Tuber incognitum Pina Paez , Bonito, Guevara & Castellano

Paez, Carolina Pina, Bonito, Gregory M., Guevara-Guerrero, Gonzalo, Castellano, Michael A., Garibay-Orijel, Roberto, Trappe, James M. & Ramirez, Rafael Pena, 2018, Description and distribution of Tuberincognitum sp. nov. and Tuberanniae in the Transmexican Volcanic Belt, MycoKeys 41, pp. 17-27 : 18-19

Tuber incognitum Pina Paez, Bonito, Guevara & Castellano sp. nov. Fig. 1 a–d

Type.

MÉXICO, State of Querétaro, Huimilpan, San Pedro, under Quercus crassifolia Humb. and Bonpl., Quercus spp., hypogeous, gregarious, 24 September 1996, M.A. Castellano (Holotype: OSC 150066), GB GQ221447. State of Michoacán, Zinapécuaro, el Jaral, under Quercus polymorpha Schltdl. and Cham., hypogeous, solitary or in groups of two, 2380 m alt., 19°46'48"N, - 100°47'24"W, 4 September 2008, R. Garibay-Orijel (Paratype: MEXU 25995), GB KJ595014. State of México, Temascaltepec, under Quercus spp., hypogeous, solitary, 2011 m alt., 19°04'12"N, - 100°01'48"W, 8 July 2009, R. Garibay-Orijel (Paratype: MEXU 26218), GB KJ595013.

Diagnosis.

Tuber incognitum is distinctive in the structure of its peridium (two-layered) and spore size (25-55 × 20-44 μm), which separates it from the rest of the species within the Puberulum clade reported from México.

Etymology.

Incognitum is Latin for unknown. The name incognitum is not derived from its morphology, rather from the fact that it was overlooked for so long. The holotype was collected in 1996 and not described until now.

Description.

Ascomata 10-15 mm broad, subglobose to slightly irregular, white with light brown areas when dry, glabrous, with canals that continue with the veins into the gleba. Gleba pinkish to purplish pale-brown in youth, dark brown at maturity, marbled with white veins. Odour fruity, pleasant.

Peridium two-layered, when handled the upper layer is lost and only the inner layer is observable under the light microscope, 350-400 μm thick, pellis 175-240 μm thick, composed of isodiametric or angular cells, 6-15 μm broad, walls 1.75-2.0 µm thick, yellowish hyaline in KOH. Subpellis 110-140 µm thick, composed of septate, interwoven hyphae (textura intricata), 4.5-7.0 µm broad, thin walled <1 μm thick, hyaline in KOH. Gleba composed of septate, interwoven hyphae (textura epidermoidea), 5.0-7.5 µm broad, thin walled <1 μm thick, hyaline in KOH. Ascospores broadly ellipsoid; excluding their alveolate-reticulate ornamentation, in 1-spored asci 45-55 × 34-44 μm (Q = 1.3), 2-spored 37-43 × 29-34 μm (Q = 1.25-1.36), 3-spored 30-42 × 26-31 μm (Q = 1.2-1.37), 4-spored 28-33 × 24-28 μm (Q = 1.09-1.25) and 5-spored 25-28 × 20-28 μm (Q = 1.2-1.25), spore colour orange-yellow in KOH, the walls> 2 μm thick; reticulum with 3-8 alveolae across the spore surface; the alveolar walls 3.5-4.0 μm tall. Asci globose, subglobose to broadly ellipsoid, pyriform, 88-100 × 70-95 μm, pedicel lacking to prominent, hyaline in KOH, hyphae around the asci prostrated or interwoven, cylindrical, 3.5-6.0 μm broad at the septa, thin walled, hyaline in KOH.

Distribution and ecology.

Only known from central and southwest México ( Querétaro, Michoacán, State of México, Guanajuato and Hidalgo). Ascocarps always associated with Quercus species ( Q. crassifolia , Q. polymorpha ). An EcM association with Quercus has been verified (MH174661) and its DNA has been recovered only from soil in Quercus forest in Hidalgo, México.

Additional collections examined.

MÉXICO, State of Guanajuato, Guanajuato, Las Palomas, under Quercus spp., hypogeous, in groups of two, 2534 m alt., 21°03'50"N, - 101°13'23"W, 10 October 2016, R. Peña-Ramirez (ITCV 1695).

Taxonomic comments.

Tuber incognitum resembles Tuber pseudoseparans in the colour of the peridium and the lack of dermatocystidia but differs by the size of the spores (being smaller in T. incognitum , 31-50 × 24-37 μm vs. T. pseudoseparans , 46-65 × 34-46 μm) and in the thickness of the peridium (being thinner in T. pseudoseparans , by ± 250 μm). Tuber incognitum is similar to Tuber bonitoi in spore size and ornamentation, but differs by the presence of dermatocystidia, which are absent in T. incognitum and the thickness of the peridium, being thicker in T. bonitoi (200-500 μm). Tuber incognitum is similar to Tuber guzmanii in the peridial organisation, both species have a well differentiated two-layered peridium but differ in the thickness (being thinner in T. guzmanii , 100-160 μm) and spore ornamentation (alveolate reticulum, 2-4 μm tall) and the size of the spores (being larger in T. guzmanii , 27-68 × 30-50 μm). The collection from Guanajuato represents a young developmental stage of T. incognitum , this collection has a thinner peridium (130-345 μm) and smaller spores (1-spored asci 23-35 × 19-25 μm, Q = 1.09 1.59; 2-spored 18-29 × 17-22 μm, Q = 1.0-1.61; 3-spored 30-42 × 26-31 μm, Q = 1.11-1.2; 4-spored 23-27 × 19-25 μm, Q = 1.08-1.26). These differences represent morphological variation within the species and its identity was confirmed with molecular data.