Rhytidhysteron mesophilum Cobos-Villagran , R. Valenz., Hdz.-Rdz., Calvillo-Medina & Raymundo, 2021

Cobos-Villagran, Aurora, Valenzuela, Ricardo, Hernandez-Rodriguez, Cesar, Calvillo-Medina, Rosa Paulina, Villa-Tanaca, Lourdes, Mateo-Cid, Luz Elena, Perez-Valdespino, Abigail, Martinez-Gonzalez, Cesar Ramiro & Raymundo, Tania, 2021, Three new species of Rhytidhysteron (Dothideomycetes, Ascomycota) from Mexico, MycoKeys 83, pp. 123-144 : 123

Rhytidhysteron mesophilum Cobos-Villagran, R. Valenz., Hdz.-Rdz., Calvillo-Medina & Raymundo sp. nov.

Fig. 4

Diagnosis.

Differs from Rhytidhysteron rufulum by its green-yellowish pruina on the margins, size of asci (267-282 × 15.5-16 μm) and larger ascospores (40-44 × 12-14 μm).

Type.

Molango de Escamilla Municipality , Laguna Atezca, 20°48'32"N, - 98°44'52"W, 1281 m a.s.l., 01 June 2018, A. Trejo 74 (ENCB). GenBank: LSUMW9394461, ITSMZ056799 .

Etymology.

The epithet refers to the type of vegetation (mountain mesophilic forest) it was collected from.

Description.

Ascomata hysterothecial to apothecial, 2.5-4 mm long, 1.0-1.5 mm wide, 1.4-1.7 mm high, superficial or erumpent, gregarious, rarely solitary, with small hysterothecial ascomata, ellipsoid to oblong and black when young, then boat-shaped hysterothecia, with some constriction in the middle part, flexuous, open in apothecioid ascomata, dark green (30F3-4), dull green (30E3-4), greyish green (30E6-7), deep green (30D-E8) to yellowish green (30B-C8) when mature, forming small ascomata within disc in old specimens. Margin involute, perpendicularly striate, marks are not roughness, rather irregular slits, with yellowish green (30B-C8) pruina. Exciple integrated in two layers, the first carbonaceous, glabrous, green yellowish, 62.5-75 μm thick, in the middle part widening more (112.5-125 μm), composed of pseudoparenchymal cells of textura prismatica (iso-radiating cells), the second composed of cells hyaline, thin-walled. Pseudoparaphyses 2.0-2.5 μm up to 3.0 μm wide, filamentous, capitate, hyaline, without septa, branched towards the apex, enclosed in a gelatinous matrix, strongly anastomosed above the asci. Epithecium reddish orange (7B8) to orange red (8A8), becoming greyish magenta (13D6) in the presence of 10% KOH. Asci 267-282 × 15.5-16 μm, bitunicate, cylindrical, hyaline, uniseriate, octosporic, thick-walled, with a sinuous base. Ascospores (38-)40-44(-46) × 12-14 μm, (x̄= 44.2 × 13.6, n = 30), ellipsoidal to oblong, light brown in colour, with three transverse septa, constricted at the septa, with a thick and smooth wall.

Distribution.

Known from a single locality in Laguna de Atezca, Molango de Escamilla, Hidalgo, Mexico.

Ecology.

Dead stems in tropical cloud forest.

Specimens examined.

Mexico. Hidalgo, Molango de Escamilla Municipality, Laguna Atezca , 20°48'32"N, - 98°44'52"W, 1281 m a.s.l., 01 June 2018; C. Herrera 40 (ENCB), A. Cobos-Villagrán 1800 (ENCB) .

Notes.

Rhytidhysteron mesophilum is characterised by a dark green, dull green, greyish green, deep green to yellowish green hysterothecium, forming small ascomata within disc in old specimens. This fungus could be confused with R. esperanzae because both are found in tropical cloud forest (mesophilic forests) and have similar ascospores. However, R. mesophilum is distinguished by a reddish orange to orange red epithecium, while in R. esperanzae , the epithecium is dark green to black. R. mesophilum also resembles R. columbiense by the presence of a yellowish green (30B-C8) pruina in the margin, but the ascospores are larger (38-52 × 13-18 μm) and the epithecium is brown to dark brown in the second species.

A dichotomous key is presented with the species of Rhytidhysteron accepted by Index Fungorum (2021), including the three new species proposed in this work. The key includes the recently described R. mexicanum Cobos-Villagrán, Raymundo, Calvillo-Medina & R. Valenz and R. hongheense Wanas. It should be noted that R. fuscum (Ellis & Everh.) J.L. Bezerra & Kimbr. and R. minor (Cooke) A. Pande are not considered because the first belongs to the genus Tryblidiella and the second is a nom. inval., because the basionym was not indicated and bibliographic reference omitted (Art. 41.5, see Art. 41.7, Melbourne).

Figures

Figure 4. Rhytidhysteron mesophilum (Holotype, A. Trejo 74) A appearance of ascomata hysterothecial on host B ascomata hysterothecial close-up, striated margin with yellowish green pruina and reddish orange to orange red epithecium C-F microscopical features stained with alcohol (70 %) and KOH (10 %) reagent C ascomata hysterothecial cross-section with alcohol (70 %) D exciple of iso-radiating cells (textura prismatica), close up E asci F ascospores.