecia; containing usnic acid and abundant terpenes (forming a ‘fur’ of crystals with storage), occasionally also with xanthones.

Type: Ecuador. Galapagos: San Cristóbal, Cerro Partido along trail from entrance to Cerro Pelado to El Ripioso, 0˚51’23’’S,
89˚27’37’’W, 376 m alt., transition zone, rocky SW-exposed slope of hill with Jasminocereus thouarsii, Clerodendrum molle var. glabrescens, Psidium galapageium, Bromeliaceae and ferns growing in rock crevices, on W-exposed front of basalt boulder, 28-Apr-2007, Bungartz, F. 6596 (CDS 34816–holotype).

Description. Thallus saxicolous, contiguous, not distinctly fissured, uneven to verrucose (‘lumpy’), thin to markedly thickened and then convoluted, gnarled, soon becoming conspicuously cerebriform, particularly in the center i.e., with conspicuously inflated, swollen and convoluted protuberances, which may be dispersed or merge into a very thick crust; surface pale yellowish green to yellowish white, dull, with a coarse, yellowish green pruina (with prolonged storage developing a fine fur of whitish terpenoid needles, appearing moldy), soralia abundant, pulvinate-pustulate, with farinose, bright greenish yellow soredia, sometimes confluent and covering the entire thallus; prothallus absent. Apothecia very rarely present, sparse, circular or slightly undulate in outline, 0.6–1.5(–1.8) mm in diam., adnate to sessile, distinctly lecanorine with a yellowish pruinose, ±crenate margin soon disintegrating into soredia, concolorous with the soredia and/or thallus; disc plane to barely convex, greenish beige, densely whitish pruinose; hymenium hyaline, not inspersed, epihymenium with a diffuse, dull brown pigment (elachista-brown: dissolving in K, HCl± dull greenish, N−) and few to abundant minute crystals, mostly dissolving in K (residue of fine, rounded, reddish granules persistent, 0.5–1 μm); proper exciple thin, indistinct, with few small crystals; thalline exciple densely filled with small crystals that entirely dissolve in K; subhymenium and hypothecium hyaline; asci clavate, Lecanora-type, ascospores 8/ascus, simple, narrowly to broadly ellipsoid, (3.9–)4.1–5.2(–5.9) × (6.9–)8.2–11.8(–13.7) μm (n = 30). Pycnidia not seen.

Chemistry. Thallus cortex including apothecial margin P−, C– or C+ orange, KC– or KC+ orange, K± yellowish brown, UV− (dull); usnic acid [major], ±arthothelin [major], zeorin [major], ±leucotylin [minor], unknown terpenes [minor or traces];[specimens analyzed with TLC: Aptroot, A. 64123 (CDS 30685); Bungartz, F. 4794 (CDS 28926), 5389 (CDS 29605), 6564 (CDS 34782), 6724 (CDS 34968), 7133 (CDS 37618)].

Etymology. Like L. cerebriformis described above, the epithet cerebrosorediata refers to the unusually convoluted, brain-like growth form as well as the presence of soredia.

Ecology and distribution. Known only from the Galapagos, a common saxicolous species, particularly frequent in coastal, dry and transition zone vegetation, less common in the humid zone, typically growing in exposed, sunny, occasionally ±sheltered habitats.

Notes. Because of its cerebriform growth, this species could be considered a yellowish, sorediate counterpart of the white L. cerebriformis and containing usnic acid rather than protocetraric acid. The cerebriform growth of these two not ecessarily closely related species might be the result of an adaptation to a habitat as the two species are often found growing together. The most exuberant thalli of both species are frequently encountered in humid habitats (shaded cliffs, sheltered fronts and overhangs of large boulders). Thalli of L. cerebriformis lacking conspicuous protuberances are rare, but rimose thalli of L. cerebrosorediata are fairly common. They typically grow in drier, more exposed sites. These specimens were initially believed to be a distinct species, but intermediates do occur and the two forms are chemically identical, predominantly producing usnic acid but occasionally additional xanthones.