Major Groups > Polypores > Stemmed, Pale-Fleshed > Osteina obducta


Osteina obducta

[ Basidiomycota > Polyporales > Fomitopsidaceae > Osteina . . . ]

by Michael Kuo

This curious polypore features a fairly substantial stem, laterally attached to the deadwood of conifers. The cap is smooth and whitish to grayish or pale brown, and the pore surface is white, composed of small, angular pores. Osteina obducta appears to be fairly widespread in North America, judging from the online records of major herbaria, but far more common in western and northern ecosystems.

One of the most distinctive features of Osteina obducta cannot be determined until it is dried for study; its firm but pliant flesh becomes extremely hard—we're talking, like, hard as a rock. I was sure that the collection sent to me and featured here had been baked in a kiln for a few days; I had to rehydrate a small section for hours before I could work with it. It wasn't until I began consulting polypore literature that I discovered that Osteina obducta was supposed to be like that: "very rigid and brittle when dry" (Berkeley, 1845, in the first description of the fungus), "the context dries hard" (Overholts, 1953); "hard and horny when dry" (Gilbertson & Ryvarden, 1987) (let it go).

Under the microscope Osteina obducta is not much fun to work with. Its spores are tiny and colorless, making them hard to find—and it has two kinds of hyphae, one of which is partially gelatinized and hard to isolate, while the others are so tightly wound together that they, too, are hard to see individually.

Polyporus zelleri, Polyporus osseus, and Oligoporus obductus are synonyms.

Thanks to Lisa McLennan for collecting, documenting, and preserving Osteina obducta for study; her collection is deposited in The Herbarium of Michael Kuo.


Ecology: Saprobic on the deadwood of conifers (and rarely reported on the deadwood of hardwoods); causing a brown rot; growing alone or gregariously, usually in overlapping clusters; annual; fairly widely distributed in North America but more commonly reported from montane and northern areas. Also known from central Europe and Japan. The illustrated and described collection is from Colorado.

Cap: 4–10 cm across; broadly convex; more or less semicircular to fan-shaped; the margin becoming widely scalloped; dry; bald; whitish, grayish, or pale brown (usually becoming brown when dried for study).

Pore Surface: Running down the stem; whitish to dull yellowish; not bruising; 3–5 angular pores per mm; tubes 2–3 mm deep.

Stem: 2–5 cm long; 1.5–2 cm thick; tapered to base; bald; whitish to grayish or brownish; not bruising.

Flesh: Thick and pliant when fresh; white; not changing on exposure; when dried becoming extremely hard.

Microscopic Features: Spores 3–5 x 1–2 µm; cylindric, with apicular end subacute; smooth; hyaline in KOH; inamyloid. Basidia 25–30 x 3–5 µm; clavate; 4-sterigmate. Cystidia not found. Setae not found. Hymenial trama hyphae 2–4 µm wide; thin-walled; smooth; hyaline in KOH; tightly wound together. Contextual hyphae 5–10+ wide; walls 2–5 thick; smooth; hyaline in KOH; with large, looping clamp connectionsOs; partially gelatinized and difficult to isolate.

REFERENCES: (Berkeley, 1845) Donk, 1966. (Murrill, 1915; Overholts, 1953; Smith, 1975; Breitenbach & Kränzlin, 1986; Gilbertson & Ryvarden, 1987; Phillips, 1991/2005; Lincoff, 1992; Cui et al., 2014.) Herb. Kuo 08011801.

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Osteina obducta

Osteina obducta

Osteina obducta

Osteina obducta
Hymenial hyphae

Osteina obducta
Contextual hyphae

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Kuo, M. (2019, September). Osteina obducta. Retrieved from the MushroomExpert.Com Web site: