Tuber mixtecorum J. García, Ayala-Vásquez & de la Fuente, 2021

García-Jiménez, Jesús, Ayala-Vásquez, Olivia, Guevara-Guerrero, Gonzalo, Garza-Ocañas, Fortunato & Fuente, Javier Isaac De La, 2021, Tuber mixtecorum (Tuberaceae, Pezizales) a new truffle in the Maculatum clade from Mexico, Phytotaxa 509 (1), pp. 113-120 : 116-118

Tuber mixtecorum J. García, Ayala-Vásquez & de la Fuente , sp. nov. ( Fig. 2 ).

Mycobank no. MB 838344.

Type: — MEXICO. Oaxaca: Nochixtlán municipality, road to Apoala , 17°28’33” N, 97°12’21 “W, 2281 m.a.s.l., 19 August 2018, García 21880 (holotype ITCV [JGARCIA-21880- ITCV].

Diagnosis: — Tuber mixtecorum is characterized from other species in the Maculatum clade by the whitish to brownish grey peridium, composed of interwoven or postrate cells, with erect claviform terminal elements of 19–24 µm, ellipsoid ascospores of 15–33.9 × 11.3–23.3 µm and the putative association to Quercus castanea .

Description: — Ascocarps 3–16 × 3–13 mm, globular, subglobose, slightly hunched over, whitish or brownish gray in color (30A2), stains dark brown when handled, subtomentose, in some areas somewhat glabrous, dry texture, no rhizomorphs at the base. Peridium of less than <1 mm, without changes in color when cut, marbled gleba, blackish or dark violet color (18F5), with violet white veins (18A2), some of them ending in peridium. Fungoid smell, soft. Fungoid taste, oily.

Peridium of 173–239 µm in thickness. Outer layer 52–89 µm thick, formed by interwoven tubular or prosenchymal hyphae, 3–6 µm in diameter, with some loosely interwoven with emerging cytidioid elements, claviform or subclaviform, 19–24 µm long, hyaline in KOH, immutable in Melzer, without intracellular content, thick-walled. Internal layer 114– 138 µm thick, formed by interwoven hyphae or in some areas subglobose hyphae, or rarely prostrate, 4–9 µm wide, hyaline, without intracellular content, smooth and thin walled. Vein hyphae 4–9.6 µm in diameter, tubular, hyaline in KOH, yellowish in Melzer, with septa, without content, smooth and thin walled. Ascospores subglobose to ellipsoid of 15–33.9 × 11.3–23.3 µm without ornamentation, alveoli 2–4 µm long, polygonal (4–7) isodiametric, 4–8 alveoli lengthwise, 3–5 widthwise, brown to pale brown, thick wall up to 3 µm. Monosporic asci have spores of 25.7–33.9 × 14.2–23.3 µm; bisporic asci have spores of 21.9–28.5 × 14.2–19.5 µm; trisporic asci have spores of 12.1–24.8 × 12–15.6 µm; tetrasporic asci have spores of 15–17.6 × 12.6–14.6 µm; pentasporic asci have spores of 19.3–21.9 × 11.5–13 µm. Asci of 53.7–65.8 × 32–56.8 µm subglobose, ellipsoid, some ovate, thick-walled, hyaline in KOH, yellowish in Melzer, without pedicel.

Etymology: —Named mixtecorum in reference to the mixteca zone, where this species was discovered.

Distribution: —Known from the Mexican state of Oaxaca, growing hypogeous or semi hypogeous in Quercus- Pinus dry mixed forest under Quercus castanea .

Comments: —This new species is characterized from other species within the Maculatum clade by the whitish, subtomentous peridium, with short ellipsoid spores of 15.0–33.9 × 11.3–3.3 µm. It is similar to Tuber maculatum described by Pegler et al. (1993) in Europe and Cazares et al. (1991) from Mexico by the prosenquimatous structure of the peridium and claviform cystidioid elements, however, the material described by Cazares et al. (1991) has longer spores (40–80 × 40–54 µm) while the European material has wider spores (25–55 × 21–40 µm). This species has the shortest spores within the northamerican species of the Maculatum group ( Table 2). Another significant difference is the absence of flat or pyramidal warts present in other species of the group (Guevara-Guerrero et al. 2013). T. lauryi (2013: 203) can also present a smooth looking peridium, however, it is easily separated from T. mixtecorum by having larger spores (22–50 × 20–41 µm) and its association with Quercus garryana and Pseudotsuga menziesii (Guevara- Guerrero et al. 2013). Morphologically it is similar to T. tequilanum Guevara, Bonito & Trappe (2015: 370) in the whitish ascocarps, thickness and cystidioid elements of peridium but it differs in spore size being the longer in T. tequilanum (up to 55 µm), the ecological habit under Quercus magnoliifolia in humid pine-oak forests and that this species belongs to the Puberulum clade (Guevara-Guerrero et al. 2015, Gómez-Reyes et al. 2018).

Figures

FIGURE 2. Tuber mixtecorum (Holotype). A. Details of the gleba. B. Ascospore showing the alveolate ornamentation. C. Asci and ascospores. D–E. Details of the terminal elements of the peridium. Scale bar: 10 mm (A); 20 µm (B–E).