Type: Ecuador. Galapagos Islands: Isla Santiago: summit of Cerro Gavilan, inner N- and NE-exposed crater rim, ) 12º20’0”S, 90º47’3” W, 840 m, humid zone N- and NE-exposed, steep basalt cliffs of crater rim with ferns (Pityrogramma calomelanos var. calomelanos, Polypodium tridens, Dryopteris palmata, Adianthum concinnum, Blechnum polypodioides), growing on lava rock in crevices, Aptroot, A. 65667 (CDS 32258! holotype).
Diagnosis. Similar to Myriospora hassei, but distinguished by emergent apothecia that are occasionally covered with coarse orange pruina and, with maturity, develop a distinctly elevated thalline margin, which increasingly blackens from the inside.
Etymology. The species is named in honor of lichenologist and taxonomist Martin Westberg of Sweden in honor of his excellent revision of the genus Myriospora.
Description. Thallus of dispersed to closely adjoining,±circular to irregular areoles, individual areoles broadly attached, ca. (0.3)0.7-1(-2) mm in diam., ±subsquamulose, indistinctly lobate along the margin; surfacewhitish to pale brown, dull, even to ±irregular, but not conspicuously verrucose, epruinose. Cortex differentiated into a ca. 25 µm thick epicortex of prosoplectenchymatous conglutinated cells, hyphae irregularly interwoven, not distinctly orientated, not becoming necrotic, followed by a eucortex, divided into an outer, ca. 5-15 µm thick, prosoplectenchymatous, deep brown pigmented part, and an inner, ca. 30-45 µm thick, prosoplectenchymatous, hyaline part (all layers devoid of crystals), the outer pigmented part often fading or indistinct in the thallus areoles, but strongly pronounced and best developed in the thalline margin of the apothecia; photobiont layer discontinuous, especially towards the center of the areoles interrupted by bundles of hyaline hyphae (ca. 10-20 µm) wide, which conspicuously divide this layer into ‘islands’ or ‘packets’ of photobiont cells (ca. 20-60 µm wide); photobiont cells trebouxioid, ca. 8-12 µm in diam.; medulla of loosely interwoven hyphae, continuous with attachment hyphae below.
Apothecia one (or rarely two) per areole, at first immersed, cryptolecanorine, but soon emergent and almost lecanorine, with a distinctly elevated thalline margin, though not becoming sessile; disk at first punctiform to ±urceolate, soon dilating, expanding and becoming concave to barely convex, deep reddish brown, epruinose or rarely covered by a coarse, orange, crystalline pruina (K–, crystals dissolving); margin at first inconspicuous, barely elevated, concolorous with the thallus surface, pigmentation pale due to the thick hyaline epicortex, and at maturity epicortex of the prominent margin increasingly abraded, the margin thus darkened to almost blackened. Thalline exciplewell developed, conical, at the base ca. 250-350 µ wide and filled with clusters of photobiont cells surrounded by densely interwoven hyphae, towards the apex tapering, ca. 50 μm wide, photobiont cells and medullary hyphae disappearing, apical part distinctly stratified into an innermost hyaline part, a central, deep brown layer and the outer, hyaline epicortex; proper exciple reduced, barely differentiated from the innermost, hyaline part of the thalline exciple; epihymeniuma diffuse ca. 20-30 µm wide, pale orange brown pigmentation of the upper paraphyses; hymenium ca. 125-150 µm high, not inspersed, paraphyses at mid-level ca. 1.5 µm wide, apically not significantly wider, not conspicuously swollen. Asci clavate, ca. 30 ´ 8 µm, polysporous (more than 100 spores per ascus);ascospores hyaline, non-septate, oblong(3.5-)4(-4.5) ´ca. 2 µm (n = 35).;subhymenium and hypothecium not distinctly differentiated, laterally extending into the proper exciple, in the center up to 200 µm thick, sparsely inspersed with tiny oil drops (ca. ca. 1-2 µmin diam). Pycnidia punctiform, urceolate to flask-shaped, wall unpigmented, sometimes adjoining, ostiole colored by a diffuse, brown pigment, conidigenous cells c. 10 ´ 1 µm, conidia subglobose, ca. 2 x 1.5 µm (n = 20).
Chemistry. All spot tests negative, no secondary metabolites detected.
Distribution and Ecology. The only two specimens collected in Galapagos are both from the summit area of Cerro Gavillan in the humid zone of Santiago Island, where the lichen grows among ferns on steep N- to NE-exposed basalt cliffs of the crater rim.
Differentiation. The taxonomy of Myriospora is well supported by the phylogeny of Wedin et al. 2009 and often relatively small differences in similar suites of characters occur between species (Westberg et al. 2011). This makes many of the species in the genus appear very similar. Until Westberg et al. (2011) most species recognized today were thought to be variations of Acarospora smaragdula (Wahlenb. ex Ach.) A. Massal. (Knudsen 2004 & 2007; Westberg et al. 2013).
Two species, Myriospora hassei and M. scabrida, known from the coast of southern California (Knudsen 2007) and look very similar to the newly described M. westbergii from the Galapagos. Myriosporascabrida also forms elevated apothecia, but its apothecial margin is formed by hyphae of the proper exciple and this margin does not become distinctly blackened around the disk.
While M. westbergii shares the overall appearance of M. hassei, it forms very similar, pale, subsquamulose areoles with initially punctiform to urceolate apothecia, the two species can nevertheless easily be distinguished when well developed, because M. westbergii then forms emergent apothecia with a conspicous thalline margin, initially with a narrow blackened, inner rim, that pigmentation eventually extending across the whole margin. In contrast, the apothecia of M. hassei always remain immersed and often punctiform, rarely becoming urceolate.
Myriospora hassei is considered endemic to western North America (Knudsen 2007 &2011). Although it has been reported from in Europe (Roux & Navarro-Rosines 2011), we have recently found specimens on San Clemente Island (Knudsen 16684 & Howe, UCR) that clearly show the tendency of this lichen to develop lichenicolous, parasitic on Acarospora socialis H. Magn., a species not known from Europe. The distribution range of M. hassei in California closely matches that of A. socialis along the coast of California (see distribution map in Knudsen 2011) and it seems likely that M. hassei only grows where it can establish on the thalli of A. socialis.
Myriospora rhazagida (Nyl.) M. Westb., a species that occurs along the Atlantic coasts of North America and Europe, is also similar, but it differs in having immersed apothecia surrounded by a wide black ring around its disk, formed by the expansion of hyphae of the proper exciple. In M. westbergii the black pigmentation of the margin is clearly part of the cortex and thus hyphae of the thalline not the proper exciple. In the genus, orange to rust-red pruina have otherwise been reported only from M. dilatata (M. Westb. & Wedin) K. Knudsen & L. Arcadia, a montane species that occurs along rivers and lakes of northern Sweden (Westberg et al. 2011).
Additional specimens examined (paratypes). – ECUADOR. GALAPAGOS ISLANDS: Isla Santiago: summit of Cerro Gavilan, inner N- and NE-exposed crater rim, 0°12’20”S, 90°47’3”W, 840 m, humid zone N- and NE-exposed, steep basalt cliffs of crater rim with ferns (Pityrogramma calomelanos var. calomelanos, Polypodiumtridens, Dryopteris palmata, Adianthum concinnum, Blechnum polypodioides), growing on lava rock in crevices, Bungartz, F. 4762 (CDS 28894), Aptroot, A. 65672 (CDS 56106).