Taxonomic note. The name is here applied in the widest sense. Material includes both specimens that more closely resemble the barely squamulose morphotypes of S. subsoluta s.str., as well as others that are distinctly squamulose and thus more closely resemble S. aff. squamosa. Although some Galapagos material phylogenetically seems to be part of S. subsoluta s.str., most specimens are part of various different other clades. They cannot presently adequately be assigned to any named taxon within Squamulea.
Description. Thallus very variable, areolate to indistinctly subsquamulose, up to 3 cm in diam., but several thalli often merging, often confluent, individual areoles flattened to barely convex, edges mostly turned downward, areoles loosely dispersed to aggregating into small groups with few immersed to adnate apothecia, effuse, not delimited by a prothallus, hypothallus absent; surface smooth, ± waxy, but not shiny, pale yellow orange to deep orange, epruinose; very rarely sorediate; soralia erumpent, 0.1–0.3(–4) mm in diam., occasionally confluent, irregularly extruding deep orange or deep yellow, granular soredia (35–50 μm in diam.). Apothecia numerous, dispersed to ± aggregated, sometimes crowded, sessile, up to 0.6 mm in diam., lecanorine; thalline margin persistent, not excluded, slightly prominent, regularly circular, not flexuose, almost level with disc, (40‒)60‒80 μm thick, concolorous with thallus, epruinose, rarely whitish pruinose in parts, C-, K+ purple; disc flat to slightly convex, deep orange, darker than the margin, mostly epruinose, rarely faintly whitish pruinose in parts, C-, K+ purple; epihymenium with orange pigment granules, C+ red, K+ purple, pigmentation contiguous with the outer exciple, hymenium hyaline, not inspersed; proper exciple absent (completely reduced); thalline exciple differentiated into an inner, hyaline part, a central part with large trebouxioid photobionts, lacking crystals (or rarely with very few, small crystals, dissolving in K), and an outer, deeply brownish orange part, with abundant pigment granules, C+ red, K+ purple; subhymenium and hypothecium not differentiated, hyaline, not inspersed, paraplectenchymatous, with large, rounded to ± angular cells; asci broadly to narrowly clavate, Teloschistes-type; ascospores 8/ascus, polaribilocular, oblong to narrowly or broadly ellipsoid to almost globose often with slight median swelling at the septum, (7.5–)8.4–13.3(–17.3) × (4.0–)5.2–7.0(–7.8) μm, with a moderately thickened, (1.7–)2.5–3.9(–5.0) μm wide septum (n = 90). Pycnidia not observed.
Chemistry. Thallus and apothecia P–, K+ purple, C–, KC± purplish, UV– (dull); thallus and apothecia contain high proportions of parietin and lesser proportions of teloschistin, fallacinal, parietinic acid and emodin corresponding to chemosyndrome A sensu Søchting (1997); some specimens analyzed correspond to chemosyndrome A3 sensu Søchting (1997).
Ecology and distribution. Squamulea subsoluta, as currently delimited, has a world-wide, cosmopolitan distribution, unlike its similar counterpart Squamulea squamosa (B. de Lesd.) Arup, Søchting & Frödén, which Wetmore (2003, 2007a) suggests is restricted to southwestern North America. In Galapagos, S. subsoluta s.l. is common throughout all vegetation zones, often growing in nutrient-rich situations and then frequently blackened by cyanobacteria growing in between its thallus areoles.
Notes. Our current phylogenetic analysis was unable to clearly resolve the different groups of Squamulea squamosa/subsoluta. Although we included in our analyses numerous specimens also from outside Galapagos, the resolution of this group remains taxonomically challenging. Most specimens cited below belong to the typical morphotype of S. subsoluta: their thalli are thin, poorly developed, composed of ± angular to barely subsquamulose epruinose areoles, without a distinct pro- or hypothallus. Some of these specimens appear phylogenetically more closely related to S. loekoesiana than to S. subsoluta s.str. Morphologically, all specimens are not clearly distinguished from the phylogenetically distinct S. chelonia, S. humboldtiana, and S. oceanica. Few specimens in Galapagos have a more distinct squamulose morphology. In our phylogenetic tree, these specimens (labeled ‘squamosa 2 & 3’) appear closely related to S. squamosa s.str. The specimens, however, do not belong to the same clade and as soon as more specimens from a broader geographic range are included the resolution of the phylogenetic tree breaks down; relationships then appear much less clearly resolved. Additional specimens of a much broader scope, including additional genes, are necessary to better understand this group. Virtually all Galapagos specimens of S. squamosa/subsoluta s.l. lack soredia. One sorediate collection, however, is assigned here with some hesitation to S. squamosa/subsoluta s.l. Nevertheless, the only two specimens (COLO 294630, duplicate at QCA) cannot be considered to be conspecific with S. phyllidizans as their morphology clearly does not agree with that species. The material instead has a deep orange thallus composed of irregularly subsquamulose areoles; it is not distinctly squamulose and only very sparsely sorediate, but not blastidiate. Unfortunately, this historic collection turned out to be too old to yield DNA (specimens collected on 25-Apr-1976 by Weber, W.A. s.n. & Lanier, J., L-62891, COLO 294630, duplicate at QCA).