|Major Groups > Boletes > Boletus > Xanthoconium purpureum|
by Michael Kuo
Xanthoconium purpureum is one of the most common boletes in my area (central Illinois). For years I assumed it was Xanthoconium affine--but that species is brown, rather than purplish to reddish brown, and its cap surface does not flash green when a drop of ammonia is applied.
Aside from the color of the cap and the ammonia reaction, distinctive features for Xanthoconium purpureum include the lack of any dramatic bruising or staining on its surfaces, and the yellow-brown spore print. In my experience it also develops a distinctive, somewhat foul and bad-meat-ish odor at just about the time the spores mature.
Ecology: Mycorrhizal with oaks, or with Eastern White Pine; growing alone, scattered, or gregariously; early summer through fall; probably widely distributed east of the Great Plains, but often reported as "Xanthoconium affine."
Cap: 3-7 cm, convex to broadly convex in age; dry; smooth or very minutely velvety; purplish red to maroon or reddish brown, fading to tan.
Pore Surface: Whitish, becoming yellowish brown; not bruising, or bruising vaguely brownish; pores circular; tubes to 1.5 cm deep.
Stem: 5-8 cm long; .5-1.5 cm thick; more or less equal; smooth; pale at apex, streaked with the cap color below.
Odor and Taste: Not distinctive with most specimens; odor often becoming foul (like bad meat) as the spores mature.
Chemical Reactions: Cap surface flashing green with ammonia, but negative with KOH.
Spore Print: Bright yellow-brown.
Microscopic Features: Spores 9-13 x 3-4 µ; smooth; subfusoid. Pileipellis a tightly packed trichoderm with inflated, clavate or subclavate terminal elements--an "epithelium."
"Boletus purpureofuscus" is an invalidly published synonym.
REFERENCES: Snell & Dick, 1961. (Snell & Dick, 1961; Snell & Dick, 1970; Smith, Smith & Weber, 1981 [B. purpureofuscus]; Both, 1993; Bessette, Roody & Bessette, 2000.) Herb. Kuo 06019505, 06269505, 06130208, 06300705, 07010702, 07040703.
Specimens with whitish- to yellowish-spotted caps (see the illustration) are not uncommon, and are suggestive of "var. maculosus" in Xanthoconium affine . . . which suggests (to me, anyway) the possibility that purplish colors and an ammonia reaction might not be the most accurate means of separating species.
Malformed, contorted specimens of Xanthoconium purpureum are frequently encountered, growing alongside their more normal counterparts. These specimens often develop rudimentary pore surfaces that have "normal" looking basidia but produce contorted, oddly shaped spores.
Further Online Information:
Xanthoconium purpureum at Boletes of Central NY
Cite this page as:
Kuo, M. (2007, December). Xanthoconium purpureum. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/xanthoconium_purpureum.html