Boletus pinetorum is an edible bolete fungus in the family Boletaceae. Generally found in Fennoscandia, it was described as a new species in 2009 from a collection made in Finland. It resembles the popular Boletus edulis but is distinct from that species genetically. Fruitbodies of B. pinetorum have greyish brown caps with wrinkled margins. The bolete is mycorrhizal with pines, and grows in dry sandy pine heaths and dry coniferous forests.
Boletus pinetorum was formally introduced as a new species by Korhonen, Liimatainen and Niskanen in their 2009 study of the Boletus edulis complex in Fennoscandia. The authors compared six taxa in Boletus sect. Boletus occurring in Finland, using both traditional morphological characters and DNA sequence data from the internal transcribed spacers (ITS1, ITS2) and the intergenic spacer region IGS1. Although molecular analyses did not fully resolve relationships within the B. edulis group, consistent differences in spore shape, the dimensions and shape of caulocystidia (specialised cells on the stipe), and the structure of the pileipellis (cap cuticle) supported recognition of B pinetorum as a distinct species.
The cap (pileus) measures 15âÂÂ25 cm across (occasionally up to 30 cm), its surface smooth to almost smooth and greyish brownâÂÂsometimes yellowish or dark brownâÂÂand becoming slightly viscid when wet. The margin may appear gently wrinkled when mature. On the underside is the hymenophore, composed of tubes 2âÂÂ4 cm long that begin yellow, turn greenish yellow and finally greyish yellowâÂÂgreen; the small, round pores match the tube colour. The stipe (stem) is 13âÂÂ17 cm tall and 3âÂÂ5 cm wide, cylindrical or tapering slightly at the base, whitish with a brownish tint and overlaid by a distinct, white reticulation (netâÂÂpattern) whose meshes measure up to 10 by 2 mm. The flesh is firm and white, tinged yellowish brown beneath the cap cuticle, with a pleasant taste and a strong, agreeable aroma.
Microscopically, spores are elongated (fusiform), smooth, thickâÂÂwalled and measure 16.5âÂÂ19 by 5.5âÂÂ6.5 micrometre (üm) (average 17.5 by 5.8 üm). CaulocystidiaâÂÂflaskâÂÂshaped cells on the stipe surfaceâÂÂare 70âÂÂ160 by 13âÂÂ30 üm and broader at the tip. The cap cuticle (pileipellis) consists of long, variably pigmented hyphae whose terminal cells are cylindrical to slightly clubâÂÂshaped, 30âÂÂ60 by 6âÂÂ12 üm.
Boletus pinetorum forms ectomycorrhizal associations exclusively with Pinus sylvestris (Scots pine). It is most often encountered in dry, sandy pine heaths and dry to moderately moist coniferous forests, fruiting later in the season than many other boletes (typically late summer). To date it has been recorded from across Fennoscandia, including Finland, Sweden and Estonia.