Platismatia wheeleri Goward, Altermann & Björk
Mycobank MB 517806
Thallus foliose, up to 5–10 cm across, corticate above and below; lobes ascending, loosely attached from the base, proportionately rather broad, rounded to irregular in outline, mostly 6–20 mm wide, thin. Upper surface whitish, smooth to weakly pitted, without pseudocyphellae, matt or at any rate not distinctly shiny, I–. Soredia present, fine, powdery, uniform in size, borne in continuous long marginal soralia, also sometimes present over upper or lower surface in more or less circular soralia; marginal soralia strongly sinuous even when young. Lower surface varying from brown to more often black, usually with a reticulum of narrow raised ridges, dull to occasionally shiny toward the tips, lacking rhizines or with sparse unbranched rhizines. Upper cortex 16–26 µm thick, prosoplectenchymatous; medulla white, 100–170(–200) µm thick, lower cortex 100–150 µm thick, prosoplectenchymatous, I+ purplish; photobiont cells Trebouxioid. Apothecia and pycnidia unknown. Secondary chemistry: atranorin (cortex K+ yellow) and caperatic acid (by TLC).
Platismatia is a well-known genus of 11 foliose lichens found primarily at temperate latitudes, mostly on trees (Culberson & Culberson, 1968). It is characterized by the presence of large, whitish, more or less basally attached lobes and a white to black lower surface usually without rhizines. Platismatia wheeleri was formerly included in P. glauca (L.) W. L. Culb. & C. F. Culb., a highly variable lichen recognized by its broad lobes usually with at least some marginal isidia. In some specimens the isidia grade into soralia, leading to confusion with P. wheeleri. In P. glauca, however, the soredia vary in size and at least when young bear tiny dark apical initials (eye spots), giving the supporting soralia a minutely speckled appearance at ×40. The soredia of P. wheeleri are more uniform and lack eye spots; when exposed to light, they darken uniformly across the upper surface. Additionally, soredia of P. wheeleri are borne in more or less continuous marginal soralia that are strongly sinuous from the first, while in P. glauca soralia tend to be more discontinuous and become strongly sinuous, if at all, only later during their development. Both species also bear laminal soralia, though only P. glauca produces, in addition, isidioid fruticose branches as described by Culberson & Culberson (1968) and illustrated in Brodo et al. (2001: fig. 693). The holotype specimen of P. wheeleri was sequenced in connection with a separate study on P. glauca s.lat. (Goward & Altermann, unpubl. data). The resulting sequence (ITS only) differed by eleven or more base pairs (10 sites) from 15 sequenced specimens of P. glauca available on GenBank. Platismatia wheeleri is also superficially similar to Parmotrema praesorediosum (Nyl.) Hale which differs, however, in the presence of smaller, more appressed lobes up to 10 mm across, a smooth lower surface, and production of medullary praesorediosic acid.
Platismatia wheeleri is named in honour of lichen photographer and taxonomist Timothy B. Wheeler, who first brought this species to our attention, and who contributed both the holotype and the accompanying photograph.
Currently known only from western intermontane North America, north into southern British Columbia, and south to Washington, Idaho and Oregon. All specimens seen by us were collected from the branches of Pinus ponderosa and Pseudotsuga menziesii.
Type:—U.S.A.: Montana: Missoula County, Mount Sentinel, 1 km E of the University of Montana; 45°51’N, 113°57’W, 1050 m; on branches of Pseudotsuga menziesii; Mar 2008, Wheeler 2985 (holotype UBC).
Additional specimens examined (paratypes):—CANADA: British Columbia: Fraser River Drainage: Siska Valley, 10 km S of Lytton; Goward 09-88 (UBC). Idaho: Kootenay County, Q'emlin Park, 1 km W of downtown Post Falls; Björk 14186 (UBC). Bonner County, University of Idaho Field Campus, trail to Antelope Lake, 1.5 km SE of town of Clark Fork; Björk 14255 (UBC). Washington: Spokane Co., Riverside State Park, 6.5 km NW of downtown Spokane; Björk 14132 (UBC). Shortly east of Highway 195, 43 km S of Spokane; Björk 19109 (UBC). Near intersection of Cahill and Kentuck Trails Roads, 31 km SSW of Spokane; Björk 19187 (UBC). Riverside State Park, slopes above Deep Creek, 13 km NW of downtown Spokane; Björk 19198 (UBC). Peone Prairie, near Moffat Road, 17 km NE of downtown Spokane; Björk 20081 (UBC).
Platismatiae glaucae similis sed thallii linearibus et soraliis marginalibus latis densisque differt. Isidia absunt. Apothecia et conidiomata ignotae. Corticola.