Xanthagaricus purpureosquamulosus Sysouph., Thongkl. and K.D. Hyde
Mycobank umbero: MB 833740; Facesoffungi number: FoF 07071
Pileus 4.5–10 mm, first paraboloid or hemispherical, expanding to convex, planoconvex, with or without low umbo, when young completely covered with crowded squamules, brownish-grey (9D2–3) to violet-brown (10D4–8), soon breaking up into greyishbrown (9E2, 9D3) to violet-brown (10E4) squamules, crowded around center or umbo and with radially arranged squamules toward the margin, on pale-violet to violet (17A3–7) background and paler when mature; margin incurved, with brownish-grey (9D2–3) to greyish-brown (9E2, 9D3) appendiculate triangular velar remnants. Lamellae, l = 3–4 series, free, 1.5–2 mm wide, white to yellowish-white (4A2), becoming yellowish-grey to greyishyellow (4B2–3) when mature, broadly ventricose, with white, smooth to slightly eroded margin. Stipe 15–30 × 1–1.5 mm, slender and tapering downwards, covered with white to yellowish-white (4A2) squamules at apex, bellow annulus with crowded squamules toward the base, greyish-yellow, greyish-brown to light-brown (6D3–5), on yellowish-white to pale-yellow (4A2–3) background, darker at base zone, with greyish-brown (7E3–4) squamules. Annulus attached to apical zone of stipe, with velar remnants and concolorous to those on pileus margin, sometimes fragile with age. Context white in pileus, up to 1 mm thick at center; hollow in stipe and concolorous with surface. Odor and taste not observed. Spore pint greyish-orange (5B3).
Basidiospores [50,2,2] 4.5–6 × 3.5–4 µm, avl × avw = 5.34 × 3.78 µm, Q = 1.3–1.5, avQ = 1.4, ellipsoid-ovoid in frontal view, ellipsoid in side-view, thick-walled, smooth, hyaline to pale-brown, without a germ pore. Basidia 10–12 × 5.5–7 µm, obovoid, short clavate to ellipsoid, thin-walled, hyaline, 4-spored. Pleurocystidia absent. Cheilocystidia 10–16 × 5–8 µm, short clavate to clavate, ellipsoid, some branched, slightly thick-walled, hyaline. Pileus covering an irregular epithelium composed of globose to subglobose (7.5–25 µm wide) cells in the upper layer, broadly ellipsoid to oblong cells (10–62 × 5–15 µm) in the lower layer, thin-walled, smooth, with pale-brown to brown parietal and intracellular pigments, with pale-brown to hyaline, up to 7 µm wide hyphae at base of the epithelial layers. Stipe covering an irregular epithelium same as on pileus. Clamp connections absent. Habitat and distribution: growing in small to large groups, saprotrophic on humusrich soil with dead leaves and wood under trees of Samanea saman or beside grassland; commonly found on Mae Fah Luang University Campus, Chiang Rai, Thailand.
Additional material examined: Thailand, Chiang Rai Province, Muang District, Mae Fah Luang University Campus, 26 October 2018, P. Sysouphanthong, PS2018-217 (MFL19-2356, paratype).
Notes: there are only two species of Xanthagaricus, which resemble X. purpureosquamulosus in pileus color. X. caeruleus Iqbal Hosen, T.H. Li and Z.P. Song, described from China has pale-lilac to grayish-lilac or grayish-violet squamules on a pale-grayish-lilac to violet white background, but it differs from X. purpureosquamulosus by having white lamellae, which turn light-blue or pastel blue to grayish and finally ink-blue or blackish blue. Based on the phylogenetic analysis of ITS and LSU sequence data, X. caeruleus is not closely related to X. purpureosquamulosus. The second species with similar colors is X. ianthinus Y. Li and F.J.Wang, also from China, which differs from X. purpureosquamulosus by having bluish-violet to violet, more or less violet-brown squamules, white velar remnants, and yellowish-white to light-pinkish-white (4A2) lamellae. It is not close to X. purpureosquamulosus either in the phylogenetic tree based on ITS and LSU sequences. Xanthagaricus thailandensis J. Kumla, N. Suwannarach, and S. Lumyong, recently described from Thailand, differs in the larger pileus (30-45 mm), and the pale-orange to grayish-orange, large squamules on the pileus. The phylogenetic analysis of the ITS and LSU sequences shows that X. purpureosquamulosus is closely related to a group of species with yellow to olive-brown squamules, viz. X. epipastus (Berk. and Broome) S. Hussain, known from Sri Lanka, X. pakistanicus Hussain, Afshan and Ahmad from Pakistan, and X. necopinatus.