Parasitic Bolete

Description

The Parasitic Bolete is a small mushroom with a cap 2–6 cm across, dry, suede-like, dull yellow to olive-brown, cracked into small fields in dry weather. The underside consists of yellow tubes that turn olive-brown with age, and the stem is yellow, often curved and tapering towards the base. The flesh is yellowish and slightly blues when cut.

It is easiest to recognise by where it grows: exclusively on fruiting bodies of the common earthball, usually several together from a single earthball, on acidic sandy and peaty soils. It is rare in Poland and partially protected, so it should not be picked.

Confusion with the suede bolete (podgrzybek zajączek) is only apparent, because the latter grows on the ground, not on an earthball.

Identification features

Cap

Diameter 2–6 cm; hemispherical when young, later cushion-shaped, finally flattened. Surface dry, suede-like, coloured from dull yellow through greenish ochre to olive-brown or yellow-brown; in dry weather it sometimes cracks into small fields.

Hymenophore (underside of the cap)

Tubes adnate or slightly decurrent, angular; yellow when young, later brownish olive or brownish yellow.

Stem

Height 3–7 cm, thickness 0.4–2 cm. Solid, yellow to yellow-brown or olive, with a fibrous structure; tapering towards the base and usually strongly curved.

Flesh

Yellowish, lemon-yellow above the tubes, brownish in the lower part of the stipe; slightly bluing when cut. Taste mild, smell mushroomy. Do not taste the flesh.

Spore print and spores

Spore print dark olive to olive-brown. Spores ovoid-fusiform, pale yellow to honey-yellow, 12–18 × 4.5–6 µm.

Habitat and distribution

Ecology. A parasite on fruiting bodies of the common earthball (Scleroderma citrinum); usually 1–5 fruiting bodies of the bolete grow from a single earthball fruiting body. It grows in various types of deciduous forest, sometimes also outside forests, exclusively on acidic peaty and sandy soils.

Distribution. Europe and eastern North America. Rare in Poland: about 150 localities had been reported by 2020; listed in the Red List of Plants and Fungi of Poland in category R (rare). It is also on the red lists of, among others, Belgium, Denmark, Slovakia, Lithuania and Germany. In Poland it was under strict protection in 1983–2014 and is now under partial protection (Dz.U. 2014 item 1408).

Fruiting. In North America from July to September; in Poland there are no precise data (probably summer to early autumn).

What can it be confused with?

• Xerocomus subtomentosus (suede bolete; Polish: podgrzybek zajączek) — Similar in appearance, but it grows on the ground as a mycorrhizal fungus rather than on earthball fruiting bodies; the growth site alone practically rules out confusion.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• It is one of the few boletes that parasitise the fruiting bodies of another fungus, the common earthball.
• Described by Bulliard in 1790 as Boletus parasiticus; the genus Pseudoboletus was created for it by Šutara in 1991.
• On 30 June 1980 Poczta Polska (the Polish Post) issued a 2 zł stamp featuring this mushroom (as podgrzybek pasożytniczy) in the series "Inedible mushrooms under protection"; 9,800,000 copies were printed.
• The current Polish name "borowikowiec tęgoskórowy" was recommended in 2021, after the species was moved from the genus Xerocomus (podgrzybek) to Pseudoboletus.