About Melanoleuca yatesii Murrill
This gilled mushroom species was formerly known as Tricholoma yatesii; according to Index Fungorum and Mycobank, its current accepted scientific name is Melanoleuca yatesii Murrill. It strongly resembles Tricholoma equestre, but differs in that it forms mycorrhizal associations with Quercus (oak trees and shrubs), while T. equestre associates with Pinus (pines). This mushroom is primarily found in California, with only a small number of observations from Oregon and Washington. Currently, it is not possible to produce complete, definitive taxonomic coverage of the genus Tricholoma in North America, so this species and its close relatives remain relatively understudied by science and unfamiliar to the general public. William A. Murrill's original 1912 description of this species, then published as Melanoleuca yatesii, noted the following characteristics: the pileus (cap) is regular, convex, and solitary, reaching 5-8 cm broad. Its surface is smooth, glabrous, viscid, and sulfur-yellow, turning brownish at the center when drying; the margin matches the cap's color, is entire, and curves inward when drying. The context (flesh) is rather thin, and ranges from white to pale yellow. The lamellae (gills) are sinuate-adnexed, rather broad, ventricose, and not crowded; they appear pale yellow when fresh, and develop some discoloration when drying. Spores are ellipsoid, smooth, hyaline, and measure 5 by 3 μ. The stipe (stem) is equal in shape, shining, nearly glabrous, sulfur-yellow, and fades to almost white when dry; it is 6-10 cm long and 8-12 mm thick. The species is named for H. S. Yates, who collected the type specimen under introduced eucalyptus and endemic Monterey cypress in Berkeley, California.
