Suillus pungens, commonly known as the pungent slippery Jack, or the pungent suillus, is a species of fungus in the genus Suillus. The fruit bodies of the fungus have slimy convex caps measuring up to 14 cm (5.5 in) wide. The mushroom is characterized by the very distinct color changes that occur in the cap throughout development. Typically, the young cap is whitish, later becoming grayish-olive to reddish-brown or a mottled combination of these colors. The mushroom has a dotted stem up to 7 cm (2.8 in) long, and 2 cm (0.8 in) thick. On the underside on the cap is the spore-bearing tissue consisting of vertically arranged minute 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. S. pungens can usually be differentiated from other similar Suillus species by distribution, odor and taste. The mushroom is considered edible, but not highly regarded.
An ectomycorrhizal species, it fruits almost exclusively with the Monterey and Bishop pine, two trees with small and scattered natural ranges concentrated in the West Coast of the United States. Several studies have investigated the role of S. pungens in the coastal Californian forest ecosystem it occupies. Molecular phylogenetics has shown that although the species produces more fruit bodies than other ectomycorrhizal fungi at the same site, it is not a dominant root colonizer, occupying only a small percentage of ectomycorrhizal root tips. Its ability to fruit prolifically despite minimal root colonization is explained by its ability to efficiently transfer nutrients from its host.