Diagnosis. A species so far collected only on bone (i.e., ‘osseo-philous’), with thalli composed of irregularly convex areoles, barely subsquamulose around their edges, their surface smooth, with a ‘waxy’, shiny texture, consistently epruinose even though appearing restricted to calcareous substrates (all Galapagos specimens exclusively collected on bone), without a distinct prothallus, apothecia distinctly sessile, disc epruinose, deeper in color than the thallus; (7.6–)8.4–13.3(–17.3) × (4.4–)5.1–6.6(–7.4) μm, with a moderately thickened, (1.7–)2.5–3.6(–4.1) μm wide septum (n = 46). The new species is reliably distinguished from other morphologically extremely similar species in Squamulea by its different ITS sequence.
Type. Ecuador, Galápagos: Santiago, summit of Cerro Gavilan, outer S-exposed crater rim, 0°12′23″S, 90°46′57″W, 840 m alt., humid zone, S-exposed, steep basalt cliffs of crater rim with ferns (Pityrograma calomelanos var. calomelanos, Polypodium tridens, Dryopteris palmata, Adiantum concinnum, Blechnum polypodioides) growing in crevices, on bone, 23-Mar-2006, Aptroot, A. 65489 (CDS 32078‒holotype; GenBank Accession number nrITS: MT967455).
Chemistry. Thallus and apothecia P–, K+ purple, C–, KC± purplish, UV– (dull); thallus and apothecia with a large proportion of parietin and smaller proportions of teloschistin, fallacinal, parietinic acid and emodin (chemosyndrome A sensu Søchting 1997).
Ecology and distribution. Currently, known only from the Galapagos, but most likely not confined to the islands. The few specimens currently known, collected on three different islands, have all been found growing on bone. In the Galapagos, bone is among the few natural substratesthat contain calcium carbonate, although only in trace amount compared to calcareous rock, which in the islands only occurs where reefs have been uplifted or as part of artificial substrates (e.g., buildings: concrete, cement, fiber cement).
Etymology. The epithet osseophila indicates that the species is so far only known to be growing on bone.
Notes. Among the Squamulea described here as new, S. osseophila is relatively well characterized by its substrate (found only on bone) and, despite growing on this calciferous substrate, nevertheless consistently forming epruinose thalli with a ± shiny, almost ‘waxy’ surface texture. Phylogenetically, the material analyzed appears to be more closely related to S. flakusii, S. loekoesiana, and S. phyllidizans than to S. subsoluta/squamosa, or the newly described S. chelonia, S. humboldtiana, and S. oceanica.