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Bolbitius titubans

[ Basidiomycetes > Agaricales > Bolbitiaceae > Bolbitius . . . ]

by Michael Kuo

This widespread and common mushroom is quite variable in its size and stature. Young specimens have a distinctive, yellow, egg-shaped cap--but the short-lived Bolbitius titubans soon begins to fade, becoming convex or broadly conical, and eventually more or less flat. Robust specimens are found on dung and in heavily fertilized soil, while flimsy specimens can be found in grassy areas with less nitrogen.

The not-so-variable features, which should probably be relied on for accurate identification, include:

  • A rusty brown or cinnamon brown (but not dark brown) spore print;
  • A slimy cap that is deeply lined by maturity;
  • The absence of a partial veil;
  • Gills that are pale at first but become rusty brown;
  • Smooth, elliptical spores that have a flattened end and a "pore";
  • The presence of brachybasidioles on the gills.

"Bolbitius vitellinus" was traditionally separated from Bolbitius titubans on the basis of its thicker flesh, less striate cap, and whiter stem--but mycologists have recently synonymized the two species; since titubans is the older name, it takes precedence.

Bolbitius expansus is a yellow-stemmed taxon with a grayish yellow cap that does not retain a yellowish center at maturity. Bolbitius variicolor (possibly the same as Bolbitius vitellinus var. olivaceus) has a "smoky olive" cap and a finely scaly yellow stem; the original description and illustration of this taxon can be found in the right-hand column. Various authors synonymize one or more of these taxa with Bolbitius titubans (or vice-versa). In the absence of clear ecological or molecular data to separate them, I am throwing them all into the mix and using the most widely known species name to represent the group. There could easily be several ecologically and genetically distinct species among these taxa, but I doubt we will be able to accurately identify them on the basis of stem color, minor differences in spore dimensions, and so on. Comprehensive, rigorous documentation of ecology, morphological variation, and genetic difference in hundreds of specimens from across the globe is required.


Ecology: Saprobic, growing alone, scattered, or gregariously on dung and in fertilized grass; summer and fall (and winter in warm climates); widely distributed in North America.

Cap: 1.5-5 cm; egg-shaped or nearly round when young, expanding to broadly bell-shaped or broadly convex, and eventually flat with a depressed central bump; fragile; slimy when fresh; yellow or greenish yellow (sometimes brownish or grayish), often fading to grayish or pale tan but (usually) retaining a yellowish center; smooth; usually strongly lined by maturity, often nearly all the way to the center. Specimens developing a pocketed or veined cap surface as the slime dries out are not infrequent. Young specimens sometimes display a felty, whitish cap margin, but this appears to be the result of contact with the stem (which also features the feltiness) in the button stage, rather than remnants of a true partial veil.

Gills: Free from the stem or narrowly attached to it; close; fragile and soft; whitish or pale yellowish, becoming rusty cinnamon; often gelatinizing somewhat in wet weather.

Stem: 3-12 cm long; up to nearly 1 cm thick; equal or tapering to the apex; hollow; fragile; finely scaly, powdery, or finely hairy--or more or less smooth; white with a yellowish apex and/or base, or yellowish overall.

Flesh: Insubstantial; yellowish.

Odor and Taste: Not distinctive.

Chemical Reactions: KOH on cap surface negative to dark gray.

Spore Print: Rusty brown.

Microscopic Features: Spores 10-16 x 6-9 µ; more or less elliptical, with a truncated end; smooth; with a pore. Brachybasidioles and cheilocystidia present. Basidia abruptly clavate. Pileipellis a hymeniform trichoderm.

REFERENCES: (Bulliard, 1789) Fries, 1838. (Fries, 1821; Saccardo, 1887; Atkinson, 1900; Kauffman, 1918; Smith, Smith & Weber, 1979; Watling, 1982; Arora, 1986; Hansen & Knudsen, 1992; Lincoff, 1992; Evenson, 1997; Barron, 1999; McNeil, 2006; Miller & Miller, 2006; Knudsen & Vesterholt, 2008.) Herb. Kuo 08300401, 01120607, 05080901, 05281101.

This site contains no information about the edibility or toxicity of mushrooms.


Bolbitius titubans

Bolbitius titubans

Bolbitius titubans

Bolbitius titubans

Bolbitius titubans
Spore print

Bolbitius titubans

Bolbitius titubans
Basidia and brachybasidioles

Bolbitius titubans

Bolbitius variicolor
Atkinson's 1900 description of Bolbitius variicolor

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Kuo, M. (2012, February). Bolbitius titubans. Retrieved from the MushroomExpert.Com Web site: