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The Genus Boletus
by Michael Kuo
The mushrooms in Boletus, as the genus is traditionally defined, are boletes that do not typically have scabers or glandular dots on their stems. Their spore prints are olive brown to brown (a few species with yellowish or rusty spore prints, often included in Boletus, are officially placed in Xanthoconium but are treated here with Boletus). They have solid stems, and their pores are not typically elongated and radial (as in some species of Suillus). Under the microscope, their spores are not ornamented.
Boletus is currently the largest genus of boletes, containing over 150 species in North America--but the writing is on the wall and it is clear that big taxonomic changes are coming soon to a Boletus in your viewing area. Check out just about any recent DNA survey of the boletes (this one from Hibbett & Binder, 2004, is handily online), and you will soon discover that "Boletus" is an incoherent label, genetically. The trouble is, we are still at the broad survey stage, and the hard work of collecting and testing the many hundreds and thousands of specimens that will be required in order to assert species and genera with confidence hasn't even started.
Identifying species of Boletus, therefore, should be placed in contemporary context: much of what we thought we knew is likely to be upturned in the near future. Identifying Boletus species has never been particularly easy, anyway; it has always been a frustrating endeavor (though not quite as frustrating as identification in Leccinum), and one is constantly finding mushrooms that do not quite fit any description. To have much success with identification, you will definitely need to have fresh specimens representing several stages of development; the mushrooms in Boletus often change their appearance rather drastically as they develop.
Specific identification pitfalls include cap color and bruising or staining changes. In general, color is one of the most unreliable features for mushroom identification (which is why looking at photos in field guides is an unsuccessful way to identify mushrooms!) . . . but with mushrooms in Boletus, one is especially likely to encounter problems with cap color. A mushroom described as having a black cap is not likely to have a white one, of course, but the brownish- and reddish-capped mushrooms in Boletus (which is most of them) are frequently variable in color, and subject to color changes due to weather conditions. As far as bruising or staining goes, you will need to be sure to check such reactions with fresh mushrooms, preferably within an hour of picking them. Waiting too long may produce unreliable results. And do not be surprised if you encounter faint staining or bruising where it should not happen, according to many descriptions.
Key to Boletus and Xanthoconium in North America
Note: This key is in bad need of revision. The non-dichotomous format is annoying and, with the hindsight of a few years, I see many areas that require different emphasis, fleshing out, paring down, and so on. Don't hold your breath waiting, but I will eventually revise the key completely. For species in the Boletus edulis cluster, see the Key to 12 North American edulis-like Boletes. Several very good keys are included in the references list, below.
Species of Xanthoconium, Retiboletus, and Chalciporus are included in this key. Species of Xerocomus (a European genus name sometimes applied to North American mushrooms) are included, but are treated as Boletus species.
> Cut flesh in cap or stem staining bluish to blue on exposure. (1/2).
> Cut flesh in cap or stem not bluing on exposure (though the pore surface may bruise blue). (2/2).
° Stem reticulate on mature mushrooms, over at least the upper portion. (1/2)
~ Stem orange yellow, not bruising; cap surface flashing faintly slate blue with ammonia; cap color bright orange-yellow; taste not distinctive or slightly acidic. (1/3)
~ Stem rose to red, bruising brownish to olive; cap surface yellowish olive with ammonia; cap color dull red, becoming reddish orange; taste not distinctive. (2/3)
~ Stem pale to pinkish tan or grayish olive, bruising olive to brownish; cap surface flashing pale slate or staining blue with ammonia; cap color whitish to grayish, becoming pinkish tan; taste mild or bitter. (3/3)
° Mature stem not reticulate. (2/2)
~ Stem smooth, pale to pinkish tan or grayish olive, bruising olive to brownish; cap color whitish to grayish, becoming pinkish tan; taste mild or bitter. (2/4)
~ Stem smooth or with yellow powder, red to orange to yellow, not bruising; cap color yellow to orange yellow; taste not distinctive. (3/4)
Arora, D. (1986). Mushrooms demystified: A comprehensive guide to the fleshy fungi. Berkeley: Ten Speed Press. 959 pp.
Arora, D. (2008). California porcini: Three new taxa, observations on their harvest, and the tragedy of no commons. Economic Botany 62: 356-375.
Bessette, A. E., Roody, W. C. & Bessette, A. R. (2000). North American boletes: A color guide to the fleshy pored mushrooms. China: Syracuse UP. 399 pp.
Binder, M. & D. S. Hibbett. (2004). Toward a global phylogeny of the boletales. Retrieved from the Clark University Web site: http://www.clarku.edu/faculty/dhibbett/boletales_stuff/Global_Boletales_2004_28S.gif
Both, E. E. (1993). The boletes of North America: A compendium. Buffalo NY: Buffalo Museum of Science. 436 pp.
Coker, W. C. and Beers, A. H. (1943). The boleti of North Carolina. New York: Dover. 96 pp. (1971 reprint.)
Grand, L. F. & Lodge, D. J. (1978). Occurrence of Boletus piedmontensis in North Carolina and Georgia. Mycologia 70: 1267-1268.
Grund, D. W. & Harrison, A. K. (1976). Nova Scotian boletes. Germany: J. Cramer. 283 pp.
Scates, K. (2004). Trial field key to the boletes in the Pacific Northwest. Retrieved from the Pacific Northwest Key Council Web site: http://www.svims.ca/council/Boletes.htm
Singer, R. (1945, 1947; reprint 1977). The Boletinae of Florida. Germany: J. Cramer.
Smith, A. H. & Thiers, H. D. (1968). Notes on boletes–I. 1. The generic position of Boletus subglabripes and Boletus chromapes. 2. A comparison of four species of Tylopilus. Mycologia 60: 943-954
Smith, A. H. & Thiers, H. D. (1971). The boletes of Michigan. Ann Arbor: U Michigan P. 428 pp. An online version of this book is available here, at the University of Michigan Herbarium (URL too long for duplication).
Smith, A. H., Smith, H. V. & Weber, N. S. (1981). How to know the non-gilled mushrooms. Dubuque, Iowa: Wm. C. Brown. 324 pp.
Snell, W. H. & Dick, E. A. (1970). The boleti of northeastern North America. Germany: J. Cramer. 115 pp.
Thiers, H. D. (1975). The boletes of California (online reprint of California mushrooms: A field guide to the boletes). Retrieved from the MykoWeb Web site: http://www.mykoweb.com/boletes/index.html
Thiers, H. D. (1976). Boletes of the southwestern United States. Mycotaxon 3: 261-273.
Cite this page as:
Kuo, M. (2010, March). The genus Boletus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/boletus.html