Iodine bolete

Description

The iodine bolete is a rare bolete with a cap 5-12 cm across, cream-grey to beige-brown, felty in young specimens, with a fine silvery bloom. The pores and tubes are lemon to golden-yellow and do not change colour when damaged. The stem is yellowish, without a net, rough, often with a reddish band under the tubes. The flesh does not turn blue, and at the base of the stem it smells medicinal, like phenol or iodoform; this smell intensifies during cooking.

It grows from May to mid-October in warm, sunny broadleaved forests, parks and gardens, most often under oaks, in lowlands and foothills, usually on calcareous ground. It is rare in Poland.

It is distinguished from similar boletes by the lack of blueing of the flesh and pores and by its characteristic smell. Because of its rarity it is best not to collect it at all; if you have any doubts about the identification, do not eat it.

Identification features

Cap

Diameter 5-12 cm, exceptionally up to 20 cm; at first hemispherical, then arched, cushion-shaped, almost flat in mature ones. Colour in young ones cream-grey with an olive tinge, then cream-olive to beige-brown (in descriptions also from light tan, through chestnut-brown to grey-brown). Cuticle at first felty, covered with a silvery-grey, finely thread-like bloom that fades with age; bald in older specimens. Turns brown when damaged; in drought it may crack. A drop of ammonia stains the cuticle violet.

Hymenophore (underside of the cap)

Poroid; tubes 15-30 mm long, lemon-yellow, then golden-yellow, olive-greenish in old ones; do not change colour when cut (rarely turn slightly green-brown). Pores small, round, lemon to golden-yellow, do not change colour when pressed or rarely turn brown. Attachment to the stem - no data.

Stem

Height 5-18 cm, thickness 2-8 cm (descriptions give different ranges); at first bulging and massive, then cylindrical, spindle-shaped or club-shaped. Colour pale yellow, then yellow-greyish, lemon at the top. Never has a net; surface rough, granular to slightly fibrous, with small lumps. Often a reddish or brown-reddish band under the tubes, at the base sometimes pinkish or reddish flecks. Mycelium at the base white.

Flesh

Whitish, whitish-yellowish to pale lemon, darker above the tubes and at the base of the stem (to yellow-brown); does not change colour when cut (rarely turns slightly pink-brown). In the stem somewhat fibrous. Smell unpleasant, medicinal, reminiscent of phenol or iodoform, strongest at the base of the stem and intensifying during cooking. Taste mild.

Spore print and spores

Spore print olive-brown. Spores spindle-shaped to ellipsoid, smooth under the light microscope, without a germ pore; dimensions 10-16 × 4-6 µm, usually 11-14 × 4.5-5.5 µm. Under SEM small warts are visible.

Habitat and distribution

Ecology. A mycorrhizal fungus (ectomycorrhiza) with oaks; occasionally with beech, sweet chestnut, linden, hornbeam. According to some descriptions it prefers calcareous ground and warm, sunny sites; according to others it is not tied to a particular substrate (recorded on both calcareous and acid).

Distribution. Europe; widely in the temperate and southern parts of the continent, confirmed molecularly, among others, in Estonia, France, Germany, Portugal, Spain, Sweden, Cyprus and Sardinia. Rare in Poland; Red list 2006: E (endangered). Not legally protected in Poland (Dz.U. 2014 item 1408), but because of its rarity it deserves protection.

Fruiting. From May to mid-October.

What can it be confused with?

• Hemileccinum depilatum — Sister species; cap wrinkled or "hammered", associated with hornbeam or hop-hornbeam; also differs in the structure of the cap cuticle (palisadoderm).
• Leccinellum lepidum — Cap sticky, wrinkled, does not turn violet with ammonia; flesh slowly turns violet-grey and black; longer spores (up to 20 µm).
• Xerocomus subtomentosus (suede bolete) — No lumps on the stem; pores larger, angular, turn blue when pressed; flesh at the bottom of the stem pink-brown.

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

• The name impolitum means "rough" and refers to the felty cuticle of the cap, visible under a hand lens.
• The characteristic iodoform smell (medicinal, phenolic) makes it possible to recognise it after cutting the stem at the base.
• The old Polish name "borowik płowy" was replaced by the recommended name "płowiec jodoformowy", because in Polish literature this species was confused with Lanmaoa fragrans.
• In the genus Hemileccinum only two species occur in Europe.