Tyromyces chioneus: The Ultimate Mushroom Guide
About The Tyromyces chioneus Mushroom
Tyromyces chioneus is an inedible species of polypore fungus with a white cap and pore surface, combined with its soggy texture and lack of interesting microscopic details. A widely distributed fungus, it has a circumpolar distribution, in temperate boreal pine forests, of Asia, Europe, and North America, which causes white rot in dead hardwood trees, especially birch.
When fresh, this polypore feels soft and watery. Droplets of water are easily squeezed out of it. The polypore has a fragrant odor when fresh.
Other names: White Cheese Polypore.
Tyromyces chioneus Identification
Saprobic on the deadwood of hardwoods, especially birch; causing a white rot; annual; growing alone or with two or three other fruiting bodies; summer and fall; fairly widely distributed from the Great Plains to the Maritime provinces but absent in the southeastern United States - also reported in the Pacific Northwest and northern California.
Up to 12 cm across and 8 cm deep; convex; semicircular to kidney-shaped; very finely velvety at first, becoming bald and, in old age, developing a crusty surface that becomes wrinkled or shriveled; white to off-white or, in age, yellowish to brownish; soft.
White, becoming yellowish in old age or when dried out; not bruising appreciably; with 3-5 circular to angular pores per mm; tubes to 8 mm deep.
White; soft and watery when fresh.
Odor and Taste
Odor fragrant when fresh; taste not distinctive, or slightly bitter.
KOH negative on cap surface and flesh.
Spores 4-5 x 1.5-2 µ; smooth; cylindric to slightly allantoid; hyaline in KOH; inamyloid. Cystidia are absent, but fusoid cystidioles are present. Hyphal system dimitic.
Tyromyces chioneus Look-Alikes
Has a cap surface that is white to pale gray, and strigose to hispid, spores are 2.5-3.0 x 2.0-2.5 microns, and skeletal hyphae are lacking, whereas T. chioneus has a cap surface that is white to dark gray, and finely tomentose to bald, spores are 4-5 x 1.5-2.0 microns, and there are skeletal hyphae in the trama.
Calcipostia guttulata and Postia stiptica
Similar in appearance and microscopically, but those species have a bitter taste, fresh or dried, and they are not restricted to hardwoods.
Has a rough cap that usually has small, back dots on the surface, and C. guttulata has a weakly zonate cap with saucer-shaped depressions 0.1-0.3cm in diameter, an exudation of drops of liquid on most fresh fruitbodies, and a faint greenish cast to the pore surface.
Has slightly narrower spores (4.5-6 x 1-1.5 microns), a monomitic hyphal system without the characteristic branched generative hyphae, and produces a brown rot.
May lack its typical mouse-gray cap surface, in which case it is differentiated by its narrower (1.0-1.5 microns), allantoid spores.
Tyromyces chioneus Taxonomy
The species was first described as Polyporus chioneus by Elias Fries in 1815. It was transferred to the genus Tyromyces by Petter Karsten in 1881. Tyromyces chioneus is the type species of Tyromyces. The specific epithet chioneus means "snow", referring to its white color.
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