Suillus granulatus is an introduced species associated with Pinus in the temperate zone of the northern hemisphere and is widely distributed in both Europe and North America. The relatively large degree of variability encountered in Suillus granulatus over its natural geographical range has resulted in the recognition of a large number of infraspecific taxa. Of the more recent attempts to divide the species the most comprehensive treatments are those of Singer (1945a) and Blum (1965).

Singer distinguished four subspecies on the basis of minor differences in spore size, small differences in colour of the fruitbodies, geographical distribution, and mycorrhizal associations in nature. The results of applying this classification to New Zealand specimens are inconclusive, for many collections possess spore and colour characters intermediate between two subspecies. However, it should be noted that Singer's classification arose from observations on specimens growing in their indigenous habitats. It is possible that under New Zealand conditions, where both fungus and mycorrhizal partner have been introduced, a degree of morphological modification of Suillus granulatus has occurred, with the result that subspecific differences are no longer distinct. The high degree of taxonomic significance attached to mycorrhizal associations of the subspecies by Singer (1945a) is not supported by field observations in New Zealand. No constant differences could be found between specimens growing under Pinus strobus and P. pinaster, although according to Singer these specimens should belong to Suillus granulatus ssp. snellii Singer and ssp. leptopus (Pers.) Singer respectively.

Blum (1965) recognised five varieties of S. granulatus based primarily on spore size and colour differences in the fruitbodies. As with Singer's scheme, it is not possible to place New Zealand specimens with any degree of certainty using this classification.

In view of the difficulties in assigning them to any of the described subspecific taxa, New Zealand collections are simply referred to the species. Smith and Thiers (1964) also encountered difficulty in defining S. granulatus ssp. snellii, the subspecies restricted to North America, and relegated it to the excluded species. Smith and Thiers (1966) later concluded that a number of variants of S. granulatus existed, in which small variations in spore size were apparently correlated with certain groups of the genus Pinus. Four variants were distinguished on this basis but because of the small differences involved, it was considered not worth naming them.

Suillus granulatus is an excellent edible fungus but as with most Suilli, the mucilaginous pellicle of the pileus should first be removed,

S. granulatus may be recognised by the buff yellow, tan, or reddish tan pileus, presence of glandulae on the stipe, and absence of an annulus. Which was first recorded from New Zealand by Walker (1931).