The aspen bolete or orange cap (Leccinum insigne) is a familiar sight in the aspen groves of the Arizona high country. It is good tasting and common, and in good years can be quite abundant. For these reasons it is avidly sought by many edible mushroom enthusiasts in Arizona and the Rocky Mountain states.
Leccinum insigne is an obligate mycorrhizal partner with the quaking aspen, Populus tremuloides, but looks confusingly similar to other Leccinum species such as the birch bolete and may overlap with them in part of its range. The taxonomy of the Leccinum genus is in some turmoil, so suffice it to say that what you think is an aspen bolete may not be exactly the same as an aspen bolete you’ve eaten before.
Unfortunately, evidence is accumulating that certain Leccinum strains and certain individual mushroom eaters do not get along. A few people in Colorado and elsewhere have become quite seriously ill after consuming what seemed to be ordinary aspen boletes.
Huge numbers of these mushrooms are consumed every year without ill effect, but each person eating an aspen bolete will want to be extra careful. If you’ve never eaten them before, make sure you take the usual precautions when trying a new mushroom, especially starting with a small bite and waiting a day or two to see if it agrees with you. And if you gather Leccinum from a new site, or especially from under a different host tree, you may be well advised to do likewise. Cooking them thoroughly is also a good idea, as with any wild mushroom.
Update 8-28-2014: An informative discussion of this topic can be found at the Cascade Mycological Society website.