Collection location: Howarth Park, Santa Rosa, Sonoma Co., California, USA [Click for map]
Fruiting under Monterey pine. 4.5cm. Has both yellow and reddish stains on exterior. Spore mass is dingy gray and bruised or stained yellow.
If the specimen was found in sandy soils under either Ponderosa or Lodgepole pine, then I would suggest Rhizopogon occidentalis. This is a common species, especially in coastal areas. The rhizomorphs on the outside of the peridium should stain yellowish to orange. When absolutely mature, there is a greay-green gleba (interior) that has an odor of bananas. I call it the banana truffle for that reason. It is edible, as aree most known Rhizopogons that are curently known.
Looking at the “Field guide to N. American Truffles”, there are some options. The closest thing looks to be R. ellenae – which is “fairly common” with pine, and stains vinaceous to yellow-brown when handled. It doesn’t mention the gleba staining (in any Rhizopogon), but the gleba will start white, and go from yellow to olive in age. Is the yellow staining a bruising reaction, or just the spores forming? There is also R. atroviolaceus which looks similar, but the spores will stain purple in iodine, and is rare. There is also R. roseolus which whitish when young, but quickly stains rose red when handled, and R. occidentalis, but the rhizomorphs on the surface are yellow-orange in that one,
I find that the “field” guide is a little frustrating, there isn’t any help in figuring out a species, only a list of 90 species with photos. Also there isn’t much of a hint how “complete” they think the guide is. And it isn’t really “truffles”, but various hypogeous fungi, including secotiod ones like Thaxogaster, Gastroboletus, Atcangeliella, and even Sarcophaera. Of the genus Tuber there are 11 species, so this guide is a mixed bag. I don’t think it is really wort a going rate of $16.95, unless you really want to know about some truffles you find. I got it on sale, so it is good enough for me I guess, cute but slightly strange and frustrating.