Truffle Genus: Rhizopogon
 Rhizopogon clavitosporus basidiospores scale = 10 µm |
Kingdom: Fungi Phylum: Basidiomycota Order: Boletales Family: Boletaceae |
Spore Characters
Surface: Smooth or rarely minutely roughened.
Shape and Size: Mostly longitudinally symmetrical and cylindrical to fusoid (spindle-shaped) mostly 5-12 x 2-4 µm, but some species have ellipsoid or irregularly shaped spores, 12-15 (-20) x 5-8 µm; attachment straight, inconspicuous to truncate-cupped.
Wall: Single, thin except for a few species with walls up to 2 µm thick; apical pore lacking.
Color in Water: Hyaline to pale yellow; spores that are individually hyaline are often yellow to pale olive or pale brown in mass.
Melzer's Reaction: No reaction for most species, but spores of sevceral in subgenus Amylopogon turn gray to deep purple.
Comments: The genera Alpova and Truncocolumella are close relatives of Rhizopogon; because the spores of all three are similar, these genera must be separated on the basis of other structures. Spores of Gastroboletus spp. cannot be dependably separated from those of Rhizopogon except in spores of Gastroboletus species with the attachment nipple angled to the spore axis. Two relatively infrequent species in the genus Trappea, T. darkeri of the Pacific Northwest and T. phillipsii of Northern California, will also key out in the Rhizopogon group in a spore key. The spores of these two species are almost never longer than 5 µm, however, whereas Rhizopogon spores are never shorter than 5 µm. Rhizopogon is the only truffle-like genus that has some species with spores that are both smooth and turn purple in Melzer's reagent.
View photos of Rhizopogon spores
Sporocarp Characters
Shape and Size: Globose to pyriform (top-shaped) or irregular, 1-9 cm in diameter, with some species occasionally reaching up to 15 cm.
Peridium: White to brown-yellow, salmon, brown, red-brown, or red, often darker on top than at the base. In many species, staining pink to brick red or brown; ranging in thickness from 0.5-2 mm. Some species are totally smooth or felty, but most have rhizomorphs appressed at least around the base and sides, and some have peridia composed entirely of interwoven rhizomorphs. A drop of potassium hydroxide (KOH) solution on fresh peridium produces a gray to olive, blue, brown, red, or black reaction on most species.
Gleba: White or yellow in youth, with small chambers that are usually empty but in some species filled with spores. At maturity, becoming olive, olive-gray, olive-brown, orange-brown, or black-brown.
Odor: Depending on species, fruity, wine-like, cheesy, or spicy-pungent.
View photos of Rhizogopon sporocarps