TYPE. UNITED STATES. Washington: Spokane County, Riverside State Park, 6.5 km NW of downtown Spokane, 47˚42’N, 117˚30’W, 525 m, on branches of Pinus ponderosa, July 2009, Björk 19340 (UBC, holotype; B, CANL, GZU, isotypes).

Description. Life form: lichenized fungus.

[Modified from Lumbsch et al. 2011] Thallus foliose, up to 6–8(–10) cm across, corticate above and below; lobes hollow, usually readily divisible into two morphologically distinct lobe types: peripheral and central. Peripheral lobes short, usually about as broad as long, nearly or quite contiguous, usually flaring outward to the (rounded) tips, tending to wrap around the supporting branch, broadest ones 2–3(–4) mm wide, sometimes with small subapical perforations, these usually over the upper surface, but sometimes also at the lobe tip. Central lobes sparse to numerous, separate, more or less elongate, at least partly ascending, branching at first isotomic dichotomous, but later predominantly anisotomic, terminating at least in part in rather pointed tips, broadest ones 1.5–2.5 mm wide, occasionally with small lateral or axillary perforations (check near margin of lower surface). Upper surface whitish to pale pastel green, rather dull, becoming brownish where exposed, without black mottling, more or less rugose throughout, often becoming cerebriform toward thallus centre. Medullary ceiling white
(except weakly brown near ruptures in lower surface). Lower surface black; thin, easily torn, sharply wrinkled or folded, without rhizines. Soredia and isidia absent. Photobiont trebouxioid. Apothecia laminal, sparse to more often numerous, stalked, the stalks pale, often scabrid, the excipulum not much expanded (except sometimes expanded in age), often incurled at the rim; disk brown, the largest ones (2–)3–6(–8) mm across, deeply cup-shaped, the outer portions usually vertically oriented; ascospores ellipsoid, averaging (6.8–)8.0(–9.0) × (4.8–)5.7(–7.0) µm, L/W ratio (1.11–)1.41(–1.67); pycnidia copious over the upper surface forming tiny black dots; conidia (6.5–)6.9(–8.0) × 1 µm.

Secondary chemistry (TLC): atranorin, physodic acid (major, constant), unknown 7 (present, occasional); cortex K+ yellow, medulla KC+ abruptly pink.

Distribution and habitat: Currently known only from western intermontane North America, especially eastern Washington, north and central Idaho, western Montana, rarely north to southern intermontane British Columbia. Most specimens seen were collected from the branches of Pinus ponderosa, with occasional material also from Abies lasiocarpa, Artemisia tridentata, Pinus albicaulis and Pseudotsuga menziesii. Usually restricted in well-illuminated sites. This is the most frequently encountered Hypogymnia in some portions of eastern Washington and adjacent Idaho, sometimes a dominant macrolichen of conifer branches in
open, dry forests.