Suillus piperatus is an introduced species indigenous to temperate regions of the northern hemisphere. Of the two commonly recognised varieties of this species, var. piperatus and var. amarellus (Quel.) Singer, New Zealand collections agree with the type variety. The possession of a reddish hymenophore is an unusual character among the Suilli. This character, together with the absence of both glandulae and an annulus, led Singer (1938) to erect the section Piperati to accommodate Suillus piperatus. Two further species were later transferred to this section by Singer. Smith and Thiers (1964) excluded sect. Piperati from Suillus on the grounds of a number of features correlated with the reddish hymenophore, but did not suggest an alternative disposition of the section.

Suillus piperatus also differs physiologically from other Suillus. Tyler, Benedict, and Stuntz (1965) showed that of the 17 species of Boletaceae tested for urea accumulation, including nine species of Suillus, only S. piperatus showed a moderate level of urea; the remainder were urea-negative. It would be of interest to see whether tests on S. rubinus (W. G. Smith) O. Kuntze and S. rubinellus (Peck) Singer, the remaining two species included in sect. Piperati by Singer (1962), produced similar results.

It has been shown in Europe and North America that S. piperatus is capable of forming mycorrhizal associations in nature with many genera of conifers as well as angiosperm genera such as Fagus, Quercus, Betula, and Populus. In New Zealand, the species has been collected only under introduced conifers. Rawlings (1951) recorded its association with Pinus contorta var. latifolia and P. ponderosa, in addition to the two species named above.

The peppery taste of Suillus piperatus makes it unsuitable for eating in quantity. However, it is not a poisonous species and may be added in small quantities to other edible species to sharpen the flavour.

S. piperatus is characterised by the dry to slightly mucilaginous pileus, reddish hymenophore, absence of glandulae and an annulus, and small fruitbodies. Was first recorded from New Zealand by Rawlings (1951).