Boletus subcaerulescens (E.A. Dick & Snell) Both, Bessette & A.R. Bessette
A Porcini Mushroom
Basis for Listing
Boletus subcaerulescens (a fungi) is reported as occasional to common from eastern Canada south to West Virginia and west to Minnesota; however, the geographic range of the species has not been determined. Within Minnesota, it has been reported from only two sites: along Amity Creek in Lester Park, Duluth, southern St. Louis County (North Shore Highlands) and in a red pine plantation near the Willow River in General Andrews State Forest, Pine County (Mille Lacs Uplands). Given its limited known distribution, Boletus subcaerulescens was cassified as a special concern species in 2013.
Mushroom caps of B. subcaerulescens are 4-12 cm (1.6-4.7 in.) broad, rounded to flat, with a minutely hairy surface (Snell and Dick 1970; Smith and Thiers 1971). Cap color is yellowish-tan or brownish-tan to grayish red or grayish reddish brown; flesh is white and slightly pinkish below the cap surface. The odor is pleasant and taste mild. Tubes are white at first then yellow with a tinge of green; pores are small and bruise blue-green then fade to lavender and finally brown. The pores do not always turn blue-green, and the bluing may happen slowly. Stems are 7-13 cm (2.8-5.1 in.) long, 13-35 mm (0.5-1.4 in.) thick, and covered with a reticulum to the base. The stem is almost white when young then similar in color to the cap, only paler. The reticulum is colored like the rest of the stem, though it may be lighter or darker. The reticulum stains darkly when handled. The spore print is dark olive-brown. Spores are subfusiform, smooth, thin-walled, pale yellow, and 14.2-15.4 by 4.1-5.1 µm.
Two species similar to B. subcaerulescens are B. edulis (king bolete) and B. nobilissimus (noble bolete). Boletus edulis differs in having a yellowish-brown to reddish-brown cap, tubes that do not bruise blue, and a whitish to brownish stem, with a white reticulum above. The absence of dark staining reticulum distinguishes this species from B. subcaerulescens; B. nobilissimus has a yellow brown to deeper reddish-brown cap, a white to brownish stem, and tubes that do not bruise blue.
Boletus subcaerulescens is a mycorrhizal species that grows with plant roots and fruits on the ground in association with northern conifers and hardwoods (northern fire-dependent forest). In Minnesota, it is associated with Pinus resinosa (red pine) or near Picea glauca (white spruce), Abies balsamea, (balsam fir), Pinus strobus (white pine) and Betula sp. (birch) (northern mesic mixed forest) (Dentinger 2007; Dentinger et al. 2010). It was first reported in eastern Canada in association with Pinus banksiana (jack pine) but was subsequently reported with Pinus sylvestris (scots pine), Picea sp. (spruce), Betula sp., and Populus sp. (aspen) in a Picea abies (Norway spruce) plantation and with Tsuga canadensis (eastern hemlock).
Biology / Life History
Boletus subcaerulescens as a mycorrhizal species is assumed to reproduce by spores or from mycelium in the soil coming in contact with roots of a host tree. It is also believed to be a beneficial symbiont. Its biology has not been investigated.
Conservation / Management
The population of B. subcaerulescens in Pine County is vulnerable to any activity that removes the living trees on which it depends. Like other mycorrhizal species it is probably affected adversely by increased nitrogen concentration in the soil.
Best Time to Search
The best time to search for this species is mid-summer through fall, based on reports of its fruiting in Minnesota from July to October, but it has been reported to fruit as early as May in the eastern U.S..
Conservation Efforts in Minnesota
Boletus subcaerulescens is not yet reported from a well protected site in Minnesota. Additional surveys for this species are needed. It has not been encountered in surveys in western Minnesota or earlier surveys in northeastern Minnesota. Most of our knowledge is based on a Ph.D. thesis on the porcini group (Dentinger, 2007).