BOLETUS MIRABILIS Murrill, Mycologia 4:217. 1912
Ceriomyces mirabilis Murrill, Mycologia 4:98. 1912.
Xerocomus mirabilis (Murrill) Singer, Rev. Mycol. 5:6. 1940.
Boletellus mirabilis (Murrill) Singer, Farlowia 2:129. 1945.
Illustrations: See Microfiche No. 13
Smith, A. H., Mushrooms in Their Natural Habitats, Reel V.
Smith, A. H., The Mushroom Hunter's Field Guide, p. 101.
Smith, A. H., and H. D. Thiers, The Boletes of Michigan, pls. 93, 94.
Snell, W. H., and E. A. Dick, The Boleti of Northeastern North America, pl. 3.

Pileus 7-15 cm broad, convex to obtusely convex when young, becoming broadly convex to plano-convex when mature; surface moist to lubricous when young, dry when older, somewhat appressed fibrillose-scaly to rough-tomentose when young, becoming conspicuously fibrillose-scaly and often squarrose-scaly with age, sometimes appearing granular-scaly to somewhat areolate or rimose scaly; color dark reddish brown ("carob brown" to "bay" to "chocolate") unchanging during all stages of development, occasionally the scales slightly darker in color, pallid flesh rarely showing between the scales; margin sterile, often appendiculate, occasionally inrolled to incurved, becoming decurved with age. Context 1-2 cm thick, white to yellow ("naphthalene yellow" to "ivory yellow") often tinged vinaceous near the cuticle, frequently with numerous areas staining flesh-colored ("testaceous") when older, rarely changing to blue in irregular areas. Taste acid or mild; odor not distinctive.

Tubes 1-2.5 cm long, deeply and frequently broadly depressed around the stipe, yellow ("oil yellow" to "sulphur yellow") when young, changing to olive yellow ("olive lake") with age, unchanging when bruised; pores 1-2 mm broad, round to angular, concolorous with tubes, unchanging or becoming deeper yellow when bruised.

Stipe 8-15 cm long, 1-3 cm thick at the apex, clavate (stature of B. russellii), up to 5 cm thick at base, solid, with yellow mycelium at the base; surface moist to dry, glabrous, but typically shaggy reticulate at the apex, becoming smooth to uneven or ridged or shallowly pitted toward the base sometimes becoming roughened and split with age; color dark brown ("carob brown" to "chocolate" to "bay") with occasional streaks of ivory or beige or brown. Context pale vinaceous ("avellaneous" to "testaceous"), sometimes appearing yellow and typically becoming yellow when dry.

Spore print olive brown. Spores 18-22 X 7-9 µm, ochraceous in KOH, dark brown in Melzer's, subfusoid to subellipsoid, smooth, thick-walled.

Basidia 31-36 X 7-11 µm, clavate, hyaline, four-spored. Hymenial cystidia 60-90 X 10-18 µm, scattered to numerous, hyaline, thin-walled, fusoid-ventricose with obtuse to elongated apices.

Tube trama gelatinous, hyaline, divergent from a central strand. Pileus trama homogeneous, interwoven. Pileus cuticle when young differentiated as a closely packed trichodermium, 120-160 µm thick, hyphae 10-15 µm wide, more or less cylindric, noticeably septate, terminal cells typically slightly tapered, pale yellow in KOH, reddish brown in Melzer's, with age unchanging or collapsing and becoming somewhat disarticulated. Stipe cuticle fertile in apical portion with scattered to somewhat clustered, large, thin-walled, hyaline, fusoid-ventricose caulocystidia, 50-80 X 12-18 µm, becoming loosely and irregularly interwoven toward the base. Clamp connections absent.

Chemical reactions NH4OH-context very pale green; HNO3-context pale vinaceous, cuticle pink.

Habit, habitat, and distribution Solitary to scattered in soil in coastal forests. Known only from the northern coastal counties. Occasionally found on rotten coastal hemlock logs or stumps. It never appears in great abundance in northern California, perhaps the southernmost extension of its range. In Oregon and Washington it is common, and typically found associated with hemlock logs and stumps.

Material studied Del Norte County: Thiers 14315, 17717, 21339, 21565. Humboldt County: Thiers 14503, 21382. Mendocino County: Thiers 10584, 10673, 14154, 14604, 21770, 24197, 27000; Wennekens 42.

Observations This is one of the most stately and easily recognized boletes in California. The uniform dark brown color, noticeably scaly pileus, and the long stipe are highly distinctive. In an earlier paper this species was considered to belong to the genus Boletellus because of its stature, general appearance, and because some workers had reported the spores as being obscurely punctate or roughened. Repeated examinations of California material have failed to reveal any roughened spores and since, in modern concepts Boletellus is restricted to species having such spores, it has been placed back in Boletus. Additional features showing affinity with Boletus are found in the divergent tube trama, yellow tubes, and dry to moist pileus surface.

This bolete is considered edible and choice.

Online edition addendum

Other Descriptions and Photos: The Fungi of California

The Boletes of California
Copyright © 1975 by Dr. Harry D. Thiers
Additional content for the online edition © 1998 by Michael Wood, Fred Stevens, & Michael Boom
A MykoWeb Page