Ink Stain Bolete

not listed

NNR - Unranked

not listed

Ink Stain Bolete is a late season, blue staining mushroom. It occurs in eastern Europe and in North America. In the United States it occurs in the east from New Hampshire to North Carolina, west to Minnesota and Tennessee. It also occurs in the Pacific Northwest from Washington to northern California. In Minnesota it occurs only in the southeast quarter of the state. It is found in summer and fall in deciduous and mixed forests, in parks, and in gardens. It grows on the ground, alone, scattered, or in groups, usually under oak and beech trees, occasionally under conifers. It has a mutually beneficial relationship (mycorrhizal) with the tiny rootlets of trees, absorbing sugars and amino acids while helping the tree absorb water.

When it first appears, the cap is convex, dark brown to blackish-brown, and covered with fine, velvety hairs. As it ages it expands and the color lightens. Mature caps are broadly convex, hairless, and 1½″ to 4″ (4 to 10 cm) in diameter. The upper surface may be dry or moist. It sometimes develops cracks, revealing the yellowish flesh below, and develops reddish tints within the cracks. It quickly turns bluish-black when bruised.

The pore surface is yellow when young, becoming brownish-yellow as it ages. It instantly stains dark blue when bruised. There are 1 to 2 pores per millimeter. The pore tubes are angular and up to ⅝″ (15 mm) deep.

The stalk is solid, 1½″ to 3″ (4 to 8 cm) long, and ⅜″ to 1″ (10 to 25 mm) thick. It is more or less equal from top to bottom but is sometimes tapered toward the base. The surface has raised ridges, but the ridges do not join and form a network (reticulate). The stalk is bright yellow at the top and reddish-brown to brown below. Like the cap, it quickly turns bluish-black when bruised. When sliced the flesh of the stalk rapidly turns bluish-black when exposed to air.

The flesh is mostly yellow, red just at the base of the stem. It instantly stains blue when exposed to air. The rapid, dark, bluish-black staining of the entire mushroom is the feature that gives the mushroom its common name. Some other boletes also stain blue but not as dramatically.

Ink Stain Bolete is edible but undesirable. A recent study (Braeuer et al., 2018a) showed that it hyper-accumulates organic arsenic, dimethylarsinic acid (DMA), from the soil. DMA is carcinogenic, so eating Ink Stain Bolete is not recommended.

Deciduous and mixed woodlands, parks, and gardens

Hardwoods, especially oak and beech; occasionally on conifers

Summer and fall

Sources

4, 26, 29, 30, 77.

This species was originally described as Boletus pulverulentus. It was transferred to the new genus Cyanoboletus in 2014.

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Location: Saint Croix Bluffs Regional Park