On the underside on the cap is the spore-bearing tissue consisting of minute vertically arranged tubes that appear as a surface of angular, yellowish pores.

The presence of milky droplets on the pore surface of young individuals, especially in humid environments, is a characteristic feature of this species.

An ectomycorrhizal species, S. pungens forms an intimate mutualistic relationship between its underground mycelium and the young roots of the associated host tree.

The fungus—limited in distribution to California—fruits almost exclusively with Monterey and bishop pine, two trees with small and scattered natural ranges concentrated in the West Coast of the United States.

The fungus's propensity to fruit prolifically despite minimal root colonization is a result of its ability to efficiently transfer nutrients from its host for its own use.

[2] A 1996 molecular analysis of 38 different Suillus species used the sequences of their internal transcribed spacers to infer phylogenetic relationships and clarify the taxonomy of the genus.

The results suggest that S. pungens was genetically similar to S. collinitus, S. neoalbidipes, S. pseudobrevipes, S. luteus, S. brevipes, S. weaverae, and certain isolates of S. granulatus.

The flesh is 1–2 cm (0.4–0.8 in) thick, white and unchanging in young fruit bodies, frequently changing to yellow when older.

[1] The tubes that comprise the hymenium (spore-bearing tissue) on the underside of the cap are up to 1 cm (0.4 in) long, adnate when young, becoming decurrent or nearly so with age.

They appear dark brown when mounted in a dilute (3%) solution of potassium hydroxide (KOH), and are cylindric to roughly club-shaped, measuring 43–79 by 7–10 μm.

Its taste is harsh, nauseating, and weakly acidic;[1] the odor is strong and ranges from pleasant, resembling bananas, to pungent.

[5] When collecting for the table, young specimens are preferred, as older ones "literally seethe with fat, agitated maggots and sag with so much excess moisture that they practically demand to be wrung out like a sponge!

Suillus pungens has been misidentified as S. placidus because of the white color of the young fruit bodies and the droplets of exudate.

The cap of S. granulatus is variable in color, ranging from pale yellow to various shades of brown, while the pore surface is initially whitish, later becoming yellowish, and similar to S. placidus, its typical host is eastern white pine.

Although it occurs most frequently in the autumn and winter,[5] it is one of the few species of Suillus that continue to fruit sporadically throughout the year,[1] especially in wet weather.

Once established, genets vegetatively spread hyphae out from the root tip into the soil and may connect two or more trees to form a network of mycorrhizae.

This result indicates that the fungus persists because of extensive vegetative growth, rather than frequent establishment of new genets from spores, and that it uses carbon resources efficiently.

[17] The large S. pungens genet was not detected after wildfire, demonstrating that it did not survive in the absence of a host, and suggesting that spores are the primary means by which the fungus recolonizes after a fire.