Boletinellus merulioides

Description
Mushroom Identification
History
Synonyms

Description

Boletinellus merulioides is a species of bolete fungus in the family Boletinellaceae. The cap is initially convex before becoming flattened to convex in maturity and attains a diameter of 5–20 cm. The cap surface is dry to slightly sticky, and smooth or covered with tiny fibrils. Its color ranges from yellow-brown to reddish-brown and will bruise dull yellow-brown. The flesh is yellow and, when cut, will either have no color reaction or change slowly to blue-green.

The fruit bodies are edible but of low quality, with an acidic taste. The mushrooms can be used in mushroom dyeing to produce light brown or dark orangish-brown colors, depending on the mordant used.

Grow on the ground scattered or in groups, almost always near ash (Fraxinea spp.), but rarely near maple and white pine. Unusual for boletes, it forms abundant sclerotia. These are spherical to roughly elliptical structures measuring 2–3 mm wide, which have a hard, black to the dark brown rind and a hollow internal medulla. The fungus's preference for growing near ash is not due to a mycorrhizal association between them, but rather because the fungus has a relationship with a parasitic aphid that occurs only on these trees. The aphid feeds on the tree roots, and shelters inside hollow sclerotia formed by the fungus in the soil, or attached to the root system. The aphid secretes carbohydrates and other nutrients that benefit the fungus.

The fungus is found in eastern North America, from eastern Canada south to Alabama and west to Wisconsin. It is also found in Mexico. A common species, it fruits in summer and autumn. It has also been reported in Asia (Japan).

Common names: Ash-tree Bolete.

Mushroom Identification

Ecology

Found under green ash trees and other ash trees; probably involved in symbiosis with the leaf curl ash aphid, Meliarhizophagus fraxinifolii; growing alone, scattered, or gregariously; summer and fall; widely distributed in eastern North America.
Cap

5-20 cm, irregular (nearly convex when young, becoming wavy and nearly vase-shaped, or more or less flat); light to dark yellowish-brown, or sometimes reddish-brown; dry, tacky when wet; bald; soft and leathery; sometimes bruising darker brown.
Pore Surface

Pores elongated radially, sometimes appearing almost like gills, with many cross-veins; tubes shallow; running down the stem; yellow to olive, bruising brownish to olive to almost blue (sometimes not bruising); tube layer not easily separable.
Stem

2-4 cm long; 0.5-2.5 cm thick; usually not central (sometimes nearly lateral); yellowish above, colored like the cap (or darker) below; sometimes bruising darker brown or, near the base, blue.
Flesh

Whitish to yellowish or yellow; sometimes bruising blue when sliced, especially in the base of the stem and/or just above the tubes.
Odor and Taste

Odor fragrant or not distinctive; taste not distinctive.
Chemical Reactions

Ammonia purplish red on cap surface; orangish to negative on flesh. KOH dark orange on cap surface; orange on flesh. Iron salts pale orange to negative on cap; bluish-gray on flesh.
Spore Print

Olive brown.
Microscopic Features

Spores 7-10 x 6-7.5 µ; smooth; ellipsoid. Pleurocystidia to about 35 x 10 µ; lageniform. Pileipellis is a cutis of mostly erect, cylindric elements 6-9 µ wide. Clamp connections are present.

History

The species was first described as Daedalea merulioides by Lewis David de Schweinitz in 1832, from collections made in Salem. William Alphonso Murrill transferred the species to the genus Boletinellus in 1909. It is commonly known as the "ash-tree bolete". Rolf Singer classified it in the genus Gyrodon, but it is not closely related to that genus genetically.