Type:—EAST ASIA. Singapore: Sembawan Park, on N-coast, 2m alt., grassland with scattered trees and shrubs, on tree trunk (Cassia fistula, 80 cm in diam). within reach from the ground, 25 Nov 2000, Sipman, H.J.M. 46399 & Tan, B.C. [B–Holotype (non vidi); SINU–isotype (non vidi)].
Thallus saxicolous, terricolous, among bryophytes or plant debris, rarely corticolous, aggregating, i.e., initially of dispersed, scattered, isolated granules or small granule clusters, adhering to their substrate by scarce protruding hyphae forming an indistinct prothallus, secondarily aggregating to become contiguous (close to the alpina-type sensu Lendemer 2011a); surface yellowish green, color barely fading and ±persistent in the herbarium; hypothallus inconspicous, exposed only as a fine prothallus along the thalline granules; rhizohyphae absent or indistinct; granules initially small, ecorticate with sparse, short protruding hyphae [(40–)70–170(–200) µm in diam., very uneven in size], soon pseudocorticate, compact, becoming very coarse to almost subsquamulose [(220–)245–420(–580) µm in diam.]; then secondarily forming soredia. Apothecia very rare (not observed in the Galapagos specimens), initially pale, whitish, waxy, soon deep brown to blackened, but usually not strongly carbonized, initially rounded, with age becoming waved to irregular in outline, often closely grouped and becoming deformed, margin lecideine-biatorine, persistent, not excluded with age, disk plane, expanded, not becoming convex with age; proper exciple reddish brown throughout, most strongly pigmented along the outside, textura oblita; epihymenium deep reddish brown; subhymenium and hypothecium reddish brown; hymenium hyaline; paraphyses slender, barely branched, apically swollen, with a brown pigment cap; asci clavate, with a fuzzy IKI+ deep coat and a tholus with an IKI+ blue inner tube (Byssoloma-type); ascospores 8 per ascus, but often only 2–3 maturing, hyaline, narrowly ellipsoid, often slightly bent, 3-septate, not constricted at the septa, (18.0–)20.7–27.6(–28.0) ´ (4.0–)4.6–6.2(–7.0) µm (n = 20). Pycnidia not observed. Photobiont green, coccoid, 7–10 μm in diam.
Distribution and ecology: Pantropical (Saag et al. 2009); newly reported from the Galapagos; the most common truly leprose species in the Galapagos with a wide ecological amplitude, from the dry through the transition zone into the humid zone, on rock or soil, rarely on bark, typically in ±sheltered, semi-shaded to shaded cavities, vertical fronts, or below overhangs, rarely ±exposed, but typically not receiving direct sunlight.
Notes: Lendemer & Hodkinson (2013) recently published the new monotypic genus Nelsenium to accommodate “Lepraria” usnica. This genus was named in honor of Matthew P. Nelsen who previously demonstrated that this species belongs to the Pilocarpaceae (Nelsen & Gargas 2008; Nelsen et al. 2008) unlike Lepraria s.str., which belongs in Stereocaulaceae.
The fertile material of “Lepraria” usnica from Ecuador examined here, clearly indicates, that this species is best placed in Septotrapelia, a genus recently described in Pilocarpaceae by Aptroot et al. (2006). Septotrapeliausnica has lecideine-biatorine apothecia with narrowly ellipsoid ascospores just like the type species of Septotrapelia, S. glauca (2007: 128). The unique thallus morphology of “Lepraria” usnica also suggest that this species belongs to Septotrapelia. Although initially strictly leprose and composed of minute, compact granules (alpina-type sensu Lendemer 2011a), these granules eventually become quite large and have a microsquamulose appearance. Strictly speaking these bullate to microsquamulose granules are no longer truely leprose, because the granules often produce secondary soredia. These well developed granules are structurally extremely similar to thalli of S. glauca, although this species forms squamules that are much larger (up to 2000 µm wide) than the well developed granules of “Lepraria” usnica (max. 200 µm wide).
Because of this unique morphology, we are convinced that both the fertile specimens from continental Ecuador and the sterile thalli collected in Galapagos are conspecific with “Lepraria” usnica s.str. Even the sterile material is very distinct with its coarse granules that form secondary soredia and always contain usnic acid.
With the new combination proposed above, the genus Nelsenium Lendemer & Hodkinson (2013: 1013) becomes a synonym of Septotrapelia.
To clarify the species concept, it would be helpful to select an epitype from fertile specimens, but the holotype of “Lepraria” usnica was collected in East Asia (Singapore) while the fertile material examined here originates from mainland Ecuador. As it is possible that fertile material from Singapore may eventually be found, it would be preferable to select such the epitype from there.
Saag et al. (2009) characterize the distribution of “Lepraria” usnica as circum-tropical, ranging from Central and South America, Australia, southern and south-eastern Asia (Singapore, Sri Lanka) to southern Africa. Ultimately molecular studies on specimens from all these regions will be needed to determine whether Septotrapeliausnica is indeed as widely distributed as the current species concept implies.
The material of “Lepraria” usnica used for the molecular studies was collected in Australia and Indonesia (Nelsen & Gargas 2008; Nelsen et al. 2008). These sequences, which confirmed placement of this species in Pilocarpaceae, were subsequently used by Lendemer & Hodkinson (2003) to justify the new genus Nelsenium. Therefore, strictly speaking only the Australian and Indonesian specimens belong to Nelsenium s.str., a genus defined by Lendemer & Hodkinson (2003) based on an allele sequence different from that of Fellhanerabouteillei (Desm.) VÄ›zda (1986: 214).
Although future molecular studies may ultimately show that specimens from these geographically disjunct regions belong to several cryptic species within Septotrapelia, given, that the thalli of S. usnica are morphologically so distinct and chemically identical, it is highly unlikely that these specimens belong in different genera.
Aptroot et al. (2006) previously suspected that the sterile Galapagos material of this species belonged in Septotrapelia, but that this species was undescribed. During his visit to Galapagos, Aptroot identified the material he collected as two different species, suggesting that only specimens at CDS with the most minute granules were “Lepraria” usnica, and that specimens with larger granules belonged to “Septotrapelia sp. nov.”. All the material is, however, chemically uniform, containing only usnic acid and zeorin. The size of the granules clearly varies considerably. Comparing all specimens with the fertile exsiccatae material it became evident, that the species is morphologically quite variable in granule size; thalli begin their growth from minute soredia, develop into larger, pseudocorticate granules that secondarily form soredia and when particularly well developed these granules even develop apothecia. The exsciccatae specimen is abundantly fertile, growing on soil and must have been collected in ideal growth conditions since the thalli are so well developed and fertile. No such material has been found in the Galapagos.
In the absence of fertile specimens it is not surprising that the species was described as a Lepraria (Sipman 2003, 2004). Molecular studies previously demonstrated that it belongs to the Pilocarpaceae (Nelsen & Gargas 2008; Nelsen et al. 2008), which is consistent with its transfer here to Septotrapelia.
A second species, morphologically very similar, but with granules of more homogenous size and more bluish green color, represented in CDS by two collections only, also appears to be present in Galapagos. It is chemically distinct containing oxodidymic acid and its accessories (for details about these secondary metabolites see Johansson et al. 2005), substances known from Letrouitia and Bapalmuia, another genus in the Pilocarpaceae (unpublished data by J. A. Elix). This species will not described until more material is available.