Russula luteonana M. Pobkwamsuk & K. Wisitrassameewong
Mycobank: MB 840550
Pileus medium-sized, 28‒53 mm diam., plano-convex with depressed centre, infundibuliform when mature; margin striated and radially cracking in dry condition; cuticle dry, peeling to almost ½ of radius, smooth to minutely wrinkled, dull in dry condition, color very variable, some collections pale cream and with darker pale brownish-yellow centre, other yellow brownish and with darker orange-brown centre, sometimes also bright red-brown and with discolored centre, always with rusty-brown spots especially when near the centre. Lamellae: 3‒5 mm deep, moderately distant, intervenose, forking near the stipe, white to cream, edges even, concolorous. Stipe: 26‒40 × 6‒9 mm, cylindrical or narrowed at the base, surface dry, longitudinally wrinkled, white, turning brown when bruised. Context: 2‒4 mm in at the half pileus radius, soft, solid, becoming partially hollow when mature, white, unchanging when cut. Taste mild; odour rather strong, fishy. Spore print: not observed.
Spores (7.4‒)8.1‒8.6‒9(‒10.1) × (6.1‒)7.4‒7.5‒7.9(‒9.1) μm, subglobose to broadly ellipsoid, Q = (1.03‒)1.09‒1.15‒1.20(‒1.30), ornamentation of moderately distant, obtuse, (0.7‒)1.1‒1.3‒1.5(‒1.9) μm high spines, connected by abundant line connections [(0‒)3‒6(‒8) in in a 3 µm diam. circle], branched, forming an incomplete reticulum, crest irregularly wavy and occasionally fused [(0‒)1‒2(‒5) fusions in the circle], isolated elements rare; suprahilar spot inamyloid. Basidia: (29‒)34.5‒39.1‒44(‒51.5) × (10‒)12‒13.2‒14.5(‒16.5) μm, clavate, 4-spored, rarely 2-spored, basidiola subcylindrical to subclavate, (25.5‒)30‒35.4‒41(‒47) × (9‒)11‒12.2‒14 (‒16) μm. Hymenial cystidia on lamellae sides: usually protruding over other elements of hymenium, widely dispersed (< 350/mm2), (65‒)78‒92.1‒106.5(‒132) × (10.5‒)14‒17.4‒21(‒24) μm, fusiform to lageniform, apically obtuse to subacute, thin- or slightly thick-walled; contents homogenous, optically empty, negative in sulfovanillin. Lamellar edges: with dispersed basidia; Marginal cells: very abundant, mainly long and apically acute, resembling terminal cells in the pileipellis, (28.5‒)41.5‒55‒69(‒93) × (5.5‒)7.5‒9.0‒10.5(‒13) μm, fusiform, rarely lanceolate or lageniform, often fasciculate; mixed with less frequent, distinctly shorter, broadly clavate or obpyriform elements μm, (12.4‒)20.1‒25.7‒31.2(‒44.0) × (5.2‒)‒8.9‒10.9‒12.8(‒14.8) μm. Pileipellis: (Fig. 10) orthochromatic in Cresyl blue, sharply delimited from the underlying context, 110‒350 um deep; suprapellis a trichoderm of ascending or erect hyphal terminations, non-gelatinized, subpellis composed of dense, strongly gelatinized, horizontally oriented, narrow hyphae. Acid-resistant incrustations: absent. Hyphal terminations near the pileus margin: mainly unbranched, apically often flexuous, usually composed of distinctly longer terminal cells and a single subterminal short cells, thin-walled; terminal cells of two distinct types, either long and apically attenuated or short, subcylindrical and obtuse, constricted on septa, the long type (27.5‒)44.5‒60.7‒76.5(‒100.5) × (4.0‒)5‒6.6‒8(‒11.3) μm, subulate, narrowly fusiform or narrowly lageniform, apically acute ; the short type (16.4‒)24.7‒36.2‒47.8(‒71.9) × (3.7‒)4.7‒5.7‒6.8(‒7.7) μm, cylindrical, rarely narrowly clavate or somewhat apically narrowed, occasionally moniliform; subterminal cells shorter, mainly unbranched, 5‒8 μm wide. Hyphal terminations near the pileus centre: similarly with terminal elements of two types, the longer type (20‒)37.5‒53‒69(‒90) × (3.5‒)5‒6.1‒7.5(‒9) μm, subulate and acute or subcylindrical and obtuse, the shorter type (12‒)18.5‒31.4‒44.5(‒65.5) × (3‒)4‒5.0‒6(‒7) μm, subcylindrical, cylindrical, rarely narrowly clavate. Primordial hyphae or pileocystidia: absent. Cystidioid hyphae and oleipherous hyphae: in subpellis absent.
Specimens examined: THAILAND, Amnat Charoen province, Hua Taphan district, Junction near Watbochaneng, dry dipterocarp forest, 13 July 2016, 3 collections from different mycelia at this site, Thitiya Boonpratuang, Rattaket Choeyklin, Prapapan Sawhasan, Maneerat Pobkwamsuk, Pattrachai Juthamas, Nattawut Wiriyathanawudhiwong, Patcharee Patangwesa, (BBH41121, BBH41122, BBH41125); ibid., 29 May 2017, Thitiya Boonpratuang, Rattaket Choeyklin, Maneerat Pobkwamsuk, Nattawut Wiriyathanawudhiwong, Tuksaporn Thummarukcharoen (BBH42510).
Notes: Russula luteonana is extremely variable but based on the pileus colour we can eliminate some species with purple or green tints. If we combine this with the white or nearly so stipe, it can only be confused with either R. bella (if it has redder colouration) or R. orientipurpurea. The unique character of R. luteonana is the large cystidia which range 14–21 μm in width and are often also obtuse. While R. bella has many microscopic characters that distinguish it from this proposed species (e.g. smaller spores, narrower hymenial cystidia), R. orientipurpurea resembles, in many aspects, the Thai species (i.e. relatively large spores, obtuse and relatively wide hymenial cystidia on the lamellae sides, and usually only one unbranched short cell below the terminal cell of hyphae in pileipellis). Distinguishing features of these two species are the more prominent spore ornamentations and the often acute hymenial cystidia of R. luteonana.
Fig 1. ML phylogenetic tree inferred from the three-gene dataset (ITS, rpb2, mtSSU) of Russula subsection Amoeninae species, using ML and BI analyses. Three members of R. subg. Heterophyllidiae are used as outgroup. Species in boldface are new species in this study. Bootstrap support values (BS ≥ 50%) and posterior probabilities (PP ≥ 0.90) are shown at the supported branches.
Fig 2. Basidiomata of Russula luteonana. (A) BBH41120 (Holotype). (B) BBH41121. (C) BBH41122. (D) BBH42510. Scale bar = 1 cm. Photos by Thitiya Boonpratuang.
Fig 3. Hymenial elements of Russula luteonana (holotype, BBH41120). (A) Spores as seen in Melzer’s reagent. (B) Clavate marginal cells. (C) Subulate marginal cells. (D) Basidia. (E) Hymenial cystidia on lamellae sides. Scale bar = 10 µm.
Wisitrassameewong K, Manz C, Hampe F, Looney BP, Boonpratuang T, Verbeken A, Thummarukcharoen T, Apichitnaranon T, Pobkwamsuk M, Caboň M, Adamčík S. 2022 – Two new Russula species (fungi) from dry dipterocarp forest in Thailand suggest niche specialization to this habitat type. Scientific reports. 18;12(1):1-5.
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