Suillus luteus

Suillus luteus is a species of bolete fungus commonly referred to as slippery jack or sticky bun. The fungus was originally assigned to Boletus by Carl Linnaeus in 1753, before being made the type species of Suillus in 1796. The slimy cap is typically up to 10 cm (4 in) wide and conical before flattening. A membranous partial veil connects the cap to the stem when young. Yellow tubes extend downward from the underside of the cap, which spores escape through. The pale stem is up to 10 cm (4 in) tall and 3 cm (1+1⁄4 in) thick, bearing small dots near the top. Unlike most other boletes, it bears a distinctive membranous ring, tinged brown to violet on the underside.

A common fungus native all across Eurasia from Ireland to Korea, it has been introduced widely elsewhere, including North and South America, southern Africa, Australia and New Zealand. The fungus grows in coniferous forests in its native range, and pine plantations in countries where it has become naturalized. It forms symbiotic ectomycorrhizal associations with living trees by enveloping the tree's underground roots with sheaths of fungal tissue. The fruit bodies are often produced in large numbers above ground in summer and autumn.