Lactarius friabilis
Lactarius friabilis H.T. Le & Stubbe
MycoBank number: 510723
Pileus 25-55 mm diam., plano-convex, centre slightly depressed, often with an inconspicuous papilla; margin somewhat irregularly wavy and striate to slightly grooved, becoming irregularly crenate when older; surface velutinous, dry, dark cream-coloured (4B3/4, 5A2) to pale yellowish brown (5DE4-5) or warm coffee-and-milk coloured and with an olive brown tinge (4DE4) (slightly reminiscent of the colours of L. fluens Boud.), but paler towards the margin; extreme margin dark cream-coloured. Lamellae adnate or subdecurrent, rather distant to subdistant, 4-10 mm broad, often interconnected by anastomosing veins, abundant, short lamellulae present, whitish (5A2) or pale yellow to greyish yellow (4(5)AB3/4), staining pinkish, orange-pinkish or brownish pinkish by the latex; edge entire, concolourous. Stipe 20-45 × 4-10 mm, central or slightly eccentric, rather slender, equal or slightly tapering downwards, sometimes curved at base; surface dry, smooth, paler than lamellae, yellowish white (4/5A2/3), staining slightly dirty orangish pink (6C3/4) to orange (6A8) when bruised. Context rather thin in pileus, stuffed in stipe, white, staining pinkish or orange-pinkish after cutting (5A3, 6B4, 7A5, 7B6, 7C8, 8B5), remaining white in the centre of the stipe; smell faintly fragrant or mealyspermatic, reminiscent of L. azonites (Bull.) Fr. Latex abundant, white or watery white, drying pinkish, unchanging when isolated. Spore print colour unknown. Basidiospores (6.3) 7.8–7.9–8.4–9.1 × (5.8)7.1–7.5–7.8–8.7 (8.9) μm (Q = 1.01–1.04–1.08–1.15; n = 120), globose to subglobose; ornamentation amyloid, a somewhat dense but incomplete reticulum with various free terminal ends, composed of rather irregular ridges that are 1.5-2 (2.5) μm high, more or less acute, sometimes with a split appearance and mostly irregularly crenulate edges; numerous isolated warts and short ridges present; plage distally amyloid. Basidia 35-75 × 10-15 μm, subclavate to clavate, mostly 4-spored but 1- and 2-spored basidia also present, sometimes with granular or guttate contents; sterigmata 2.5-10 × 1-3 μm. Pleuromacrocystidia absent. Pleuropseudocystidia 4-9 μm diam., scattered to moderately abundant, emergent, irregularly cylindrical, somewhat tortuous, sometimes branched. Lamellar edge mostly sterile; cheiloleptocystidia 6-36 × 3-7 μm, subcylindrical, subfusiform or subclavate, hyaline or with granular contents, thin-walled. Hymenophoral trama heteromerous; sphaerocytes intermixed with often somewhat inflated hyphae; lactifers moderately abundant to abundant. Pileipellis a trichopalisade to palisade, rather thin, 40-90 μm thick, containing pale brown, intracellular pigmentation, cell walls thin or slightly thickened and refringent, often a thin mucus layer present; suprapellis composed of long and slender terminal elements, 6-60 × 2-6 μm, cylindrical, subfusiform, sometimes subclavate, sometimes septate, mostly recumbent to repent, also upright; subpellis composed of few layers of inflated cells and hyphal elements, 10-25 × 10-15 μm, isodiametrically or irregularly shaped. Stipitipellis a cutis or trichoderm, 30-80 μm thick, hyaline.
Habitat and distribution: Solitary on the soil in montane mid-elevation rainforest with Quercus, Lithocarpus, Castanopsis, Dipterocarpus or Pinus.
Material Examined: THAILAND, Chiang Mai Province, Doi Inthanon National Park, near junction of Highway 1009 and road to Mae Chem, N18°31.58' E098°29.64', 1703 m alt., rain forest dominated by Quercus sp., Lithocarpus echinops, and Castanopsis armata, 25/06/2004, Huyen T. Le 147, (= Verbeken-Walleyn 04/115) (holotypus CMU, isotype GENT, SFSU) – Chiang Mai Province, Doi Suthep-Pui National Park, Sangasahasri Lane to Huai Kok Ma village, on soil and leaves, N18°48.62' E98°54.60', 1145 m alt., primary montane forest with predominantly Castanopsis armata, Castanopsis sp., Schima wallichii and Lithocarpus polystachyus, 24/06/2005, leg. D. E. Desjardin, Huyen T. Le 310 (CMU, SFSU, GENT) – ibid., 21/07/2005, Huyen T. Le 355 (CMU, SFSU, GENT) – Chiang Mai Province, Doi Inthanon National Park, near 25 km marker along Highway 1009, N18°32' E098°33', 1076 m alt., rainforest dominated by Castanopsis armata and Pinus sp., 05/06/2005, Huyen T. Le 399 (CMU, GENT, SFSU) – Chiang Mai Province, Doi Inthanon National Park, near 22 km marker along Highway 1009, N18°32.54' E98°33.51', 1076 m alt., rainforest dominated by Castanopsis armata and Pinus kesiya, solitary on the soil, 27/06/2005, Huyen T. Le 325 (CMU, SFSU, GENT) – Chiang Mai Province, Mae Taeng Distr., near 22 km marker along Highway 1095, 750 m alt., N19°07.57' E98°45.65', forest dominated by Dipterocarpus spp. and Pinus kesiya, under Pinus sp., 04/06/2006, leg. R. Halling, Huyen T. Le 390 (CMU, SFSU, GENT).
Notes: In the field, L. friabilis might be confused with L. subplinthogalus var. chiangmaiensis due to the pale colours, the distant and broad lamellae, and the pink staining of the context. However, microscopically L. friabilis is easily distinguished by its reticulate spore ornamentation, whereas L. subplinthogalus var. chiangmaiensis has a distinctly zebroid ornamentation. In Huyen T. Le 325, cells with conspicuously thickened cell walls were observed in the pileipellis. However, these cells were equal in shape and size with the other pileipellis elements, and cells with intermediate cell wall thickness were present. We therefore do not consider them as true lamprocystidia. Similar thick-walled cells have been observed in Huyen T. Le 390, but in far lesser abundance. Pileipellis elements with refringent and slightly thickened cell walls were present in all specimens. Molecular analyses confirm all specimens belong to the same clade. Within this clade, Huyen T. Le 325 and Huyen T. Le 390 were persistently grouped together, apart from the other specimens. No other differing characters were found except the thick-walled pileipellis elements. Because this appears to be a variable character, we find it precarious to describe them as a separate taxon and consider the abundance of thick-walled pileipellis elements as part of the variability within the species.
Fig. 1 MP phylogeny of Lactarius subgenus Plinthogali in Northern Thailand based on ITS sequences. The 50% majority rule consensus tree resulting from the Maximum Parsimony analysis with the bootstrap values higher than 50% added on the internal nodes.
Fig. 2 Lactarius friabilis. a. basidiomes, b. basidiospores, c. basidia, d. cheiloleptocystidia, e. pleuropseudocystidia, g. pileipellis, h. stipitipellis. Scale bars = 10 mm (basidiomes) and 10 μm.
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