Clitopilus amygdaliformis Zhu L. Yang.
Basidiomata clitocyboid, usually medium- sized to large. Pileus 20–80 (110) mm wide, convex to plano-convex, often slightly depressed at center; surface whitish (1A1) to chalk white (4A1), slightly viscid when wet, glabrous; margin incurved, then straight, sometimes undulate; context 3–5 mm thick, whitish (3A1) or chalk white (4A1). Lamellae decurrent, yellowish white (4A2) to slightly yellowish pink (3A2), somewhat crowded to crowded, edges entire and concolorous, lamellulae numerous. Stipe 30–40 × 5–7 mm, usually eccentric, subcylindrical, concolorous with pileus, smooth; the base sometimes with white (1A1) mycelium. Odor farinaceous.
Basidiospores (7–)8–12(–13) × 5–7 μm, Lm × Wm = 9.44 (± 0.99) × 6.16 (± 0.42) μm, Q = (1.13–)1.24–2.08 (–2.17) (Qavg = 1.54 ± 0.17) [68/3/3], nearly hyaline, amygdaliform to limoniform and sometimes subovoid in profile and face view, angled in polar view with 5–6 obvious longitudinal ridges. Basidia 22–30 × 9–11 μm, clavate, hyaline, 4-spored, rarely 1- or 2-spored; sterigmata 1.5–4 μm long. Lamellar trama more or less regular, composed of 4–10 μm wide, hyaline hyphae; oleiferous hyphae rare; subhymenium consisting of filamentous hyphal segments. Lamellae edges fertile. Pleurocystidia and cheilocystidia absent. Pileipellis a cutis composed of more or less radially arranged, repent, hyaline, smooth, cylindrical hyphae, 2.5–6 μm wide; subcutis made up of irregularly and somewhat loosely arranged, thin-walled, hyaline, smooth, cylindrical hyphae, 3–6 μm wide; pileal trama composed of subregular, hyaline, cylindrical, inflated hyphae, 5–20 μm wide. Stipitipellis a cutis composed of compactly arranged, sometimes branched, thin-walled, hyaline hyphae, 3–5 μm wide. Caulocystidia absent. Clamp connections absent. Ecology and distribution: Single, scattered, or in groups on soil in conifer (viz., Picea, Abies) or broadleaved (viz., Quercus) forest, reported from Yunnan and
Taiwan, Jul to Sep.
Specimens examined: CHINA. YUNNAN PROVINCE: Baoshan City, Bawan, alt. 2100 m, 17 Jul 2003, L.F. Zhang 187 (holotype KUNHKAS42473); Diqing Tibetan Autonomous Prefecture, Shangri-La, alt. 3300 m, 21 Aug 2014, Q. Zhao 2184 (KUN-HKAS87950); Weixi Lisu Autonomous County, Tacheng Town, Bazhu Hamlet, alt. 2600 m, 8 Sep 2008, X.H. Wang 2256 (KUN-HKAS60406).
Notes: Clitopilus amygdaliformis is characterized by the whitish to chalk white, medium-sized to large basidioma with an eccentric stipe, the absence of hymenial cystidia, and broadly amygdaliform to limoniform basidiospores with 5–6 prominent longitudinal ridges. The holotype (KUN-HKAS42473) of C. amygdaliformis; however, it is infected by mold and only basidiospores could be observed. The basidiospores are unique in C. sect. Clitopilus such that this species can be recognized easily based on this feature alone. The somewhat loosely arranged hyphae of the pileipellis are also different from those of other species. Fortunately, we have re-collected this species and obtained DNA sequences of it, which establish a broad distribution including tropical areas and the subalpine. To fix the concept of this species, we have designated an epitype characterized by multiple DNA sequences.
Fig 1. Phylogenetic relationships among representative specimens of Clitopilus, Clitocella, and Clitopilopsis inferred from a multigene (28S, rpb2, tef1, and atp6) data set using both ML and BI methods (only the ML tree is shown). Bootstrap frequencies (>50%) and posterior probabilities (PP > 0.90) are shown on the supported branches. Sequences from type collections are marked, and altitude information of most specimens from KUN-HKAS is shown in the phylogram. New taxa are highlighted in red.