Zeller's Bolete

Appearance

The cap is typically between 4–12 cm in diameter, initially convex but flattening somewhat in maturity. It is fleshy, with an uneven velvety surface, and dark brown to nearly black; the margin of the cap is a pale cream color. Young specimens are covered by a grayish bloom.

The tubes that comprise the undersurface of the cap are up to 1.5 cm long and angular, yellow, becoming dirty yellow and finally greenish-yellow; there are 1–2 pores per millimeter on the hymenium surface. They may turn slightly brownish when exposed to the air for a time. The flesh is yellow to dirty yellow, up to 1.5 cm thick, and inconsistently bruises blue when cut or broken. The stem is up to 12 cm tall, 1–3 cm thick, and swollen toward the base. The stem surface is red or yellowish with red lines, often white or yellow at the base, and solid, with fibrous flesh; in maturity the stem ages to yellowish-red to dark red. The spore print is olive-brown; one source notes that creating a spore print may result in "a lot of yellow juice on the paper".

The spores are ellipsoid in shape, smooth, and have dimensions of 12–16 by 4–6 µm, although occasionally there will be some "giant spores" with lengths of up to 24 µm. The basidia, the spore-bearing cells, are 26–35 by 9.5–12 µm, and four-spored. The cystidia are roughly cylindrical and thin-walled, with dimensions of 38–77 by 5.5–14.8 µm. There are no clamp connections present in the hyphae. The fruit body tissue stains a greenish color when a drop of ammonia solution is applied.

Naming

The red-cracked bolete has an olive-brown cap that cracks, exposing flesh that ages to pinkish red. "Boletellus chrysenteroides", found only in eastern North America, has a velvety to smooth, dark reddish brown, cracked cap with pale exposed flesh. Also similar is "Boletus mirabilis".

Distribution

This species grows solitarily or in small groups on the ground or in forest duff in mature coniferous forests, occasionally abundant on grassy edges of the forest, rarely on badly decayed conifer logs. It is an ectomycorrhizal mushroom, meaning that the fungal hyphae form sheaths around the rootlets of certain trees, exchanging nutrients with them in a mutualistic relationship. The fungus associates with alder, poplar and other hardwoods, and has been shown in laboratory culture to form ectomycorrhizae with Western Hemlock. However, the fungus may have saprobic tendencies, as it has been noted to grow under California Redwood, a tree not known to form mycorrizhae. It is known to form long rhizomorphs, and has been noted to be more abundant in sites with buried wood than without. In British Columbia, it occurs from summer to early winter, although it also appears infrequently in early spring. In California, the mushroom often fruits after the rainy period in autumn through to March or April. The dark coloring of the cap make this species difficult to notice, "unless a glimpse of the yellow hymenium is obtained". Fruit bodies are eaten by the American shrew-mole.

"Xerocomellus zelleri" is distributed in North America in the Pacific Northwest south to California and Mexico. In Mexico, it has been reported in high-altitude cloud forests of Mexican Beech, a rare and endangered habitat. It has also been reported from Tibet, but this may be based on a misidentification.

Habitat

This species grows solitarily or in small groups on the ground or in forest duff in mature coniferous forests, occasionally abundant on grassy edges of the forest, rarely on badly decayed conifer logs. It is an ectomycorrhizal mushroom, meaning that the fungal hyphae form sheaths around the rootlets of certain trees, exchanging nutrients with them in a mutualistic relationship. The fungus associates with alder, poplar and other hardwoods, and has been shown in laboratory culture to form ectomycorrhizae with Western Hemlock. However, the fungus may have saprobic tendencies, as it has been noted to grow under California Redwood, a tree not known to form mycorrizhae. It is known to form long rhizomorphs, and has been noted to be more abundant in sites with buried wood than without. In British Columbia, it occurs from summer to early winter, although it also appears infrequently in early spring. In California, the mushroom often fruits after the rainy period in autumn through to March or April. The dark coloring of the cap make this species difficult to notice, "unless a glimpse of the yellow hymenium is obtained". Fruit bodies are eaten by the American shrew-mole.

"Xerocomellus zelleri" is distributed in North America in the Pacific Northwest south to California and Mexico. In Mexico, it has been reported in high-altitude cloud forests of Mexican Beech, a rare and endangered habitat. It has also been reported from Tibet, but this may be based on a misidentification.