Boletinellus merulioides

Boletinellus merulioides
Image Courtesy of Peter Katsaros
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Group of Fungi: Boletes

Family: Boletaceae

Latin Name: Boletinellus merulioides (Schwein.) Murrill

Synonym(s): Gyrodon merulioides (Schwein.) Singer

Common Name: Ash Tree Bolete

Description: Total height 1 1/4–3 in (3–7.5 cm); cap 1 5/8–5 in (4–12.5 cm) wide, somewhat irregular to distinctly kidney-shaped in outline, yellow-brown to red-brown, upper surface smooth, viscid when moist, margin incurved; spore-bearing surface bright yellow to dingy yellow in age, bruising slightly blue-green, consisting of numerous shallow irregular to elongated pores that are radially arranged and extend a short distance down the top of the stalk; stalk 3/4–1 5/8 in (2–4 cm) long, 1/4–1 in (0.5-2.5 cm) in diameter, expanding upwards, off-center and sometimes almost lateral; spores olive-brown in mass.

Biological Role: This fungus forms a symbiotic relationship with an insect, the leafcurl ash aphid (Meliarhizophagus fraxinifolii), that feeds on the roots of ash trees. This type of biological role is unique among the fungi considered on this web site.

Habitat: On the ground near ash trees; usually occurring in small groups.

Geographical Distribution: Widely distributed throughout eastern North America wherever ash is found.

Comments: The fact that Boletinellus merulioides is invariably associated with ash makes it easy to identify. In the symbiotic relationship mentioned above, the vegetative body of the fungus (or mycelium) forms little knots of tissue (called "sclerotia") that surround and protect the aphid. In return, the aphid produces a sugary solution (referred to as "honeydew") that is utilized by the fungus.

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