Choiromyces mongolicus S.P. Wan & F.Q. Yu, in Cao et al., Fungal Diversity 132: 459 (2025)

Index Fungorum number: IF 852605; MycoBank number: MB 852605; Facesoffungi number: FoF 15541; Figs. 1, 2

Etymology – refers to Inner Mongolia Autonomous Region, the locality of the type specimen.

Holotype – YNAU1853.

Ascomata 2.4–10.5 cm in diam, hypogeous, subglobose or tuberiform, knobby with deep lobes, partially cracked, surface smooth, white, pale yellow to reddish brown with white crackles when fresh, then becoming reddish-brown when dry. Peridium 252–552 µm thick, not clearly differentiated, prosenchymatous, composed of subglobose to subangular cells, 4.3–15.2 × 3.9–11.9 µm, light brown or hyaline, and composed of intricately interwoven, hyaline and thin-walled hyphae, 4.0–6.4 in diam. Dermatocystidia, multi-septate, multinodal, branched, blunt-tipped, intertwining and forming dense and friable superficial layer, 0.7–10 µm at septa in diam, hyaline to whitish. Gleba solid, milky white, pale yellow to reddish brown with a light brown tinge, marbled with white veins, consisting of interwoven thin-walled hyphae. Odor strong mushroom flavor pleasant. Asci hyaline, clavate to saccate, 8-spored, (62.5–)70.9–99.6(–101.8) × (37.4–)37.5–56.0(–57.9) µm (n = 30). Ascospores spherical, pale yellow–brown at maturity, (16.9–)17.5–22.0(–23.1) × (16.5–)17.3–21.4(–22.6) µm in diam (n = 80), (Q = 1.00–1.06), ornamented with straight or slightly curved stick-like sparse spines, 1.20–1.96 µm tall, with irregularly blunt or rounded tips.

Material examined – CHINA, Inner Mongolia Autonomous Region, Xing’an League, 46°77’N 120°31’E, 1100 masl, 7 Oct 2023, WSP2645 (YNAU1853, holotype); Xing’an League, 46°76’N 120°33’E, 1108 m asl, 7 Oct 2023, WSP2641 (YNAU1849); Xing’an League, 46°80’N 120°33’E, 1108 m asl, 7 Oct 2023, WSP2642 (YNAU1850); Xing’an League, 46°80’N 120°41’E, 1204 m asl, 7 Oct 2023, WSP2643 (YNAU1851); Xing’an League, 46°80’N 120°44’E, 1211 m asl, 7 Oct 2023, WSP2644 (YNAU1852); Liaoning Province, Dalian City, Pulandian District, 39°38’N 122°03’E, 876 m asl, 14 Sep 2023, WSP2613 (YNAU1821).

GenBank – YNAU1853: OR840536 (ITS); YNAU1849: OR840532 (ITS); YNAU1850: OR840533 (ITS); YNAU1851: OR840534 (ITS); YNAU1852: OR840535 (ITS); YNAU1821: OR840531 (ITS).

Notes – Choiromyces mongolicus belongs to the Heilan shanensis group (Fig. 2). This group includes all Chinese species, and has been distinguished from other European, American and Asian taxa. Phylogenetically, C. mongolicus is clearly separated from the other three reported Chinese species, C. cerebriformis, C. helanshanensis and C. sichuanensis (Fig. 2). Moreover, there are distinct morphological differences, with C. mongolicus having typical one-layer peridium, and smaller spores up to 22.6 µm (Chen et al. 2016; Yuan et al. 2021; Wang et al. 2022).

Figure 1 – Choiromyces mongolicus (YNAU1853, holotype). a Ascoma. b Dermatocystidia. c Peridium section. d, e light micrograph (LM) of ascospores. f SEM image of an ascospore.

Figure 2 – Maximum Likelihood tree based on ITS sequences, bootstrap values greater than 50% and posterior probabilities greater than 0.90 are shown around nodes. New species are shown in red. “T” refers to a type specimen.