The problem is, few of the Suillus mushrooms know they are supposed to manifest all of these features at once. This makes some of them a little difficult to identify to genus--but once one gets a feel for what is "Suillusy," it is a fairly easy genus to identify in the field. As a general rule of thumb, I usually expect any potential Suillus to demonstrate at least three of the features above. Alternatively, if you have a microscope, the presence of bundled, dark brown to blackish cystidia in the tubes (see the illustration) is in itself a reliable indicator of the genus Suillus.

There are some very beautiful and impressive Suillus species--and, after fall rains, they can come up in stunning numbers. The genus Suillus is fascinating from a scientific perspective. Given the seemingly tentative way that Suillus is defined as a genus (usually more or less as I have done at the top of this page, with a checklist of characters that are not all demonstrated in all specimens), it is surprising how well the generic concept has held up over the years. The separate genus Fuscoboletinus, consisting mostly of Suillus-like mushrooms growing under larch or tamarack, did not fare as well, and was folded into Suillus (Bruns & Palmer, 1989; Kretzer et al., 1996).

Before DNA studies, theorizing about the evolution of Suillus relied mostly on the idea that the boletes evolved from gastromycetes. The frequently elongated, radial (and sometimes nearly gill-like) pores of many Suillus species tempted theorists to place the genus between gilled mushrooms and boletes in a transitional zone, often with Phylloporus, the so-called "gilled boletes," nearby. However, such theories were the result of what I have called simple "pattern recognition," rather than true evolutionary theorizing, and DNA studies have demonstrated that actual phylogenetic relationships cannot be so easily inferred from the physical appearance of mushrooms.

While the boletes have not received as much attention from molecular biologists as the gilled mushrooms, current DNA evidence places some puffballs and gilled mushrooms with the boletes. Suillus, it appears, is probably closely related to Chroogomphus and Gomphidius, among other genera. A 1996 study by Kretzer et al. found that most clades within Suillus (amended to include Fuscoboletinus) lined up neatly with the mycorrhizal host trees of the mushrooms, suggesting that ecology is a crucial determiner in the genus. In fact, specimens of Suillus granulatus collected under different hosts were revealed to be genetically distinct!