Tyromyces chioneus

What You Should Know

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 Mushroom Identification

1. Ecology

   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.

2. Cap

   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.

3. Pore Surface

   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.

4. Flesh

   White; soft and watery when fresh.

5. Odor and Taste

   Odor fragrant when fresh; taste not distinctive, or slightly bitter.

6. Chemical Reactions

   KOH negative on cap surface and flesh.

7. Spore Print

   White.

8. Microscopic Features

   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

1. Tyromyces galactinus

   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.

2. 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.

3. Postia stiptica

   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.

4. Postia tephroleuca

   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.

5. Postia tephroleuca

   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.

Sources:

Photo 1 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 2 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 3.0 Unported)