Strobilurus occidentalis is very closely related to a second western North American species, S. wyomingensis, that also produces basidiomes on cone of Picea (FIG. 1; SUPPLEMENTARY FIG. 1), as well as an undescribed species that associates with Pinus cones from Macedonia. Indeed, S. occidenatalis is a paraphy- letic species from which the other two are derived. This could support Redhead’s conclusion that “S. wyomin- gensis is a variety of S. occidentalis.” Morphologically, the pilei and basidiospores of S. wyomingensis are usually larger than those of S. occidentalis (Arenberg 1941; Smith 1947; Wells and Kempton 1971; Redhead 1980, 1989). The former has been recorded in subalpine habitats of Wyoming, Idaho, and Colorado) (Redhead 1989), whereas S. occidentalis occurs at lower elevations in the Pacific Northwest.
Basidiospores [145/6/6] 4–5.5(–6.5) × (2–)2.5–3(–4) μm, [Q = (1.33–)1.50–2.00(–2.90), Qm = 1.71 ± 0.23], ellipsoid, elongate to lacrymoid, hyaline, thin-walled, smooth, inamyloid. Pleurocystidia 30–60 × 8–14 μm, fusoid, thick-walled (ca. 1 μm thick), occasionally thin- walled; apices usually subacute, slightly thick-walled.
Habitat: Autumn, on cones of Picea, western North America.