Clitopaxillus alexandri (Gillet) G. Moreno, Vizzini, Consiglio & P. Alvarado, in Alvarado et al., Fungal Diversity. 90:109-133 (2018)
Pileus first convex, flattened with age, with a central umbo, grayish brown to reddish yellow, with margin enrolled, measuring (5–)10–15(–20) cm in diam., smooth, somewhat guttulated and finally cracked. Lamellae arcuate to decurrent, pale brownish grey to yellowish, subconcolorous. Stipe 4–10 x 2–4(–5) cm, solid, cylindrical, yellowish white to pale yellow. Context whitish, dense. Smell cyanic (i.e., bitter almonds).
Basidiospores 4.7–5.5 x 3.5–3.9 µm (n = 32), (average 5.1 9 3.7 µm), Q = 1.27–1.49 (Qm = 1.38); Vm = 36 µm3, broadly ellipsoid to ellipsoid in front view, slightly amygdaliform to larmiform in side view, hyaline; hilar appendix often very pronounced, 0.8–1 µm long; in Melzer’s spore wall stains bluish-gray. Basidia 26–31 x 4.9–5.8 µm, four-spored, a few two-spored, long clavate to subcylindrical, sterigmata up to 5 lm long. Hymenophoral trama subregular, composed of hyphae up to 12 µm wide, hyaline in alkaline latex L4, yellow in Melzer’s. Cheilocystidia and pleurocystidia not observed. Pileipellis a trichocutis of variously intertwined, very loose, slightly gelatinized, filamentous hyphae, 3.0–6.3 µm wide, smooth, with intracellular brownish pigment, sometimes with a very fine encrusting epiparietal pigment. Pileitrama hyphae cylindrical, up to 12.6 µm wide, thromboplerous hyphae rare and inconspicuous. Clamp connections present at all septa of the subhymenial hyphae and at the base of basidia and basidioles, occasionally verticillate or unclosed (‘‘false clamps’’), scattered in mycelium, absent elsewhere.
Habitat: mediterraneo-atlantic, found in deep litter under pines (P. halepensis, P. pinea, P. sylvestris, P. uncinata) and oaks (Quercus ilex, Q. pubescens, etc.), along the Atlantic coasts, also with Cedrus atlantica in North Africa. Mediterranean basin and Central Europe.
Index Fungorum number: IF823304
Notes: No original or topotypical collection of C. alexandri could be traced, but the original locality near Alençon (western France), in a hilly area under Atlantic climate, matches the species described here, rather than the boreo-alpine lineage described below as C. fibulatus. No typification of C. alexandri is proposed at this time, in expectation of collections found around the original locality. Singer (1961) studied original material of Agaricus propinquus var. spadiceus Pers. and concluded that this taxon could be a synonym of C. alexandri, but he could not check any specimen of A. propinquus Pers. var. propinquus (synonymized to A. vinosus Bull.: Fr., Fries 1832), avoiding any nomenclatural change. Paxillus extenuatus Fr., not interpreted in modern taxonomy, has also been applied to C. alexandri, for instance by Ricken (1915), but Fries (1838) described its pileus as umbonate at first and a base ‘‘tuberoso-radicato’’, two features recalling A. vinosus Bull. cited above (Bulliard 1782: tab. 54) and incompatible with any species of Clitopaxillus known.