Lactarius subgenus Russularia (Russulaceae) in South-East Asia: 2. Species with remarkably small basidiocarps Author Wisitrassameewong, Komsit Institute of Excellence in Fungal Research, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand, E-mail: komsit. w @ hotmail. com (corresponding author) & School of Science, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand & Research Group Mycology, Department of Biology, Gent University, K. L. Ledeganckstraat 35, 9000 Gent, Belgium Author Nuytinck, Jorinde Naturalis Biodiversity Center, Section National Herbarium of the Netherlands, P. O. Box 9517, 2300 RA Leiden, The Netherlands Author Hampe, Felix Research Group Mycology, Department of Biology, Gent University, K. L. Ledeganckstraat 35, 9000 Gent, Belgium Author Hyde, Kevin D. Institute of Excellence in Fungal Research, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand, E-mail: komsit. w @ hotmail. com (corresponding author) & School of Science, Mae Fah Luang University, 333 Moo 1, Thasud sub-district, Muang district, Chiang Rai 57100, Thailand Author Verbeken, Annemieke Research Group Mycology, Department of Biology, Gent University, K. L. Ledeganckstraat 35, 9000 Gent, Belgium text Phytotaxa 2014 2014-12-15 188 4 181 197 http://dx.doi.org/10.11646/phytotaxa.188.4.1 journal article 10.11646/phytotaxa.188.4.1 1179-3163 5147410 Lactarius perparvus Wisitrassameewong & F. Hampe sp. nov. ( Figs 3 & 6C ) MycoBank: MB 808628 Typus :— THAILAND , Chiang Mai province , Muang district , Doi Suthep-Pui National Park , Sangasabhasri Lane to Huai Kok Ma village , 1145 m elev., N18°48.62 E098°54.60 , 29/6/2012 , KW320 ( holotypus GENT !, isotypus MFLU !) . Pileus 5–7 mm diam., plane to applanate to slightly infundibuliform, with or without inconspicuous papilla in center; surface dry to greasy, smooth; margin deeply striate up to the center, irregularly crenulate to wavy, mostly slightly inflexed; grayish orange (5 B 4) to brownish orange (5 C 4) to light brown (5D5), grayish brown, turning brown (6 E 6) when old. Lamellae decurrent, 1–2 mm broad, subdistant, with 2–3 series of lamellulae, yellowish white (2 A 2) to pale yellow (3 A 3); edge concolorous. Stipe 9–12 × 1–2 mm , cylindrical to slightly broader at base, slender, centrally attached; surface greasy, smooth; brownish orange (6 C 5– C 6) to light brown (6D5–7), slightly strigose at the base with some concolorous hairs. Context thin in pileus, thinner than 0.5 mm ; yellowish white (2 A 2), fragile, hollow in stipe, pale brownish orange (5D5) with 10%KOH, unchanging with FeSO 4 ; smell indistinct; taste mild. Latex sparse, watery, taste mild. Basidiospores subglobose to ellipsoid, 7.7– 8.2 –8.7(–8.8) × 6.8– 7.3–7.4 –7.9 µm, Q = 1.04– 1.12–1.16 –1.24 (n=40); ornamentation amyloid, mostly forming an incomplete reticulum, not forming closed meshes; ridges irregular, up to 1 µm high, subacute; isolated warts numerous and sometimes grouped; plage mostly inamyloid or slightly distally amyloid, sometimes distinctly distally amyloid. Basidia 35–46 × 15–18 µm, subclavate, 4−spored, rarely 2−spored, with guttulate contents, with sterigmata 6–9 × 1.5–3 µm. Pleuromacrocystidia infrequent to moderately abundant, 46–57 × 10–15 µm, not emergent, subclavate to subfusiform, with mucronate apex, thin-walled. Pleuropseudocystidia scarce, 2–3 µm diam., not emergent to slightly emergent, subcylindrical, tortuous. Lamellae edge sterile, with abundant marginal cells and rare cheilocystidia; marginal cells 9–23 × 8–13 µm, cylindrical to subclavate; cheilocystidia scarce, 24–42 × 6–10 µm, embedded, irregularly subfusiform. Hymenophoral trama with abundant lactifers intermixed with rosettes of sphaerocytes. Pileipellis a cutis, 30–70 µm thick, composed of parallel hyphae which are sometimes slightly inflated and septate. Stipitipellis a cutis, 70–90 µm thick, a compact layer of cylindrical, thin-walled hyphae. Diagnosis: L. perparvus is characterized by this combination of characters: extraordinary small size, strong pileus striation, incomplete reticulate spores and a cutis as pileipellis structure. See comment above. Habitat: gregarious on soil between leaf litter, sometimes growing on a dried leaf, sometimes on steep slopes and bare soil, in montane broad-leaved forest dominated by Castanopsis spp. and Lithocarpus spp. Etymology: —perparvus meaning very small, very little Studied material: THAILAND , Chiang Mai province , Muang district , Doi Suthep-Pui National Park , Sangasabhasri Lane to Huai Kok Ma village , 1145 m elev., N18°48.62 E098°54.60 , 29/6/2012 , KW320 ( holotype GENT !, isotype MFLU !);−ibid., 5/7/2012 , KW337 ( GENT !, MFLU !) . Comments: —By extension of the whole genus Lactarius , L. perparvus is the smallest representative of L. subg. Russularia currently known in Thailand (note that in Lactifluus , the other genus of milkcaps, species with very small basidiocarps also occur). In the field this species could be confused with L. crenulatulus (see under this species). Besides the less reticulate spores, L. perparvus also has larger spores. Our phylogeny shows that the species is closely related to L. gracilis and L. glabrigracilis . Both species have a different stature: longer and very narrow stipe and a somewhat larger pileus with distinct and acute papilla and denser gills. L. gracilis is also easily recognized by the tufts of hairs at the pileus margin.