Habitat and Range
Armillaria sinapina has 1) a pale to dark brown cap with reddish tinges, 2) a mustard yellow veil [but see Volk comment below], 3) brown scales, (as opposed to dark to very dark brown cap densely covered with dark scales), 4) fibrous, thin, appressed annulus that is mustard to golden yellow (as opposed to thick, membranous, white and brown), 5) club-shaped stem covered with mustard yellow remnants of veil (as opposed to cylindric, broad and yellow at apex), and 6) cylindrical rhizomorphs with monopodial branching (as opposed to belt-shaped with dichotomous branching), (Berube). It is difficult to distinguish between A. ostoyae and A. sinapina in a colonized stump because both produce white mycelial fans in the bark and cambial zone, however, A. sinapina produces an extensive network of monopodially-branched rhizomorphs while A. ostoyae produces small amounts of dichotomously branched ones; also the fruiting bodies of A. sinapina are usually darker in color, with darker cap scales, smaller, and more numerous than those of A. ostoyae, (Allen). The golden yellow color of the universal veil has not been observed on western specimens of A. sinapina, (Volk). A. sinapina differs only slightly in appearance, with a cobwebby veil and slightly smaller cap scales, growing singly or in clusters of only a few individuals, (Trudell). Armillaria gallica has white cobwebby veil, pinkish brown color, bulbous-based stem, and occurs singly or in groups rather than clusters, on or near logs, stumps, or bases of hardwoods such as willow, (Trudell). Armillaria nabsnona 1) has a more orange coloration when fresh, 2) lacks scales on the cap (but small black hairs may be found), 3) has a narrower stem in comparison to the size of the cap, the stem being darker, especially when dried, 4) fruits with hardwoods red alder, usually singly or in groups rather than clusters, and 5) microscopically has a distinctive pattern of branching of the basidia. Armillaria mellea [not recorded from Pacific Northwest] can occur in the same habitat, but A. ostoyae distinguished by its nonviscid, predominantly brown to dark brown cap covered by numerous dark scales, the brownish ring (annulus) on the stem, and the clamp connections at the base of the basidia, (Berube).typically in large clusters but sometimes single on or about stumps or trees, July to November, (Bessette), in BC found from 49 degrees latitude to 53 degrees primarily on conifers, but hardwoods within disease centers in conifer stands were frequently attacked and killed, (Morrison), on the Olympic peninsula in Washington, almost exclusively on conifers, especially Tsuga heterophylla (Western Hemlock), but also Pseudotsuga menziesii (Douglas-fir) and Picea sitchensis (Sitka spruce), (Banik), singly but most commonly in large fasciculate groups on decaying wood debris, dead stumps, dead trees, dead roots, declining trees, and healthy roots, hosts include Acer (maple), Betula (birch), and Quercus (oak), (Berube), a serious problem in Malus and Prunus orchards in Michigan (Burdsall), usually in clusters, mostly on conifers, but also on hardwoods and shrubs such as Salix (willow) and Rubus spectabilis (salmonberry), (Trudell), summer, fall