Leucopaxillus gentianeus
Description
Leucopaxillus gentianeus (syn. Leucopaxillus amarus) is a bitter-tasting, inedible mushroom. The bitter taste is caused by a triterpene called cucurbitacin B. The species was first described in 1873 as Clitocybe gentianea by French mycologist Lucien Quélet. František Kotlaba transferred it to Leucopaxillus in 1966.
The mycelial mat formed by the vegetative body of the fungus is particularly well developed and easy to observe when the mushrooms are collected. This characteristic, along with the dry cap, white gills that do not develop red spots in age, and very bitter taste distinguish L. gentianeus from the brown-capped tricholomas.
Common names: Bitter False Funnelcap, Bitter Brown Leucopaxillus, Bittermusseron (Swedish).
Mushroom Identification
Cap
The cap 5-11 cm broad, convex, expanding to plano-convex, sometimes with a broad umbo; margin at first incurved, becoming decurved, obscurely to conspicuously striate; surface smooth, dry, dull, reddish-brown to cinnamon brown, the margin lighter; flesh thick, white; taste bitter, odor usually unpleasant.
Lamellae
Gills close, adnate to notched, sometimes slightly decurrent, narrow, white, becoming cream.
Stipe
Stipe 4-8 cm tall, 1-2.5 cm thick, equal or tapering to an enlarged base; surface white, smooth, sometimes developing brownish stains at the base, the latter embedded in a layer of dense, white mycelium; veil absent.
Spores
Spores 4.5-6 x 3.5-5 µm, nearly round, warted, ornamentation amyloid; spore print white.
Habitat
Forming rings and arcs under conifers, e.g. coast redwood, Monterey pine, and Monterey cypress; less common with hardwoods; fruiting from late fall to mid-winter.
Flesh
White; not changing when sliced.
Odor and Taste
Odor strongly mealy; taste bitter.
Chemical Reactions
KOH olive on pigmented cap surfaces; negative on faded caps.
Spore Print
White.
Microscopic Features
Spores 4–6 x 3–4 µm; broadly ellipsoid to nearly subglobose; spiny with spines less than 0.5 µm high; amyloid. Lamellar trama more or less parallel. Basidia 4-sterigmate. Pleurocystidia not found. Cheilocystidia 20–40 x 1–4 µm; cylindric-flexuous, fusiform, or slightly irregular; hyaline and smooth in KOH. Pileipellis a cutis; yellowish or brown in KOH; elements 5–7.5 µm wide, clamped, smooth or encrusted with brown pigment; terminal cells cylindric with rounded apices.
Medicinal Properties
Antibiotic activity
The mycelia and cultural filtrates of the bitter false funnelcap were tested for antibiotic activity against Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, Salmonella typhimurium and Candida albicans. L. gentianeus was only active against Bacillus cereus (Colletto, 1995), but in a later study also against B. cereus (Colletto and Giardino, 1996).
Antitumor effects
The in vitro growth inhibitory effects of the cucurbitane triterpenoids mentioned above was tested for their effects on the proliferation of four different human tumor cell lines (A549, CAKI-1, HepG2, MCF-7), using a 1-day MTT assay. Only cucurbitacin B was highly active against all lines, with IC50 values of 46.6, 7.1, 0.76 and 0.78 µM, respectively (Clericuzio et al., 2004).
Photo sources:
Photo 1 - Author: Ron Pastorino (Ronpast) (CC BY-SA 3.0)
Photo 2 - Author: Jocelyn Gwynn (joceyg) (CC BY-SA 3.0)
Photo 3 - Author: Jerzy Opioła (CC BY-SA 4.0)
