Cap 15-50 mm broad, campanulate to plano-umbonate, umbo covered with tiny dark brown tufts, with scattered squamules towards the margin, dry, disc brown, margin pale creamy brown to beige. Gills adnate, subdistant, broad, grayish orange. Stem 25-40 x 4-5 mm, clavate, dry, pubescent, pale brown; partial Viel forming a cottony, white annulus near Stem apex when young, remaining as a white cottony ring or fibrillose zone in age. SporeDeposit white. Edibility: unknown.
This Hawaiian Armillaria is found growing solitary or in scattered clusters on fallen tree ferns, or in large clusters on logs and decaying ohi‘a trees. It is closest to A. ostoyae from north temperate regions, but we have not yet confirmed this diagnosis with mating studies or DNA analysis. Armillarin nabsnonia has been reported recently from Hawai'i as growing on healthy koa and ohi‘a, and our material from native rainforests may represent that species. Is: HA.