Diagnosis: Similar to Diploicia glebosa but differs in having a much rougher, white to grey upper surface that is usually strongly and coarsely pruinose and more flattened, with less convoluted lobes.
Type: Ecuador, Galapagos, Santa Cruz, along shore E of Puerto Ayora near Charles Darwin Research Station, 0˚44’45''S, 90˚17’39''W, 20 m alt., coastal zone, barren coastal cliffs, growing on basalt, 29 May 2005, Aptroot 63280 (CDS 30020−holotype).
Description: Thallus saxicolous, crustose to subfoliose, placodioid, with elongate, sometimes slightly convex, rarely convoluted, contiguous areoles in the centre, but radiating, contiguous, fan-shaped, apically broadened, flattened marginal lobes; surface white to greyish white, rarely ±cream coloured or with a faint pinkish tinge, but not beige or brownish, often conspicuously darkened along the lobe margins (tan to dark grey or blackened), usually dull, with a conspicuously roughened texture, rarely ±smooth, completely and evenly covered by moderate to very strong, coarse to very coarse pruina, pruina especially pronounced along the lobe margins; central areoles often sorediate or only with apothecia, rarely with both; soralia, when present, convex, erumpent, circular to irregular, occasionally ±confluent, developing from the thallus surface, soredia white, but often with a pinkish to dark grey tinge, granular, compact, ecorticate with sparse, short protruding hyphae [(45–)61–85(–106) µm in diam.]; cortex phenocorticate, with a 7.5–10 µm thick epinecral layer, interspersed with fine crystals (most, but not all dissolving in K) and a pale pinkish brown pigment (± persistent in K), phenocortical layer prosoparenchymatous (ca. 10 µm wide) filled with minute crystals (soluble in K) and a few dead algal cells, with the photobiont layer below; medulla of densely interwoven hyphae, white throughout, rarely dirty orange brown near the substrate (unidentified secalonic acid derivates), IKI-, filled with minute crystals that dissolve in K and sparse, large crystals that are insoluble in K, usually not forming needles in H2SO4 (only one specimen collected on limestone rather than lava contained calcium oxalate and formed characteristic colourless needles in H2SO4). Apothecia emergent, soon sessile, disc black, typically epruinose to very faintly pruinose, rarely with a bluish tinge caused by a dense white pruina; initially lecideine with a thin proper margin, soon lecanorine, engulfed in and obscured by a thick, often ±discontinuous thalline margin which becomes irregularly crenate with age; thalline exciple with cortex, indistinct photobiont layer and medulla, filled with abundant minute crystals (same reactions as the thallus); proper exciple initially conspicuous, dark brown to strongly carbonized, progressively reduced with age, fading to brown or even hyaline, extending from a deep, fuscous brown, or very rarely reddish brown hypothecium that extends into a short, fuscous brown to rarely reddish brown stipe at the base; subhymenium not distinctly differentiated from hypothecium, inspersed with few, inconspicuous oil droplets; hymenium hyaline, not (or very sparsely) inspersed with a few oil droplets; epihymenium olivaceous, interspersed with hyaline to brownish granules and a diffuse, dull greenish pigment (K+ violet), paraphyses with brownish pigmented caps; asci clavate, 8-spored, similar to the Bacidia-type (central, unstained part ±cylindrical, but stained flanks merging at the tip); ascospores 1-septate, soon deep olive brown, smooth, ellipsoid to narrowly ellipsoid, often with ±pointed ends, with moderate median and initially indistinct but soon distinct apical thickenings, cell lumina initially ±angular, but becoming thin-walled with age (±Dirinaria-type), (11–)14–18(–22.5) × (5–)6–7.5(–9) mm (n = 73), spore wall smooth, not ornamented. Pycnidia immersed, flask-shaped with colourless wall, and deep fuscous to olivaceous ostiole; conidia simple, bacilliform (slightly tapered at one end') (4–)4.5–5.5(–6) × ca. 1–1.5 mm (n = 10).
Chemistry: Thallus P+ yellow, K+ yellow, C−, KC−, UV- (dull yellowish); medulla P-, K-, KC-, C-, UV- (dull yellowish); atranorin (minor), chloroatranorin (minor or trace), diploicin (major or minor), dechlorodiploicin (major or minor), dechloro-O-methyldiploicin (trace), O-methyldiploicin (trace), buellolide (major), norbuellolide (major), fulgidin (minor), isofulgidin (minor or submajor), norcanesolide (minor), rarely also with unknown secalonic acid derivatives (minor).
Etymology: A Neotropical species (presently known only from the Galapagos, but possibly more widely distributed in the Neotropics, see below).
Ecology and distribution: This species occurs from the coastal to the lower transition zone, in sunny to semi-shaded, rarely ±shaded, mostly wind- and rain exposed habitats like the top of boulders or the front of cliffs; one specimen was collected from limestone from an ancient marine deposit, uplifted above the sea, a substrate rarely found in Galapagos (Aptroot, A. 64356, CDS 30921).
Notes:Diploicia neotropica is a morphologically variable species and three different forms can be distinguished informally: the first is strongly pruinose with bright white, somewhat 'frosted' thalli with densely pruinose apothecial discs with a bluish tinge. This morphotype is typically fertile, although a few specimens are also sorediate. The second, more common morphotype has weakly pruinose thalli with a faint pinkish surface and typically epruinose or faintly pruinose discs. Usually these thalli have both soredia and apothecia, although apothecia may be sparse or even absent in some specimens. Both forms have ±flattened marginal lobes with increasingly coarse pruina towards their tips. The lobes usually have darkened (fuscous) margins. These moderate to densely pruinose morphotypes of D. neotropica can readily be distinguished from the shiny, epruinose thalli of D. glebosa. Unfortunately, pruina are not completely absent from all forms of D. glebosa. Although specimens of D. glebosa are generally very uniform in their appearance, a few have fine, faint, white pruina. Where such pruina covers the surface, the otherwise shiny cortex appears dulled. These specimens could then be confused with a third morphotype of D. neotropica with fine, less abundant pruina. Nevertheless, these superficially similar thalli can be distinguished even when they grow in close proximity.
Despite their variability, all morphotypes of D. neotropica are characterized by a surface which remains bright white or rarely has a faint pinkish hue, and these specimens do not darken even with prolonged herbarium storage. All have a roughened, distinctly pruinose surface. Even if pruina of D. neotropica varies from fine to coarse, faint to abundant, it covers a distinctly roughened surface and, unlike D. glebosa, the upper surface of D. neotropica is never shiny.
These differences in pruinosity, texture and colour are conspicuous, but a detailed examination of the cortical anatomy of the two species failed to reveal any correlating differences. The internal cortical structure, the presence, size and distribution of crystals is similar in both species. In section the outer cortex of both species is typically pale brown, even if in specimens of D. neotropica with a bright white, strongly pruinose thallus. We suspect that the cortical pigments are different, because only specimens of D. glebosa darken conspicuously on prolonged storage. Nevertheless, pigment concentrations are generally so low that the alternative reactions in K and HNO3 (following Meyer & Printzen 2000) were not observed.
Thalli of D. glebosa are typically not sorediate and usually abundantly fertile, whereas those of D. neotropica display greater variation. Most have abundant soredia with many, few or no apothecia, but a few are abundantly fertile with sparse or no soredia.
The considerable morphotypical variation of D. neotropica is reflected by an equally diverse chemistry. Unfortunately the chemical variations did not correlate with the three morphotypes described above.