Gastrosuillus, once considered a distinct genus, has been shown with molecular analysis to be a recent evolutionary derivative of Suillus. Fuscoboletinus, described by Pomerleau and Smith in 1962, has also been subsumed into Suillus.
The reevaluation of Gastrosuillus as a separate genus through molecular analysis revealed it to be a relatively recent evolutionary offshoot from Suillus. Likewise, Fuscoboletinus, previously described by Pomerleau and Smith in 1962, has also been reclassified under the Suillus genus.