It’s fully autumn now and despite frosty nights and sometimes cooler days, this is a good time to hunt for mushrooms. At this time of the year, there are many interesting species popping up from the duff, through the moss, the sides of rotting logs, and even from fallen pine needles.
Boletes, a broad term for genera of pore fungi, have been sprouting in the woods these last few weeks. One afternoon in early October I came upon Suillus spectabilis, the larch bolete. It wasn’t a very handsome specimen, as some animal, perhaps a mouse or red squirrel, had taken some big chunks out of the cap. This reddish mushroom grows in conifer swamps where tamarack or larch (coniferous trees in the genus Larix) occur forming an ectomycorrhizal association. Two other Suillus (Suillus cavipes, Suillus grevillei) that also form ectomycorrhizal associations with Larix were noted in the area.
Finding Suillus spectabilis helped to solve another Suillus identification problem. This other Suillus species was growing on some high ground near the edge of the tamarack swamp but also just a few yards away from a white pine the ectomycorrhizal associate another bolete: Suillus spraguei (syn. Suillus pictus). Given the close proximity to two possible symbionts, I wasn’t sure whether this mushroom was growing in association with pine roots or tamarack roots. Now that I had a new red Suillus for comparison, the differences were immediately obvious. I could now add the pine bolete or Suillus spraguei to the fungi checklist.
The differences between the two species, aside from the conifers they associate with, are seen in the cap, pores, and stem. For Suillus spectabilis (see here, here, and here), the cap is reddish with large pink scales; the pore surface is at first yellow, later turning brown; the margin of the cap’s underside is thin and the edge is not inrolled, and the stem is more or less equal in width from top to bottom, fibrillous and reddish.
Suillus spraguei (see here, here, and here) has a cap covered in red-brown scales; the underside is yellowish, later fading to brown; the cap margin is inrolled when young, and the stem may be a little wider at the base than at the top.
Boletes such as Suillus have undergone taxonomic revisions in recent decades clarifying genus and species delineations using molecular phylogeny. The genus is divided into three subgroups: Granulatus, Tomentosus, and Spectabilis. Subgroup Spectabilis includes Suillus spectabilis while subgroup Granulatus includes Suillus spraguei. Members of subgroup Spectabilis form ectomycorrhizal associations with Larix (larch, tamarack) and Pseudotusga (Douglas fir). Those in subgroup Granulatus form ectomycorrhizal associations with Pinus (pines) and one species is ectomycorrhizal with pines and Quercus (oaks). Ectomycorrhizal associations with Pinus in the subgroup Granulatus are further partitioned between two-needle and five-needle pines.
Nhu H. Nguyen, Else C. Vellinga, Thomas D. Bruns, Peter G. Kennedy (2016). Phylogenetic assessment of global Suillus ITS sequences supports morphologically defined species and reveals synonymous and undescribed taxa. Mycologia, 108(6), 2016, pp. 1216–1228. DOI: 10.3852/16-106, 2016 by The Mycological Society of America, Lawrence, KS 66044-8897