[2] The genus Suillus was first defined by Pier Antonio Micheli in his 1729 work Nova plantarum genera, however it is not valid as it predates the 1753 start of Linnean taxonomy.

Setting Suillus luteus as the type species, he described the genus as those mushrooms with a centrally placed stipe, a distinct ring, a circular cap, and tubes that are stuck together.

[a] Structures of the fungi in this genus in common with other members of the order Boletales include the presence of a cylindrical stipe, cap, soft flesh and tubular hymenium.

Specific characteristics common to most species in Suillus are the cap cuticle which is often slimy and sticky when moist, the presence of darkly staining, clustered, sterile cells called cystidia that give the tube mouths or the stipe surface a speckled or glandular appearance, spores that are usually cinnamon brown or chocolate brown in mass, and obligate mycorrhizal relationships primarily with members of the Pinaceae, especially with members of the genera Pinus, Larix and Pseudotsuga.

The pores are bright yellow in S. collinitus, cinnamon in S. variegatus and grey in S. viscidus; in shape they are round in S. luteus and angular in S. bovinus.

[8] Some Suillus species are edible and are highly esteemed, particularly in Slavic countries, where they are generally referred to as butter mushrooms (маслята).