Agaricus longistipitatus R.L. Zhao & B. Cao, in Cao et al., Fungal Diversity 132: 504 (2025)
Index Fungorum number: IF 572241; MycoBank number: MB 572241; Facesoffungi number: FoF 17101; Figs. 1, 2
Etymology – refers to the species having a long stipe.
Holotype – HMAS 255764.
Pileus initially globose, then hemispherical, brown to dark brown, uplifted or appressed, squamose scales, more appressed and smaller at the center. Pileal surface dull, dry. Lamellae free, crowded, up to 0.6 cm broad, at first whitish, then reddish-brown, edge whitish. Stipe generally solitary, 14–26 × 2–4 cm, central, narrowly fistulose, cylindrical, progressively tapered towards the base, annulate in its upper part. Annulus superous, membranous, thick, smooth upper surface, fibrillose from the universal veil along the margin. Context first white, then reddish, slowly becoming reddish brown everywhere on exposure.
Basidiospores (5.8–)6.3–7.2–7.6 × (4.2–)4.7–5.8–6.4(–6.9) µm, Q = 1.16–1.25–1.35, ellipsoid to broadly ellipsoid, brown, thick-walled, without germ pore. Basidia 29.2–44.3 × 9.9–13.1 µm, clavate. Pleurocystidia absent. Cheilocystidia hyaline, often with a basal septum, the terminal element being clavate to cylindrical 19.7–36.4 × 7.7–10.5 µm. Pileipellis constituted by cylindrical, radially arranged hyphae, 3.9–10.8 µm wide, not or slightly constricted at septa.
Chemical reactions – Schäffer’s reaction positive.
Material examined – CHINA, Gansu Province, Wuwei City, Tibetan Autonomous County of Tianzhu, 22 August 2018, collected by An-Qi Liu, ZRL20181453 (HMAS 281410); 24 August 2018, Bin Cao, ZRL20181408 (HMAS 255764, holotype).
GenBank – HMAS 255764: PQ628228 (ITS); HMAS 281410: PQ628227 (ITS).
Notes – Neither of the two specimens of Agaricus longistipitatus had fully unfolded caps, preventing the observation of mature fruiting body morphology. The most notable characteristic of this species is its exceptionally long stipe, approximately 3/4 of which remains underground.
Figure 1 – Agaricus longistipitatus. a, b Basidiomata (HMAS 255764, holotype). c Basidiomata (HMAS 281410). d Basidiospores. e Basidia. f Cheilocystidia. g Pileipellis hyphae. Scale bars: a–c = 2 cm, d–g = 10 µm.
Figure 2 – Maximum Likelihood tree of Sect. Bivelares and Bohusia based on ITS sequences, bootstrap values greater than 50% are shown around nodes. New species are shown in blod. “T” refers to a type specimen.