Russulales » Russulaceae » Lactarius

Lactarius oomsisiensis

Lactarius oomsisiensis Verbeken & Halling, Austr

Index Fungorum: IF491842

Pileus 50-110 mm diam., depressed to slightly infundibuliform with small papilla; margin irregularly wavy, sometimes reflexed; surface dry, strongly radially rugose but smoother towards the margin, mostly pale coffee-and-milk coloured, locally with a more orange tinge (5BC5), with very fine, darker spots, becoming brownish grey when older or bruised. Lamellae broadly adnate, distant (3–6 L+l/cm), up to 15 mm broad, brittle, with subtle venations between the lamellae, up to 4 lamellulae between 2 lamellae, orange brown (6D4/7); edge entire, concolourous. Stipe 50-70 × 10-16 mm, central, equal or tapering downwards and often slightly curved at the base, more or less cylindrical; surface smooth, dry, whitish, cream coloured, somewhat brownish pink when touched (5B3/4). Context thick, 4-9 mm thick at mid-radius in pileus, solid in stipe, cream coloured (4A2), slowly turning pale brownish orange or dirty pinkish (7B5/6, 7C7), especially just beneath the surface of the stipe, unchanging with 10% KOH or FeSO4; smell mild, unremarkable or faintly rancid; taste mild, sometimes slightly acrid. Latex abundant, white, drying somewhat cream-coloured; unchanging with 10% KOH. Spore print colour unknown. Basidiospores (5.6) 6–77.6–8.5 × (5.4)5.7–6.87.3–8.3 μm (Q = 1.01–1.021.04–1.11; n = 100), globose to subglobose; ornamentation amyloid, forming an incomplete reticulum, composed of irregular ridges; ridges up to 1.5-2.0 μm high, rather acute, often with more or less crenulate edges; abundant, small, isolated warts present; plage distally to almost totally amyloid. Basidia 40-60 × 10-16 μm, subclavate to clavate, 4-spored, contents often guttate; sterigmata 3-9 × 1.5-2.5 μm. Pleuromacrocystidia absent. Pleuropseudocystidia 3-8 μm diam., abundant to very abundant, mostly emergent, cylindrical and smooth or more or less tortuous and irregular, sometimes branching towards the top, with crystalline or guttate contents, thin-walled. Lamellar edge mostly sterile; cheiloleptocystidia 15-40 × 3-7 μm, cylindrical, subcylindrical to fusiform, thin-walled, hyaline. Hymenophoral trama heteromerous, composed of hyphae intermixed with sphaerocysts; lactifers abundant. Pileipellis a trichopalisade to palisade, 40-80 μm thick, containing brown, intracellular pigmentation in the upper layers; suprapellis composed of subcylindrical to subfusiform terminal elements, 15-30 × 2-7 μm, mostly recumbent or oblique, thin-walled; subpellis composed of inflated cells, often somewhat elongated, 5-14 μm diam., a few to several layers thick, thin-walled. Stipitipellis a trichoderm, 20-60 μm thick; hyphae 2.5-5 μm diam., hyaline; terminal elements 13-37 × 2.5-5 μm, subcylindrical to subfusiform, upright to recumbent, thin-walled, hyaline.

 

Habitat and distribution: Solitary on the soil in mixed forests dominated by Castanopsis and Pinus, often near Pinus. Reported from Papua New Guinea and Thailand.

 

Material Examined: THAILAND: Chiang Mai Province, Doi Inthanon National Park, along Highway 1009 at 25 km marker, N18°32.54' E098°33.51', 1076 m alt., rainforest dominated by Castanopsis armata and Pinus sp., 11/06/2004, Huyen T. Le 108 (CMU, SFSU, GENT) – ibid., 02/07/2004, Huyen T. Le 172 (CMU, SFSU, GENT) – ibid., 27/06/2005, leg.W. Noparat, Huyen T. Le 316 (CMU, SFSU, GENT) – ibid., 04/08/2005, leg. R. Zhao, Huyen T. Le 368 (CMU, SFSU, GENT) – Chiang Mai Province, Mae Teang Distr., Ban Pha Deng village, near Pathumikaram Temple, 1076m alt., forest dominated by Dipterocarpus spp. and Castanopsis armata, on the soil near Shorea sp., 22/06/2004, Huyen T. Le 122 (CMU, SFSU) (= Verbeken and Walleyn 04/055, GENT).

Notes: Both morphological and molecular data confirm the conspecificity of these Thai specimens with Lactarius oomsisiensis Verbeken & Halling, although with low bootstrap support (61%). This species was described originally from Papua New Guinea where it is associated with Lithocarpus. The distant and rather dark, orange brown lamellae contrasting with the whitish stipe and the pale brownish cap make this species easily recognizable in the field. Its lamellae are among the darkest in the genus Lactarius. Other characteristic features are the rugulose cap surface and the thick context that slowly turns pinkish upon exposure. Microscopic features are the spore ornamentation that forms an incomplete reticulum with ridges up to 2 μm high, the striking abundance of pseudocystidia, and the trichopalisade in the pileipellis. The Thai specimens differ from the specimens from Papua New Guinea because of their larger dimensions and a mostly mild taste of the latex and, microscopically, in having a trichoderm in the stipitipellis instead of a trichopalisade. We consider these differences as part of the infraspecific variability. In both countries L. oomsisiensis is found in lowland to midelevation rainforests, dominated by Dipterocarpaceae or Fagaceae. It is the first time L. oomsisiensis has been recorded outside Papua New Guinea, but since its current distribution spans the far ends of Southeast Asia, it would be expected that this species can be found in similar habitats all over the Malesian region.

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 oomsisiensis. a. basidiomes, b. basidiospores, c. basidia, d. cheiloleptocystidia, e. pleuropseudocystidia, g. pileipellis, h. stipitipellis. Scale bars = 10 mm (basidiomes) and 10 μm.

 

Reference

 

Le HT, Stubbe D, Verbeken A, Nuytinck J, Lumyong S, Desjardin DE. 2007 – Lactarius in Northern Thailand: 2. Lactarius subgenus Plinthogali. Fungal Diversity. 27(1): 61–94.

 

 

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Supported by 
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Project entitled:
“Total fungal diversity in a given forest area with implications towards species numbers, chemical diversity and biotechnology” (Grant no. N42A650547).

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