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 Add this item to the list  822054 Original description
Remarks (public):This is a member of L. sect. Pallidini Bon & Basso. In subalpine-alpine regions of southwestern China, L. castaneus W.F. Chiu, L. olivaceogelutinus K. Das & Verbeken and this new species formed a species complex, closely related to North American species of L. stirps Mucidus and European species of L. sect. Pallidini, e.g. L. albocaneus and L. hysginus. All these species have a glutinous pileus (and even stipe), an ixotrichoderm as the pileipellis and relatively big basidiospores and macrocystidia. ITS sequences of these species (Table 1) are also highly similar (similarity 96%–99%). Lactarius purpureocastaneus combines the reticulate basidiospores of L. castaneus (Chiu 1945; Wang 2007) with the darker pileus of L. olivaceoglutinus [based on the descritpion given by Das et al. (2015) and the author’s observations on Chinese specimens]. Microscopically the only reliable difference between L. castaneus and L. purpureocastaneus is the presence of brownish extracellular encrustations in the pileipellis of L. purpureocastaneus.
By the dark-colored pileus with encrustations and big basidiospores with clean reticulum, this species resembles North American L. caespitosus and L. kauffmanii Hesler & A.H. Sm. Basidiospores of L. caespitosus have lower ornamentation (0.2–0.5m) and its latex stains lamellae yellow (Hesler & Smith 1979). Lactarius kauffmanii has even darker pileus (“blackish-brown”) and vinaceous lamellae (Hesler & Smith 1979).
Description type:Original description 
Description:Basidiocarps medium-sized. Pilei 4–8cm, convex with slightly inrolled margin; surface greasy to glutinous, brownish orange to brown (5C3, 6E4) with more or less purplish tinge, sometimes mixed with olivaceous tinge, often with paler patches; margin glabrous, concolorous with or paler than the center. Context 3–4mm thick, white. Lamellae 2–7mm broad, straight to short decurrent, subcrowded to crowded, sometimg forking near the stipe, white to yellowish white (4A2) when young, pale yellow (4A3) to yellowish brown when mature. Stipes 3–9.5× 1–1.7cm, equal or tapering upwards, central, rarely eccentraical, solid; surface sometimes with pits, greasy, paler than the pileus; base sometimes strigose. Latex copious, white, discoloring glaucescens when dry, very acrid. Basidiospores (120/6/4) (8.0) 9.0–11.5(12.5)× 7.0–9.0(10.0)m [Q=(1.13)1.17–1.33(1.39), Q= 1.23±0.05] [holotype: (8.0) 8.5–10.5 (12.0)×7.0–8.5 (9.5)m [Q=(1.14)1.18–1.36(1.37), Q=1.25±0.05], broadly ellipsoid to ellipsoid; ornamentation 0.5–1.0(1.3)m high, of regular ridges connected into an incomplete to complete clean reticulum, some ridges aligned in a zebroid pattern, isolate warts and free ends of ridges present; plage not or distally amyloid. Basidia 50–60×12–15m, 4-spored. Pleuromacrocystidia common to abundant, 80–120× 9–15m, emergent, projecting 30–50m beyond the basidia-layer, lanceolate with an acute or moniliform apex, with a yellowish content at the apex or in the whole cystidia. Pseudocystidia uncommon, 3–4m broad, cylindrical. Lamella edge sterile or fertile; cheilomacrocystidia common, 60–80×7–10m, subfusiform or subcylindrical with a acute or blunt apex. Pileipellis a persistent ixotrichoderm, 200–500m thick, with an hyphae-free outmost slime-layer 20–300m thick; hyphae 2–4m broad in suprapellis and 4–7(10)m broad in subpellis; brownish encrustations scattered to abundant, often coating the hyphae in the subpellis or context. Stipitipellis an ixocutis, 30–100m thick; hyphae 2–4m broad, densely interwoven, gelatinized, sometimes with brownish encrustations. 
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