Lactifluus pseudohygrophoroides H. Lee & Y.W. Lim

Index Fungorum number: IF553809 Facesoffungi number: FoF 03647

Etymology: ‘pseudohygrophoroides’ refers to its similarity to L. hygrophoroides (Berk. & M.A. Curtis) Kuntze.

Holotype: SFC20140821-45

Pileus 45–85 mm diameter, planoconvex with central depression to infundibuliform; margin slightly rugulose when young; edge even, sometimes undulate; surface smooth, sometimes irregular, pruinose, pale orange (6A3) to pale red (9A3). Lamellae adnate to subdecurrent, distant, white to pale cream, broad; edge entire and concolourous. Stipe 30–70 × 10–20 mm, stuffed, cylindrical, sometimes slightly tapered downward, centrally attached to pileus; surface dry, pruinose, concolourous with pileus, sometimes paler. Context solid, white, unchanging; smell not distinctive. Latex not very abundant, white, unchanging. Basidiospores broadly ellipsoid, sometimes subglobose, 8.6–9.3–9.8 × 7.2–7.6–8 μm (n = 20, Q = 1.13–1.21–1.30); ornamentation amyloid, forming an almost complete reticulum, composed of very low warts connected by fine ridges, up to 0.2 μm high; plage inamyloid. Basidia 4-spored, 55.7–65.9 × 10.9–12.5 μm, subclavate to clavate; content guttate to granular. True cystidia absent. Pleuropseudocystidia scarce, 6–8 μm, cylindrical; content granular. Pileipellis a lampropalisade; elements of the suprapellis 37–95 × 2–4 μm, cylindrical, obtuse, thick-walled; subpellis 112–137 μm thick, sphaerical cells 12–35 μm diameter, with thickened wall.

Material examined: KOREA, Seoul, Gwanak-gu, Seoul National University, N37°27′09″ E126°57′09″, alt. 163 m, on soil in mixed forest, with Pinus strobus and Quercus spp., 21 August 2014, H. Lee & Y.W. Lim (SFC20140821-45, holotype); KOREA, Gangwon-do, Wonju-si, Mt. chiak, N37°22′11″ E128°03′03″, alt. 1118 m, on soil in mixed forest, with Pinus densiflora and Quercus spp., 13 August 2015, H. Lee & Y.W. Lim (SFC20150813-71, paratype)

GenBank numbers SFC20140821-45 ITS:MF611657; LSU:MF611682; RPB2:MF617784. SFC20150813-71 ITS:MF611656; LSU:MF611681; RPB2:MF617783.

Notes: Lactifluus pseudohygrophoroides belongs to L. subg. Pseudogymnocarpi sect. Pseudogymnocarpi. In the multiple-locus phylogeny, the species is closely related with L. hygrophoroides (Berk. & M.A. Curtis) Kuntze from North America. L. hygrophoroides is considered as a variable species and four varieties of the species have been described in Hesler and Smith (1979): L. hygrophoroides var. hygrophoroides, L. hygrophoroides var. odoratus, L. hygrophoroides var. rugatus and L. hygrophoroides var. lavendulaceus.

Undoubtedly, this Korean species can be confused with L. hygrophoroides due to similar morphology such as pruinose and orange to reddish pileus, white latex with unchanging reaction on exposure, absence of true cystidia and lampropalisade. Both species can only distinguish from each other based on basidiospore ornamentation and molecular data. The majority of basidiospores observed in L. pseudohygropharoides have a dense and complete reticulum in spore ornamentation. Here we also provide comparison of selected morphological characters and ecology between L. pseudohygrophoroides and 4 varieties of L. hygrophoroides that have been described in the monograph of Hesler and Smith (1979).

Comparison of morphological characters and ecology between L. pseudohygrophoroides and 4 varieties of L. hygrophoroides

Morphology and ecology L. pseudohygropharoides L. hygrophoroides
var. hygrophorides var. odoratus var. rugatus var. lavendulaceus
Pileus colour Pruinose, pale orange to pale red Pruinose, reddish tawny to dull cinnamon Velvety, apricot buff to cinnamon buff Velvety, orange brown Dull orange to orange brown
Latex colour White, unchanging White, unchanging White, unchanging White Milk-white, slowly at times becoming brown
Basidiospore 8.6–9.3–9.8 × 7.2–7.6–8.0 μm, mostly dense complete reticulum, up 0.2 μm 7.5–9.5(10.5) × 6–7.5 μm, small warts connected by fine lines, 0.2–0.4 μm 7–9.5 × 5.5–7.5 μm, partial reticulum, with finer lines, 0.2–0.4 μm 7.5–9 × 6–7.5 μm, partial reticulum, with isolate warts, up to 0.5 μm 7–9.4 × 6–7.5 μm, broken reticulum, with isolate warts, 0.2–0.5 μm
True cystidia Absent Absent Absent Absent Not observed
Pileipellis Lampropalisade, thick-walled, terminal cells 37–95 × 2–4 μm Lampropalisade, thick-walled, with turfs of pileocystidia, terminal cells 10–60 μm long Lampropalisade, thick-walled, with turfs of pileocystidia, terminal cells 22–50 × 3–8 μm Lampropalisade, thick-walled, with turfs of pileocystidia, terminal cells 100 × 2–5 μm Lampropalisade, thick-walled, with turfs of pileocystidia, terminal cells 40–150 × 2–3 μm
Ecology In mixed forest, Quercus spp. and Pinus strobus In deciduous forest In coniferous forest Not recorded Not recorded

Phylogram generated from maximum likelihood (RAxML) analysis based on combined ITS, LSU, RPB2 sequence data of Lactifluus. ML bootstrap support values greater than 70% are indicated above or below the nodes and the new species are in bold. The tree is rooted with species in other Russulaceae genera. Superscript T after specimen number represents as a type specimen

Lactifluus pseudohygrophoroides (SFC20140821-45, holotype). a, b Fruiting bodies in the field (SFC20140821-45). c Basidia. d Basidiospores. e Marginal cells. f Pleuropseudocystidia. g Pileipellis