Polyporus tuberaster  (Jacq.) Fr. (1815)

All collections from California

Growing from an underground sclerotium.  It can get as big as 50 lbs. The sclerotium n the picture seems to be in a very early formation. For a picture of a well developed sclerotium see Mushrooms Demystified, Color Plate 151.

Spores: 10-14 x 4.5-5.8µ  Spore deposit: white