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Entoloma alboumbonatum

[Basidiomycota > Agaricales > Entolomataceae > Entoloma . . . ]

by Michael Kuo

This striking entolomatoid mushroom has a conic, white cap with a silky appearance and a protruding central "nipple." It looks a bit like a white version of Entoloma murrayi, which is yellow, or Entoloma quadratum, which is orange—and, like those species, it features cuboid spores that are 4-sided in profile view and look like little ice cubes. The stem of Entoloma alboumbonatum is also white, and remains so through development. The gills are initially white, but with maturity they develop the pink tones characteristic of entolomatoid gills and spore prints.

Entoloma alboumbonatum is the same as Entoloma conicum, according to Baroni (2017) and Largent (1994). I have not studied the type collections, but the two collections I have studied manifest enough differences that they should probably be treated separately:

  • The spores of Entoloma alboumbonatum are predominantly cuboid (4-sided in profile); the spores of Entoloma conicum are consistently 4- to 6-sided;
  • The stem of Entoloma alboumbonatum is white in youth and into maturity, and easily split open longitudinally; the stem of Entoloma conicum is dark gray to gray-brown throughout development (contrasting with the white cap and white basal mycelium) and not easily split;
  • The cap of Entoloma alboumbonatum is essentially white; the cap of Entoloma conicum is very pale brownish, with a whiter center;

These differences are mostly borne out in descriptions of the two species by Hesler (1963, 1967) and Peck (1872), who originally described Entoloma conicum as having a "dull watery cinnamon" cap and stem that was "brown with white mycelium at the base."

Thanks to Jo and Bob Solem for collecting, documenting, and preserving Entoloma alboumbonatum for study; their collection is deposited in The Herbarium of Michael Kuo.


Ecology: Saprobic; growing alone or gregariously; summer; eastern North America. The illustrated and described collection is from Maryland.

Cap: 1–3 cm across; conic to broadly conic, with a prominent central "nipple"; finely, radially silky; dry; the margin not lined; white to buff.

Gills: Narrowly attached to the stem; close or nearly distant; white at first, becoming pink; short-gills frequent.

Stem: 4–6 cm long; 3–4 mm thick; equal; dry; finely silky; hollowing; fragile and easily splitting longitudinally; whitish; basal mycelium white.

Flesh: Thin; white.

Spore Print: Pink.

Microscopic Features: Spores 8–10 µm; predominately 4-sided; with a 1–2 µm apiculus extending from one corner; smooth; hyaline to yellowish in KOH. Basidia 4-sterigmate. Hymenial cystidia not found. Pileipellis a cutis; elements 4–6 µm wide, smooth or slightly encrusted, hyaline to yellowish in KOH. Clamp connections not found.

REFERENCES: Hesler, 1967. (Noordeloos, 1981; Phillips, 1991/2005; Largent, 1994; Baroni, 2017.) Herb. Kuo 07281801.

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Entoloma alboumbonatum

Entoloma alboumbonatum

Entoloma alboumbonatum

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Kuo, M. (2019, September). Entoloma alboumbonatum. Retrieved from the MushroomExpert.Com Web site: