Collection location: Madison Heights, Pasadena, California, USA [Click for map]
I rarely see the red cracks supposedly diagnostic of this species, but all else matches well: subtomentose, brown, rimose to cracked cap; thick, faintly and slowly bluing flesh; ochre, large tubes; smooth, tough, yellowish stem with distinct red regions; yellowish-brown spores. Always associated with oaks (this one in lawn a few feet from base of oak). Full notes here.
Thanks for the correction, Darvin. And thanks for showing me the Boletaceae key on mykoweb.com, Douglas — fantastic! Hmmm, wonder where I went wrong in the Arora key…
And, yes, it does seem I messed up the spore measurements. The reticle is in microns, and reads about 10% too large. Going back with Gimp and re-measuring, I get 10.3-12.9 × 4.1-4.7 microns. Thanks for catching that, too.
Looks like Boletus subtomentosus. The spores are NOT truncate as in B. truncatus and the cap lacks red thus not B. dryophilus or B. chrysenteron. On your reference page you list the spores a basically subglobose – almost round (11-13×8-10um). Also, did you calibrate the objectives? and if so, what is the conversion factor so we can measure the spores from your photos?
This species, like quite a few other species in the Boletes of CA, there is a layer of tissue under the outer skin of the cap that is pinkish-red. You can see
this by cutting the cap with a sharp knife, and looking closely at the layers of tissue right at the cap surface.
In a lot of cases when the cap surface cracks this pinkish layer is exposed, but in other cases the cracks go through the pink layer, and you see the yellowish flesh beneath. Probably depends on the moisture in the air.
But there is some reports that B. truncatus doesn’t have this pinkish layer, but maybe I am making that up. But that looks just like B. chrysenteron, except the spores are different. So, not sure, some more details when the difference between B. chrysenteron and B. truncatus is known would good to see.
But all you want to know about the Boletes of CA you can find here:
(Nice photo of the spores by the way…)