Suillus borealis

Description

Suillus borealis is a species of bolete fungus in the family Suillaceae. Found in western North America where it associates with western white pine (Pinus monticola).

This species is characterized by the presence of a veil but no annulus, the very dark brown color of the cap, and the white to pallid stipe, at least when young, with obscure glandulae on the surface. There are no other species in California with which it is likely to be confused. In other areas, it might be confused with S. luteus, but that species has a distinct annulus.

The species is considered to be an excellent edible mushroom.

Mushroom Identification

1. Cap

   7-11 cm broad when mature, convex when young, becoming broadly convex to plano-convex to plane or shallowly depressed at maturity, often with undulating or highly irregular outlines when very old; surface very viscid to glutinous, glabrous, but some pilei appearing streaked from gluten; color brown ("orange-cinnamon" to "vinaceous-cinnamon" to "cinnamon"), sometimes dark brown ("Mikado brown" to "Verona brown") on the disc, fading to pale brown ("light pinkish cinnamon" to "pinkish buff") on the margin; margin strongly incurved, typically strongly appendiculate when young, but glabrous in some pilei when older, sterile. Context 1-2 cm thick, when young whitish, becoming yellow with age, changing to yellow when exposed in young basidiocarps. Taste and odor mild.

2. Tubes

   Up to I cm long, shorter near the margin, adnate to broadly and shallowly depressed, yellow ("old gold"), unchanging when exposed; pores ą1 mm broad, angular, concolorous, unchanging when bruised.

3. Stipe

   2-4 cm long, 1.5-2 cm thick at the apex, equal, solid to stuffed; surface dry, glandulae not strongly apparent when young but becoming so with maturity; color white when young, becoming reddish-brown ("tawny" to "ochraceous-tawny"), frequently bright yellow at the apex, sometimes staining pale brown at the base; no annulus. Context white to yellow, unchanging when exposed.

4. Spores

   6-8.5 X 3-5 µ, hyaline in KOH, yellowish in Melzer's, subellipsoid to subcylindric, smooth, thin-walled.

5. Spore Print

   Brown.

6. Basidia

   25-31 X 8-11 µ, clavate, four-spored, hyaline. Hymenial cystidia rare to absent on sides of tubes, abundant to crowded on the pores, dark brown in KOH and Melzer's, heavily incrusted, occasional hyaline clusters with only the base discoloring in KOH; individual cystidia 30-54 X 7-13 µ, cylindric to clavate, thin-walled.

7. Tube Trama

   Strongly divergent from a distinct mediostratum, subgelatinous in KOH, hyaline. Pileus trama interwoven, homogeneous, hyaline to pale brown in KOH. Pileus cuticle differentiated as a layer of interwoven to tangled hyphae 3-4 µ wide, gelatinous, hyaline to pale brown in KOH, rust-brown in Melzer's. Stipe cuticle differentiated as a layer of gelatinous hyphae with numerous large fascicles of cystidia staining dark brown in KOH. Clamp connections absent.

8. Chemical reactions

   KOH-context vinaceous; FeSO4-context gray.

9. Habit, habitat, and distribution

   Gregarious to subcespitose in soil in mixed pine-oak woods. Known only from a single collection made under pines in the vicinity of Willow Creek in northern California. This species was originally described from Idaho but is now known from throughout the Pacific northwest. It appears to be associated with five-needle pines, but further data are necessary before its mycorrhizal host can be accurately determined.

Photo sources:

Photo 1 - Author: brendanblack (CC BY 4.0)

Photo 2 - Author: brendanblack (CC BY 4.0)