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[ Basidiomycota > Russulales > Auriscalpiaceae > Lentinellus . . . ] Lentinellus ursinus by Michael Kuo, 27 August 2025 This Lentinellus species is sometimes called the "Bear Lentinellus," in a translation of its Latin name, ursinus—but what that wacky old Swede Elias Fries was thinking when he named the mushroom is beyond me. Nothing about Lentinellus ursinus strikes me as bear-like, except for the bear of a headache involved with identifying it. Like other species in the genus, Lentinellus ursinus grows on wood and features saw-toothed gills and a white spore print, along with spores that feature amyloid ornamentation. The species lacks a stem, which places it in the difficult-to-separate group of pleurotoid Lentinellus species—several of which, for reasons unknown, are named after mammals. One begins to wonder whether the mycological founders were studying mushrooms or Aesop's Fables. At any rate, in order to separate the bear (Lentinellus ursinus) from the fox (Lentinellus vulpinus) and the beaver (Lentinellus castoreus), your potential tactics range from 1) attempting to assess physical features visible to the naked eye, to 2) using a strong magnifying glass or a dissecting microscope to assess physical features in dried specimens and applying Melzer's reagent or Lugol's solution to their flesh, or 3) using a microscope to assess hyphal types in one of the most difficult and irritating exercises in mycological microscopy you are ever likely encounter. Tactic 1 is obviously the easiest, but unfortunately not very conclusive with this species group; you will need to move to Tactic 2, at a minimum, to make a confident identification. For those who lack access to a magnifying glass, the ability to dry specimens, and Lugol's or Melzer's, here are the putative differences in macromorphological features available for attempting Tactic 1: ursinus and vulpinus tend to be larger, at maturity, than castoreus, and castoreus tends to feature a patch of brown velvety material that starts near the point of attachment to the wood and grows toward the margin as the mushroom matures (however, there are plenty of small bears and foxes, and the growing velvet patch can appear on all three species). Separating ursinus from vulpinus with Tactic 1 is especially difficult. Lentinellus vulpinus is more likely to become radially wrinkled and ridged with development, and it is more likely to feature brown-staining gills and flesh; additionally it is often paler than ursinus—but these "differences" are not clear cut, and often overlap. Tactic 2, if you are able to employ it, is your best bet. Lentinellus ursinus features a thin black line dividing the cap surface from the flesh, best observed with moderate magnification and dried specimens. Additionally, a drop of Melzer's reagent on the dried flesh produces an instant, strongly amyloid, color change to black. These two features reliably separate ursinus from vulpinus, which has inamyloid flesh and lacks the black line, and from castoreus, which may or may not have the black line, but lacks the strong amyloid reaction. Lentinellus ursinus robustus is a form designated by Petersen (2004) that usually appears on the deadwood of conifers, rather than hardwoods, and features a strong, fruity odor. Description: Ecology: Saprobic; growing in groups or in shelf-like clusters on the wood of hardwoods (or conifers in form robustus); summer and fall; originally described from Sweden (Fries 1821); widespread in Europe and North America; present in eastern Asia. The illustrated and described collections are from Illinois, Michigan, and Ohio. Cap: 2–12 cm across; fan-shaped to kidney-shaped or roughly semicircular; broadly convex, becoming nearly flat; finely, radially appressed-fibrillose or densely velvety (usually more fuzzy toward the point of attachment and more bald toward the margin); when young brown, at least toward the point of attachment; becoming brown with a paler margin, or pale grayish brown—or, eventually, whitish or orangish white; sometimes hygrophanous; sometimes becoming ridged and nearly reticulate in old age. Gills: Radiating from the point of attachment; close or nearly crowded; the edges distinctively saw-toothed; short-gills frequent; whitish to pale brownish. Stem: Absent. Flesh: Thin; tough; whitish to faintly brownish; unchanging when sliced; separated from the cap surface by a thin black to blackish line, best observed with magnification (a magnifying glass or dissecting microscope) of a freshly sliced section from a dried specimen. Odor and Taste: Odor fragrant, or not distinctive; taste usually strongly acrid or peppery. Chemical Reactions: KOH negative on fresh cap surface, or black on the velvety areas of tomentose caps; dried flesh instantly black (strongly amyloid) with Melzer's reagent or Lugol's solution. Spore Print: White. Microscopic Features: Spores 3–4 x 2–3 µm; ellipsoid; sparsely, finely spiny (difficult to detect with light microscopy); amyloid. Basidia 18–20 x 3–4 µm; clavate; 4-sterigmate. Pleurocystidia 22–30 x 4–6 µm; fusiform, cylindric, or cylindric with a small mucro; smooth; thin-walled; yellowish to hyaline in KOH. Gloeoplerous hyphae usually abundant; 3–6 µm wide; golden in KOH; weakly amyloid, with granular contents, in Melzer's. Skeletal hyphae present in context (especially at the base of the context, just above the hymenium); 3–10 µm wide; thick-walled; gnarled; amyloid (dark purple). Clamp connections present. REFERENCES: (E. M. Fries, 1821) R. Kühner, 1926. (Kauffman, 1918; Miller & Stewart, 1971; Smith, Smith & Weber, 1981; Arora, 1986; Breitenbach & Kränzlin, 1991; Phillips, 1991/2005; Lincoff, 1992; Horn, Kay & Abel, 1993; Barron, 1999; Miller & Methven, 2000; Roody, 2003; Petersen & Hughes, 2004; McNeil, 2006; Miller & Miller, 2006; Binion et al., 2008; Boccardo et al., 2008; Buczacki et al., 2012; Kuo & Methven, 2014; Siegel & Schwarz, 2016; Woehrel & Light, 2017; Knudsen, 2018; Sturgeon, 2018; Læssøe & Petersen, 2019; MacKinnon & Luther, 2021; McKnight et al., 2021.) Herb. Kuo 07260401, 09140802, 09301102, 08191402, 10301503, 10191601, 06122501, 06242501. 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Cite this page as: Kuo, M. (2025, August). Lentinellus ursinus. Retrieved from the MushroomExpert.Com Web site: /lentinellus_ursinus.html |