Boletus campestris

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by Michael Kuo

If you're an enthusiastic mushroom identifier and you have lots of time on your hands, try picking a little, brick-capped bolete with a yellow, blue-staining pore surface and sitting down to figure out what you've picked. Boletus campestris is virtually indistinguishable from Boletus fraternus, Boletus rubellus, and several other less frequently encountered mushrooms (including small forms of the usually larger Boletus bicolor).

Some field guides advise amateurs that the mushrooms in this species complex are so similar that a microscope is needed to make an accurate identification. But in this case even using a microscope (at least, using a microscope to the extent that an amateur mycologist like me can use one) provides only a little assistance; spore sizes and shapes for the various species in question are close, and the cellular structures of the cap surfaces are either inconsistently documented or documented but too similar to be of much use. In the end, one often winds up relying on a very close and careful reading of the mushrooms' macrofeatures. See the "Campellus Calculator" in the right-hand column for help separating this species from its closest look-alike, Boletus rubellus.

Theoretically, then, Boletus campestris is separated from its close cousins by its macrochemical reactions; its (usual) habitat in grassy, open places; its small pore openings (1-3 per mm); and the shape of its stem, which is relatively slender and equal, and does not typically taper to a point at the base.

The edibility of some of the mushrooms in this species complex has not been determined--so, obviously, since Boletus campestris is so difficult to identify with certainty, it should not be collected for the table.

Description:

Ecology: Presumably mycorrhizal with hardwoods, though I suppose there is a small chance it is saprobic; found in open, grassy areas (but generally not too far from trees) or in woods; summer and fall; east of the Rocky Mountains, or in Texas.

Cap: 2-4 cm; convex, becoming broadly convex or nearly flat in age; dry; smooth or finely velvety; the surface cracking up slightly by maturity, especially towards the margin; rosy red to brick-red, fading somewhat.

Pore Surface: Yellow, becoming greenish yellow; bruising fairly quickly blue to blue-green; 1-3 circular to angular pores per mm; tubes to about 1 cm deep.

Stem: 3-7 cm long; .5-1 cm thick; more or less equal, not typically tapered at the base; yellow above, usually colored like the cap below; not reticulate; solid; with yellowish basal mycelium.

Flesh: Yellow; staining blue to greenish blue on exposure. Not orange in the very base of the stem like Boletus rubellus according to Bessette, Roody & Bessette (2000).

Odor and Taste: Not distinctive.

Chemical Reactions: Cap surface negative with ammonia; flesh negative (but blued areas erased) with ammonia. Cap surface "bright yellow" with KOH (Smith, 1973); flesh reaction to KOH not reliably recorded in literature, but I have found it to turn dull orange. Reactions to iron salts not reliably recorded in literature, but in my experience negative on flesh, and negative to dull orangish or pale olive on cap surface.

Spore Print: Olive brown.

Microscopic Features: Spores 11-15 x 4.5-7 µ; smooth; irregularly ellipctical.

REFERENCES: Smith & Thiers, 1971. (Smith, Smith & Weber, 1981; Weber & Smith, 1985; Arora, 1986; Phillips, 1991/2005; Lincoff, 1992; Both, 1993; Horn, Kay & Abel, 1993; Metzler & Metzler, 1992; Bessette, Roody & Bessette, 2000.) Herb. Kuo 08010202, 06150301, 07160302, 08240502.

Further Online Information:

Boletus campestris in Smith & Thiers, 1971
Boletus campestris at Roger's Mushrooms

The calculator assigns points for Boletus rubellus ("R") and Boletus campestris ("C"). Calculate the total points for "R" and "C," then base your identification on the species receiving the most points. If the difference between your point totals is less than 2 and you have not measured the spores, you should consider your results tentative. You should also consider the possibility that DNA studies will eventually conflate these two species, and your effort will have been pointless.

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Cite this page as:

Kuo, M. (2004, November). Boletus campestris. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/boletus_campestris.html