Lactarius formosus H.T. Le & A.Verbeken.
Pileus 27 mm diam., plano-convex with slight central depression and a very small papilla; surface viscid, zonate, scaly, covered with bundles of glutinous hairs, greyish yellow to yellowish buff with some olivaceous tones, changing quickly to dark purple (14F4) when bruised or broken; margin hairy. Lamellae subdecurrent, close to crowded, up to 1 mm broad, with 3 series of lamellulae, yellowish white (4A2), becoming dark ruby (12F4) when bruised or broken; edge dark purple (14F5). Stipe 40 × 6 mm, tapering upwards, central, greasy to dry, scrobiculate, yellowish white (4A2) at apex, concolourous with pileus, quickly changing to dark purple (14EF5) when bruised. Context 2.5 mm thick in pileus, greyish white to purplish white (14A2), hollow in stipe, pale yellow (3A3) with KOH 10%, dull yellow (3B3) with FeSO4; smell distinct; taste mild. Latex cream to yellowish white (4A2), staining the lamellae dark purple, pale yellow (3A3) to brownish orange (5C4) with KOH 10%. Spore deposit unknown. Basidiospores 8–9.7–11.3 (11.6) × 7.4–8.8–10.1 μm, (n = 20, Q = 1.01–1.1–1.38), globose to ellipsoid; ornamentation up to 0.6 (–1.6) μm high, composed of rather broad ridges, forming a mostly complete reticulum; plage inamyloid. Basidia abundant, 48–77 × 13–18 μm, with sterigmata 2–7 μm long, 4-spored, hyaline, sometimes with granular and guttate contents, thin-walled, subclavate. Pleuromacrocystidia abundant, 35–90 × 8–13 μm, emergent, subfusiform, with a mucronate to moliniform apex, hyaline or with granular contents, thin-walled. Pleuropseudocystidia not abundant, 8–11 μm wide, emergent up to 30 μm, tortuous to cylindrical, with lactiferous contents, thin-walled. Hymenophoral trama composed of filamentous hyphae. Lamellae edge sterile; marginal cells 11–21 × 3.5–7 μm, abundant, hyaline, 1-septate, cylindrical, thin-walled; cheilocystidia 29–60 × 8–9 μm, hyaline, subfusiform, similar to pleuromacrocystidia but smaller, with mucronate to moliniform apex. Pileipellis a cutis to a trichoderm, 120–140 μm thick; underlying layer composed of thin-walled filamentous hyphae and sphaerocytes. Stipitipellis a trichoderm, 90–130 μm thick composed of thin-walled hyphae; underlying layer composed of sphaerocytes and filamentous thin-walled hyphae.
Habitat and distribution: solitary in the soil among leaves near Pinus kesiya and Castanopsis armata.
Material examined: THAILAND, Chiang Mai Prov., Mae Taeng Dist., Tung Joaw village, N19°08.07' E098°38.09', 1423 m alt., rainforest dominated by Castanopsis armata and Pinus kesiya, 16 October 2005, leg. Huyen T. Le 382 (holotype CMU; isotype GENT, SFSU).
Notes: The species is striking in the field because of the quick colour change to violet in all parts combined with a hairy, viscid, zonate pileus and a scrobiculate stipe. The species is similar to the European L. repraesentaneus Britzelm. And the North American L. speciosus Burl., two species with violet staining latex that also share the hairy pileus with bearded margin and a scrobiculate stipe. The spore ornamentation of this new Asian species is very different from both temperate species. L. speciosus has spinose warts and ridges hardly forming a reticulum, while L. repraesentaneus has a denser but lower incomplete to complete reticulum. In the field L. formosus differs by the much smaller and slenderer basidiomes while the temperate species are both robust and larger. Since only one specimen has been found up to now, we do not know whether this is a consistent differentiating character. The colour of the basidiome is bright yellow in L. repraesentaneus and pinkish buff to cinnamon buff in L. speciosus. L. repraesentaneus is recorded from China by Wang and Xie (1984) and from Japan by Nagasawa (1998) and Imazeki et al. (1988), but on the basis of the colour picture of the latter, which shows an upside-down specimen only, it is hard to judge whether it represents the same taxon as ours. Molecular data indicates that L. formosus differs clearly from L. repraesentaneus and from L. speciosus. These three morphologically very similar species do not always form one clade. Whether L. formosus indeed belongs to subgenus Piperites is not always clear in the molecular phylogenies (see under general discussion). Its exact position needs a more thorough molecular approach based on more specimens.
Fig.1 Lactarius formosus. a. Basidiocarp. b. Spores. c. Basidia. d. Pleuromacrocystidia. e. Marginal cells. f. Pleuropseudocystidia. Scale bars = 10 mm (basidiocarp) and 10 μm.