Gyroporus cyanescens, commonly known as the bluing bolete or the cornflower bolete, is a species of bolete fungus in the family Gyroporaceae. First described from France in 1788, the species is found in Asia, Australia, Europe, and eastern North America, where it grows on the ground in coniferous and mixed forests.
The yellowish to buff cap surface is fibrous and roughened, and reaches up to in diameter. The thick stem, roughly the same color as the cap or lighter, is hollowed out into chambers. All parts of the mushroom turn an intense blue color within a few moments of bruising or cutting. The mushroom is edible, despite its hard stem. A less common variety occurs where the color change is to deep violet rather than blue. The bluing reaction results from the oxidation of a chemical called gyrocyanin.
Taxonomy
The species was first described scientifically by French botanist Jean Baptiste François Pierre Bulliard in his 1788 Herbier de la France. Later synonyms include Boletus constrictus by Christian Hendrik Persoon in 1801, Leccinum constrictum by Samuel Frederick Gray in 1821, Suillus cyanescens by Petter Karsten in 1882, and Leucoconius cyanescens by Günther Beck von Mannagetta und Lerchenau in 1923. The variety violaceotinctus was described by Roy Watling in 1969 from collections made in Michigan, USA.
The specific epithet is derived from the Ancient Greek κύανoς, meaning "dark blue", while the varietal epithet violaceotinctus means "having a violet tinge". It is commonly known as the bluing bolete or the cornflower bolete.
Description
The cap of G. cyanescens is initially convex, but flattens out in maturity, sometimes becoming shallowly depressed; it reaches a diameter of . The cap is dry, and ranges in color from buff to yellowish to pale olive, occasionally with darker streaks of color. Its surface is uneven, sometimes with wrinkles and pits. The cap margin is initially curved inward, and sometimes splits in maturity. The flesh is whitish to pale yellow, and has a brittle texture. On the underside of the cap, the pore surface is white to yellowish, sometimes with olive or tan tinges. There are roughly two circular pores per millimeter, and the tubes that comprise the pores are deep, but depressed around the top of the stem. Injury to the pores will cause them to stain first greenish yellow, then greenish blue or blue.
The stem is long by thick, and is either roughly equal in width throughout its length, or has a basal or middle swelling. The stem tissue is hard and brittle; it is initially stuffed with a soft pith that develops cavities, or becomes entirely hollow in maturity. Roughly the same color as the cap or lighter, the stem surface is dry and lacks reticulations. It is initially covered in coarse hairs that tend to disappear in maturity to leave a relatively smooth surface. All parts of the fruit body stain blue when cut or injured. The variety G. cyanescens var. violaceotinctus is nearly identical in appearance, but stains dark lilac to indigo when bruised. The odor and taste of the fruit bodies is indistinct.
The color of the spore print is pale yellow. Spores are ellipsoid, smooth, hyaline (translucent), and have dimensions of 8–10 by 5–6 µm. The basidia (spore-bearing cells) are club shaped, two- to four-spored, and measure 24–30 by 8–10 µm. Pleurocystidia (cystidia on the inner walls of the tubes) are light yellow brown in color, club shaped, infrequent, and measure 25–38 by 7.2 µm; the cheilocystidia (found on the tube edge) are colorless, numerous, and measure 32–47 by 7–10 µm. Clamp connections are present in the hyphae.