Cap depressed to funnel-shaped, velvety or tomentose, later smooth, cap margin inrolled and remaining so for a long time. Gills forking. Spore print rusty, brownish or vinaceous.
At least eight species are described in Europe. With exception of Paxillus rubicundulus, that is relatively easy to recognize, the rest of the species gravitate closely around Paxillus involutus.
The colour of the spore print is thought to be important for the species recognition, so it should be thoroughly noted when freshly deposited. The crystal that occur in the rhizomorphs are also considered important so any Paxillus collection must contain fruitbodies with preserved basal mycelium.
Reaction with ammonia solution is used to separate some of the species. It has been proven in other bolete genera that the ammonia reaction has little (if any) taxonomic value. However, it has not been evaluated in Paxillus and it should be tested systematically.
Paxillus zerovae Wasser
Known to me from the description in the literature. Cap small-sized, 1.5–2.5 cm in diam., reddish brown, scaly in the center, smooth towards the margin. Stipe cylindrical or curved, olive coloured. Gills not forking, dark yellowish olive to olive brown. Flesh bright ochraceous in the cap, whitish cream in the stipe, unchanging when exposed to air. Spore print brown. Spores 10.1–11.7 × 3.2–3.9 μm, finely ornamented under scanning electron microscope.
Habitat. In pine forests on sandy soils.
Distribution. Described and so far only known from Ukraine. Should be carefully looked for.
Note. The ornamented spores are distinctive feature of this species (see Pegler & Young 1981).
No photographs of this species are available to me so far, nor have I seen any on the internet. The species is so far overlooked by the European mycologists. Diagnosis and Latin and description in Russian are published by Wasser (1973). The original diagnosis is reprinted in Akulov & Prydiuk (2007), who also provide English translation of Wasser’s description. Description and SEM microphotograph of the spores is found in Pegler & Young (1981).
Akulov O.Yu. & Prydiuk M.P. 2007. The preliminary checklist of boletoid fungi of Ukraine. – Pagine di Micologia 27: 117–144.
Pegler, D.N. & Young, T.W.B. 1981. A natural arrangement of the Boletales, with reference to spore morphology. – Transactions of the British Mycological Society 76: 103–146. (available online)
Вассер, С.П. 1973. Paxillus zerovae S. Wasser sp. nov. новий вид iз Степової зони Української РСР. – Украинский ботанический журналь 30(5): 667–668. [Wasser, S.P. 1973. Paxillus zerovae S. Wasser sp. nov., a new species from the steppic zone of Ukraine. – Ukrainian Journal of Botany 30(5): 667–668.].