Lactifluus chrysocarpus

Lactifluus chrysocarpus E. S. Popov et O. V. Moro zova

MycoBank: MB 80096

Pileus 15–18 mm broad, conchate or reniform, plano-convex with slightly depressed centre and incurved pubescent margin, deep yellow, orange yellow (4A7–8), darker in the centre (up to 5A8), paler towards margin (4A6–7), entirely velutinous. Lamellae moderately distant, adnate, broadly adnate to arcuate, whitish, unchanging. Stipe 2–4 × 1–2 mm, eccentric, cylindrical, light yellow (4A4–5) to orange yellow (4A6—7), smooth, glabrous. Context thin, whitish. Milk not observed. Odour not distinctive. Taste not recorded. Spores 6.6–8.6 × 5.8–7.8 μm, Q = 1.1–1.3, subglobose to broadly ellipsoid with amyloid ornamentation of roundish warts 0.5–1.0 μm high, joined in complete reticulum, hilum 1.8–2.0 μm, suprahilar plage centrally amyloid. Basidia 42.4–51.7 × 8.0–9.5 μm, 2–4-spored, narrowly clavate, clampless. Pseudocystidia present as endings of lactiferous hyphae, 38.8–40.5 × 3.8–4.5 μm, cylindrical to flexuous, with brownish content in Melzer’s reagent, rare in hymenium, more abundant in pilei- and stipitipellis. Hymenophoral trama composed of interwoven, thin-walled hyphae 2–4 μm wide with scattered lactifers and rare sphaerocysts. Pileipellis a pluristratous hymeniderm composed of clavate, obovate or obpyriform thin-walled cells 17.0–25.5 × 13.5–18.2 μm that gives rise to abundant thick-walled hairs. Hairs 53.7–178.5 _ 5.5–7.5 μm, rarely up to 200 μm long, hyaline, possessing swollen base and tapering, occasionally bifurcate apex, with walls 2.0–2.7 μm thick, sometimes constricted or septate. Stipitipellis a pluristratous hymeniderm of clavate and obovate thin-walled cells with protruding scattered pseudocystidia. Subiculum well developed, whitish, composed of strands of thick-walled hyphae 2.5–4.0 μm wide with walls 0.5–1.5 μm thick.

Notes: Lactifluus chrysocarpus is similar to Lactarius multiceps S. L. Mill., Aime et T. W. Henkel described from Guyana (Miller et al., 2002) owing to small pleurotoid to eccentric basidiomata, originating from the subiculum, bright yellow to brownish yellow colouration and reticulate spore ornamentation. The new species differs first of all by the absence of thick-walled hairs in the stipitipellis (therefore glabrous stipe) and by smaller spores. A small yellow South American Lactarius epitheliosus Buyck et Courtec. (Courtecuisse, Buyck, 1991) thought to be closely related to L. multiceps (Miller et al., l. c.) possesses a normally developed central stipe and pileipellis without thick-walled hairs.

Fig. 1 Phylogenetic tree derived from Maximum Likelihood analysis, based on nrLSU data. Posterior probability (PP) values from the Bayesian analysis followed by bootstrap values from the Maximum Parsimony (BS, %) analysis are indicated above branches (PP/BS). PP values > 0.95 and BS values > 50 % are shown. Pleurotoid species are marked by grey circles. The newly described species are in bold.