Major Groups > Boletes > Leccinum > Leccinum pseudoscabrum


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Leccinum pseudoscabrum (Kallenbach) Sutara, 1989

= Boletus pseudoscaber Kallenbach, 1935
= Leccinum carpini (R. Schulz) D. Reid, 1965
and previous combinations
= Leccinum griseum sensu Snell & Dick (1970), Smith & Thiers (1971)

by Michael Kuo


Leccinum pseudoscabrum, better known as "Leccinum carpini," is mycorrhizal with Carpinus caroliniana, commonly known as blue beech or hornbeam. It has tiny, dot-like scabers that are blackish brown or black by maturity, and like other species in section Luteoscabra it lacks overhanging marginal flaps and has an "epithelium"-like pileipellis. The cap is grayish brown, and often becomes cracked with age. Leccinum pseudoscabrum is a well defined species in Europe; I am treating "Leccinum griseum" in the sense of several North American authors as a probable synonym. For a description of the European species, see den Bakker & Noordeloos (2005, 2006). The description below is based on North American "Leccinum griseum" collections. Differences between European and North American material are noted in the comments.

Technical Description:

Ecology: Probably mycorrhizal with Carpinus caroliniana, but generally reported as growing under oaks (see comments below); often found in semi-urban environments, and in hardwood forests; growing alone or gregariously; (June,) July, August, and September.

Distribution: Probably throughout the range of the mycorrhizal host, in eastern and southeastern North America and in the tropical cloud forests of Mexico. Figure 1 represents the ranges of Carpinus caroliniana and "Leccinum griseum."

Macromorphology: Pileus 3-12 cm; convex becoming broadly convex; surface dry, glabrous or nearly so; often rugose or rugulose; sometimes becoming areolate with age; yellowish brown, reddish brown, or, most commonly, gray-brown to dark brown or nearly black, sometimes with olive or greenish tinges; without a substantial sterile margin. Context whitish; soon gray to blackish when sliced and exposed to air, sometimes after a pinkish to purplish stage. Tubes to 20 mm long; whitish to grayish at first, developing yellowish and/or olive shades; pore surface whitish to pale grayish, developing yellowish or olive overtones with age, bruising brownish to yellowish or olive, depressed at the stipe; 1-2 more or less round pores per mm. Stipe 4-13 cm long; 6-14 mm wide at apex; slightly tapered to apex; whitish to grayish; densely scabrous with fine, brown to brownish black scabers; sometimes bruising or discoloring greenish near the base; basal mycelium white. Odor and taste not distinctive. Spore print cinnamon brown to brown. Exsiccata (Figure 3) with medium grayish brown pilei, frequently conspicuously areolate with pale context exposed; hymenia brown with orangish or reddish tinges; stipe surfaces tan to off-white near the base, covered with very fine medium brown to blackish brown scabers.

Chemical reactions: Not documented.

Micromorphology: Basidiospores (Figure 5) subfusoid; inamyloid; smooth; 10-28 x 4-7 µ. Basidia clavate; four-sterigmate; up to 32 x 12 µ. Hymenial cystidia (Figure 4) fusoid-ventricose to fusoid; up to 42 x 14 µ; hyaline to ochraceous in KOH; scattered. Pileipellis (Figure 4) a trichoderm with inflated, subglobose terminal elements measuring up to 35 µ wide. Caulocystidia (Figure 4, Figure 6) in bundles with caulobasidia; mostly fusoid-ventricose to lageniform but occasionally mucronate or fusoid; up to 50 x 15 µ but generally shorter; hyaline to yellowish or brownish in KOH.

Molecular Data: Three partial sequences, all probably representing European material, have been deposited in GenBank with the label Leccinum carpini (no deposits for Leccinum griseum): AY538785 (Gapdh, deposited by H. C. den Bakker and collaborators with a voucher of "HdB065-L"), which is a den Bakker collection in the Nationaal Herbarium Nederland at Leiden, aligned by den Bakker and collaborators (2004b); AF454588 (partial 18S, complete ITS1, 5.8S, and ITS2, partial 28S; deposited by H. C. den Bakker and collaborators without a voucher citation), aligned by den Bakker and collaborators (2004a); and AF139691 (partial 28S large subunit ribosomal RNA, deposited by Binder & Besl without a voucher citation), aligned by Binder & Besl (2000), Binder & Hibbet (2004), and den Bakker & Noordeloos (2005). The cited alignments are similar (though not identical), placing Leccinum carpini in clades with oak-associated taxa like Leccinum crocipodium and Leccinum albellum.


The description of the caulocystidia above, to my knowledge, is the first for North American material; it is based on my examination of AHS 15410 and AHS 84011, both from lower Michigan. Neither Smith, Thiers & Watling (1967) nor Smith & Thiers (1971) included data on caulocystidia.

Although my hypothesis in this treatment is that they may be the same, the differences between "Leccinum griseum" in the sense of Smith, Thiers & Watling (1967), Snell & Dick (1970), and Smith & Thiers (1971) and the European Leccinum pseudoscabrum (syn. Leccinum carpini) are not insignificant. First and foremost, the American taxon is not documented under Carpinus, though most records do not exclude the possibility once the tree's stature as an easy-to-miss understory tree is recalled (see Figure 2). Morphologically, the American taxon "differs from L. carpini in the flesh not turning vinaceous when sectioned and in the tubes showing no yellow flush when young" (Smith, Thiers & Watling, 1967). However, the contemporary concept of Leccinum pseudoscabrum does not necessarily exclude the non-yellowish tubes, which may be "yellowish to pinkish brown or greyish brown . . . with brownish tinge when old" (den Bakker & Noordeloos, 2005), and the absence of a purplish stage in the staining of the sliced context is probably not taxonomically important. A potentially more important difference lies in the scabers, which in American material are very fine and brown to dark brown, microscopically represented by caulocystidia that are yellowish to brownish in KOH.

Spore dimensions in North American material are apparently quite variable; Snell & Dick (1970) record a range of "10-20 (25) x (4) 5-7 (8) µ," and I found similar variation (16-28 x 5.5-7.5 µ) in AHS 15410.


Leccinum pseudoscabrum
Leccinum pseudoscabrum, Sweden
Note: Mushrooms were collected under Carpinus and repositioned for the photo.

Leccinum griseum
Leccinum griseum
Courtsey of the University of Michigan Press and Herbarium

Leccinum pseudoscabrum
Figure 1

Leccinum pseudoscabrum
Figure 2

Leccinum pseudoscabrum
Figure 3

Leccinum pseudoscabrum
Figure 4

Leccinum pseudoscabrum
Figure 5

Leccinum pseudoscabrum
Figure 6

References and Material Studied:

Collections Examined: MICHIGAN: AHS 15410 (Washtenaw County, 1967; MICH), AHS 84011 (Livingston County, 1972; MICH). CZECHOSLOVAKIA: Dermek 3 Oct. 1967 (MICH).

Online Herbarium Records Examined: NY: 6; MICH: 15; OSU: 0; TENN: 1; BPI: 1.

Field Guides and Online Treatments: Smith, Smith & Weber, 1981; Weber & Smith, 1985; Bessette, Roody & Bessette, 2000; Karasinski, 2004; den Bakker & Noordeloos, 2006; Miller & Miller, 2006; Snowarski, 2006.

Technical References: Smith & Thiers, 1967; Snell & Dick, 1970; Smith & Thiers, 1971; Both, 1993; Lannoy & Estades, 1995; den Bakker and collaborators, 2004; Binder & Hibbett, 2004; den Bakker & Noordeloos, 2005. Full citations for these works can be found here.

Cite this page as:

Kuo, M. (2007, May). Leccinum pseudoscabrum. Retrieved from the MushroomExpert.Com Web site:

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