|Major Groups > Boletes > Leccinum > Leccinum subglabripes|
Leccinum subglabripes (Peck) Singer, 1945
= Boletus flavipes Peck (1886) non Berkeley (1854)
by Michael Kuo
Leccinum subglabripes grows under oaks in the southern part of its range, and under birch or aspen in its northern range. Its stem is fairly long and slender, and its proportions are more Leccinum-like than Boletus-like. The yellow stem surface is adorned with the scabers that typify the genus Leccinum, but in Leccinum subglabripes the scabers are inconspicuous and are usually best observed with a hand lens; Peck's species name, Latin for "nearly smooth-stemmed," is quite appropriate--as is his comment that "the branny particles on the stem are pale and easily overlooked" (1889, p. 112). The flesh is yellow, and it does not change color dramatically when sliced (though it may turn slightly reddish and/or pale blue in a few spots). The cap is cinnamon brown to orangish brown, and its surface is bald, sometimes developing a wrinkled or even corrugated appearance. The pileipellis is a clearly defined epithelium.
In the tradition of Smith & Thiers (1968, 1971) this mushroom is "Boletus subglabripes," placed outside Leccinum because its inconspicuous scabers do not darken to brown or black. It is a difficult mushroom to characterize, and it certainly should be included in identification keys for Boletus. However, molecular evidence supports the concept of Singer (1945, 1947, 1986), and the species belongs in Leccinum.
Ecology: Mycorrhizal with oaks, birch, and aspen (possibly also with beech; rarely and probably erroneously reported with conifers); appearing in diverse ecosystems; growing alone, scattered, or gregariously in (June,) July, August, and September. My collections have been made under Populus grandidentata, Populus tremuloides, and various species of Quercus in July and August.
Distribution: Difficult to state with certainty, but possibly widely distributed in boreal and northern forests featuring aspen and birch, and widely distributed in eastern and southeastern oak forests. Figure 1 represents the distribution of Leccinum subglabripes based on 228 online herbarium collection locations (everything but Idaho; I have excluded one MICH collection from downtown San Diego under conifers), collections in my herbarium, and on Smith's 1975 Field Guide to Western Mushrooms (1975), which describes and illustrates Boletus subglabripes from Bonner County, Idaho. Scates (1980) cites a Thiers communication to Norvell that Leccinum subglabripes occurs in Washington. My collections have been made in Minnesota, northern Michigan, and Illinois.
Macromorphology: Pileus (3-) 4-10 (-15) cm; convex becoming broadly convex or nearly plane; surface dry or slightly tacky, glabrous; smooth, rugulose, rugose, or corrugated-pitted; cinnamon brown to reddish brown or yellow-brown; occasionally with a very tiny sterile margin. Context yellow mixed with darker, lemon yellow areas; rarely whitish in places; soft; sometimes developing reddish areas with age, especially around larval tunnels; unchanging when sliced, or bluing faintly (especially over the tubes); often invaded in the stipe by larvae. Tubes to 15 mm long; yellow, becoming greenish yellow or olive; pore surface similarly colored, not bruising, depressed at the stipe; 1-3 round to angular pores per mm. Stipe 5-11 cm long; up to 2.5 cm wide; at maturity more or less equal, or tapering slightly to apex or base; bright yellow apically, bright to pale yellow below; often becoming reddish tinged in the middle or basally; very finely scabrous with tiny yellow scabers that sometimes become slightly reddish; basal mycelium whitish. Odor not distinctive; taste mild or slightly acidic. Exsiccata with brown to orangish brown pilei, bright ochraceous to orangish brown pore surfaces, and bright yellow stipe surfaces adorned with concolorous to brownish or cinnamon brown scabers. Spore print olive.
Chemical reactions: Iron salts negative to grayish or olive on context; KOH negative to orangish or reddish on pileus surface, dirty orangish on context; ammonia negative on pileus surface, negative to dirty greenish on context.
Micromorphology: Basidiospores subfusoid; inamyloid; hyaline or greenish ochraceous in KOH; smooth; 10-20 x 3-5 µ. Basidia clavate; four-sterigmate; up to 34 x 12.5 µ. Hymenial cystidia fusoid-ventricose to fusoid; up to 54 x 15 µ; hyaline to ochraceous in KOH; numerous near the tube mouths. Pileipellis (Figure 2) a tightly packed trichoderm with terminal elements inflated to
Molecular Data: Two partial sequences have been deposited in GenBank: AY139688 (partial 28S ribosomal RNA, deposited by Binder & Besl without a voucher citation), aligned by Binder & Besl (2000), Binder & Hibbett (2004) and by den Bakker & Noordeloos (2005); and AD001568 (partial large subunit ribosomal RNA, deposited by T. D. Bruns and collaborators without a voucher citation), aligned by Bruns and collaborators (1998). The Binder & Hibbet and den Bakker & Noordeloos alignments of AY139688 are quite similar, placing it in a clade with specimens identified as Boletus longicurvipes and Boletus rubropunctus. The alignment by Bruns and collaborators of AD001568 places it in a poorly defined clade with specimens identified as Boletus flaviporus and Boletus smithii, near but not clearly sister to a clade containing specimens identified as Leccinum species, Chamonixia ambigua, and Strobilomyces floccopus. Currently, molecular data for Leccinum subglabripes approaches being useless, in my opinion; see "Comments" for further discussion and for suggestions for further molecular research.
Anyone who has spent much time trying to identify eastern North American boletes knows that the name "Boletus subglabripes" is a potential identification dumping ground; it can often be used as a replacement for "I'm not spending any more time with this mushroom," or "close enough" . . . even by professional mycologists. There are over 200 collections labeled Boletus or Leccinum subglabripes in online herbaria, but I doubt they are all identified correctly (H. E. Bigelow 6893 in NY, for example, is clearly a Suillus, despite being collected and identified by such a prominent mycologist). While a certain amount of caution is required when studying any taxon with herbarium specimens, caution is especially required in the case of Leccinum subglabripes.
Singer (1947) noted minor but apparently consistent morphological differences between "northern collections" (he cited material from New Hampshire, Massachusetts, New York, and Ontario) in "frondose woods under black or yellow birch and also under oak," and Florida collections that were made "[u]nder oaks in high and mesophytic hammocks." Northern collections, according to Singer, were more prone to reddish stains and discolorations on the stem surface and in the context, but he conceded that his "experience in spite of the numerous carpophores examined is too limited to evaluate the constancy of these different shades." Examination of the 200 collection records in online herbaria reveals that northern collectors are more likely to mention birch or aspen, while southern collectors are more likely to mention oaks. This is to be expected, of course, given the ranges of the trees--but since European researchers (den Bakker and collaborators, 2004b) found only one species of Leccinum (the European species Leccinum aurantiacum, apparently not known from North America) to demonstrate the kind of mycorrhizal generalism that would be required to associate with birch, aspen, and oak, the possibility that there are two or more cryptic, host-specific species hiding within Leccinum subglabripes is raised.
Molecular results for Leccinum subglabripes cannot be taken very seriously at the present. We have a partial sequence of one gene from a mushroom identified by someone as "Boletus subglabripes," collected somewhere, possibly (or possibly not) saved in a public herbarium . . . in short, we have string of the letters A, C, G, and T (hopefully copied and pasted without errors) in an online database. To be clear, I am not questioning whether the placement of Leccinum subglabripes in a clade with Leccinum longicurvipes, nested within the Leccinum clade, is accurate; Singer thought this in 1947 on the basis of morphology, after all, and I think the odds are high that "AY139688" was identified correctly, that a few e-mails would turn up a voucher somewhere for further research, and that a molecular study of many carefully documented Leccinum subglabripes specimens would confirm, at least in part, the present results.
But further study is definitely required in order to approach anything resembling scientific understanding, especially in the case of this taxon, since its mycorrhizal associations appear to be diverse and suggest the possibility of cryptic species. What is needed now is a study in which dozens of well documented specimens identified as Boletus and Leccinum subglabripes, from various ecosystems, are sampled. For starters, Roy Halling's collections in the New York Botanical Garden herbarium (7054, under oaks; 6572, under birch and aspen; 2989, under birch; 4495, under oak and beech; 4570, under oak; and 7795, under oaks in Costa Rica) are ecologically and morphologically diverse, well photographed, and recent enough that normal protocols can probably extract DNA.
References and Material Studied:
Collections Examined: MINNESOTA: Kuo 07180209 (Cass County). MICHIGAN: Kuo 07199401, 07219400, 07279400, 09039400 (all Emmet County). ILLINOIS: Kuo 06130209, 08160504, 08240506 (all Coles County). IOWA: 08180901 (Decatur County; S. Brown).
Collection Notes Examined: Bigelow 10436 (Maine, 1962; NY).
Field Guides and Online Treatments: Smith, 1975; Scates, 1980; Smith, Smith & Weber, 1981; Phillips, 1991/2005; Barron, 1999; Bessette, Roody & Bessette, 2000; McNeil, 2006; Kuo, 2007; Phillips, 2007.
Technical References: Peck, 1889; Coker & Beers, 1943; Singer, 1947; Smith & Thiers, 1968; Snell & Dick, 1970; Smith & Thiers, 1971; Grund & Harrison, 1976; Both, 1993; 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 subglabripes. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/leccinum_subglabripes.html