Hygrocybe minimiholatra Ralaiv., Liimat., A.M. Ainsw., Niskanen sp. nov.

Index Fungorum number: IF 902405; Mycobank number: MB 902405; Facesoffungi number: FoF 16066; Figs. 1a, 2a, 3a, 4a

Etymology – The name is derived from the Malagasy word holatra meaning a fungus and the Latin word minimus denoting the smallest size and refers to the very small size of the basidiomata.

Holotype –K-M000251949

Pileus 0.3–0.6 cm in diam., convex, with a small depression in the centre, red. Lamellae subdecurrent, subdistant, thick, pale red. Stipe 1–2 cm long, 0.5–1.5 mm thick at the apex, mostly red and then pale red at the base, cylindrical. Odour indistinct. Basidiospores 7–8×4–5.5 µm,±ellipsoi d,smooth, hyaline in Melzer’s. Basidia 17–38×5–8.5(–10) µm, sterigmata 2–5 µm long, clavate, (2-)4-spored, clamped. Ratio of basidial to basidiospore length<5. Lamellar trama regular. Pileipellis cutis, clamped, hyphae 2–4 µm wide. ITS sequence (GenBank OR785988, holotype) distinct from other sequenced members of Hygrocybe and close to a species from Zimbabwe (UDB025759) with interspecific difference>4% (20 indels and substitutions).

Habitat – Dry, deciduous, tropical forest, on sandy soil.

Distribution – So far only known from Madagascar.

Material examined – Madagascar. Mahajanga, Ankarafantsika National Park, tropical dry forest, 12 Feb 2017, J. Galan 000251949 (K-M, holotype), MAF17-033.

GenBank numbers – OR785988

Notes – A minute red species with ellipsoid spores (7–8×4–5.5 µm). It belongs to Hygrocybe subgenus Hygrocybe and has the typical characteristics of that subgenus: the mean ratio of basidial to basidiospore length is<5. In addition, the lamellar trama is regular and the basidia and spores are monomorphic. It differs from its closest species Hygrocybe from Zimbabwe with 20 indels and substitutions (>4% interspecific difference).

Figure 1 – Basidiomata of the Hygrocybe species: a Hygrocybe minimiholatra 000251949 (holotype, K-M), b Hygrocybe parviholatra 000251897 (holotype, K-M), c Hygrocybe mitsinjoensis 000251832 (holotype, K-M), d Hygrocybe solis 000251894 (holotype, K-M), e Hygrocybe solis 000252075 (K-M), f, g Hygrocybe vintsy 000252026 (K-M). Photographs a Javier Galan, b Paul Eguia, c Tuula Niskanen, d Paul Eguia, e Tuula Niskanen, f, g Meilinda Sulastri. Scale bar 1 cm

Figure 2 – Basidiospores Hygrocybe species in Melzer’s. a Hygrocybe minimiholatra (K-M000251949, holotype). b Hygrocybe mitsinjoensis (K-M000251832, holotype). c Hygrocybe parviholatra (K-M000251897, holotype). d Hygrocybe solis (K-M000251894, holotype). e Hygrocybe vintsy (K-M000252026, holotype). Photographs Anna Ralaiveloarisoa. Scale bar=10 µm

Figure 3 – Basidia of the species of the genus Hygrocybe in Melzer’s. a Hygrocybe minimiholatra (K-M000251949, holotype). b Hygrocybe mitsinjoensis (K-M000251832, holotype). c Hygrocybe parviholatra (K-M000251897, holotype). d Hygrocybe solis (K-M000251894, holotype). e Hygrocybe vintsy (K-M000252026, holotype). Photographs Anna Ralaiveloarisoa. Scale bar=10 µm

Figure 4 – Pileipellis of the species of the genus Hygrocybe in Melzer’s. a Hygrocybe minimiholatra (K-M000251949, holotype). b Hygrocybe mitsinjoensis (K-M000251832, holotype). c Hygrocybe parviholatra (K-M000251897, holotype). d Hygrocybe solis (K-M000252026, holotype). e Hygrocybe vintsy (K-M000251894, holotype). Photographs Anna Ralaiveloarisoa. Scale bar=10 µm