Cornflower Bolete

Description

The cornflower bolete is a medium-sized bolete with a straw-yellow or cream, suede-like cap (3.5–12 cm). Its hallmark is instant bluing: just touch or cut the fruiting body and the pores, tubes and flesh turn an intense blue. The stem is thick, without a ring, and with age it is chambered or hollow inside.

It grows from July to November in deciduous and mixed forests, on sandy soils, under pines, birches, oaks and beeches, especially in the mountains and foothills. In Poland it is rare and is listed on the Red List of fungi (status R), so collect it sparingly.

The bluing often puts mushroom pickers off, but it is a trait of this species. Even so, other boletes also turn blue, so before picking make sure of the remaining features: white or cream tubes, straw colour, no ring and a hollow stem.

Identification features

Cap

Diameter 3.5–12 cm. Arched when young, then cushion-shaped, finally flat, sometimes slightly depressed; the margin is initially inrolled and may crack at maturity. Surface dry, suede-like, covered with a thick fibrous felt, sometimes wrinkled. Colour cream, straw-yellow or sulphur-yellow with a yellow-green tinge, fading to whitish with age. Dark blue spots appear where it is pressed.

Hymenophore (underside of the cap)

Tubes 5–10 mm long, white or cream, initially attached to the stem, later free (depressed around the stem); they turn blue when cut. Pores small (about 2 per mm), angular-rounded, initially white, cream with age, sometimes with an olive tinge; when touched they turn yellowish-green, then blue.

Stem

Height 4–12 cm, thickness 1–3 cm; irregularly cylindrical, thinner at the top or swollen at the base or in the middle. Colour the same as the cap or paler. Surface dry, felty, without a net pattern, bare at the top. The inside is initially spongy, later divided into chambers or completely hollow; the tissue is hard and brittle. No ring. Turns intensely blue where crushed.

Flesh

White or yellowish, brittle, turning blue quickly (almost instantly) and intensely when cut or damaged. Taste and smell insignificant. The blue colour results from the oxidation of gyrocyanin.

Spore print and spores

Spore print pale yellow (straw). Spores ellipsoid or ovoid, smooth, pale yellowish to translucent. Size: 8–15 × 4–6 µm (descriptions give different ranges).

Habitat and distribution

Ecology. Mycorrhizal fungus (ectomycorrhiza) with a wide range of hosts; most often under pines, birches, oaks and beeches, also poplars. Grows on the ground, on sandy soils, at forest edges and on road banks. Fruiting bodies are sometimes attacked by the mould Sepedonium ampullosporum.

Distribution. North America (mainly east of the Rocky Mountains), Europe, Asia and Australia. Rare in Poland; on the Red List of plants and fungi of Poland (2006) it has the status R (rare, potentially threatened because of its limited range and small habitat areas). It is not under species protection in Poland. It also appears on the threatened lists of Austria, Germany and the Netherlands. It grows in deciduous and mixed forests, especially in the mountains and foothills.

Fruiting. From July to November (descriptions give different periods; some indicate summer and early autumn).

What can it be confused with?

• Gyroporus phaeocyanescens — Smaller, cap dull brownish-yellow; the flesh turns blue, but the yellow pores do not; larger spores (9–15 × 5–7 µm).
• Gyroporus castaneus (chestnut bolete) — Related; cap rusty brown and no bluing.
• Suillus tomentosus — Brownish pores turn blue more slowly.
• Caloboletus marshii — Turns light blue, but not at the base of the stem.
• Young Russula fellea (geranium-scented russula, bitter russula) — It can be confused if you look only at the top of the cap; the russula has gills and brittle flesh, not tubes; always dig up the whole fruiting body.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• The bluing is caused by gyrocyanin, a compound discovered in 1973; in other boletes, bluing is linked to the oxidation of variegatic or xerocomic acids.
• The epithet cyanescens comes from the Greek kyanos — dark blue.
• The variety violaceotinctus turns dark lilac to indigo when damaged and is used for dyeing non-woven fabrics.
• The Polish name was given by Alina Skirgiełło in 1960.