Phytotaxa 528 (1): 019–044 https://www.mapress.com/j/pt/ Copyright © 2021 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Eric McKenzie: 23 Nov. 2021; published: 9 Dec. 2021 https://doi.org/10.11646/phytotaxa.528.1.3 19 Ascomycetes from the relic forest of Oreomunnea mexicana, Oaxaca, Mexico RICARDO VALENZUELA 1,4 , TANIA RAYMUNDO 1,5 , PAMELA REYES 1,6 , JORGE GUZMÁN-GUILLERMO 2,7 , SALVADOR ACOSTA 1,8 , JULIO CESAR RAMÍREZ-MARTÍNEZ 3,9 & ISOLDA LUNA-VEGA 3,10 * 1 Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica, Laboratorio de Micología, 11340 Mexico City, Mexico. 2 Facultad de Biología, Xalapa, Universidad Veracruzana, circuito Gonzalo Aguirre Beltrán s/n, zona universitaria, 91090, Xalapa- Enríquez, Veracruz, Mexico. 3 Laboratorio de Biogeografía y Sistemática, Departamento de Biología Evolutiva, Facultad de Ciencias, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico. 4 � rvalenzg@ipn.mx; https://orcid.org/0000-0001-6596-5223 5 � traymundoo@ipn.mx; https://orcid.org/0000-0002-7525-0034 6 � pamreyesrdgz@gmail.com; https://orcid.org/0000-0003-0882-5245 7 � qwerty.guzmi@gmail.com; https://orcid.org/0000-0003-2137-3028 8 � salvacst@gmail.com; https:// orcid.org/0000-0002-4388-4032 9 � rasec.jc@ciencias.unam.mx; https://orcid.org/0000-0001-5393-4251 10 � luna.isolda@gmail.com; https://orcid.org/0000-0002-7243-9018 *Corresponding author: � luna.isolda@gmail.com Abstract La Esperanza is an Oaxacan relic area of the Tertiary, dominated by the big tree Oreomunnea mexicana (Juglandaceae). The forest is part of the priority region for the conservation of La Chinantla and constitutes one of the most conserved Mexican tropical montane cloud forests. We studied the Ascomycetes fungi and found 63 species, of which 32 are new records for Oaxaca. Ascocoryne inflata, Calyculosphaeria macrospora, Cercophora costaricensis, Chaetosphaeria ellisii, Coccomyces limitatus, Lasiosphaeria ovina, Leptogidium dendriscum, Marthamyces quadrifidus, Stereocaulon didymicum and Thelonectria lucida are new records for Mexico. Xylaria was the most diverse genus with 12 species. The most abundant species were Xylaria arbuscula and Lachnum apalum. The main growth habit was lignicolous. The tropical montane cloud forest of La Esperanza has unique characteristics allowing great taxonomic diversity of Ascomycetes. Keywords: conservation, endemism, fungi, mountains, tropical montane cloud forests Introduction Phylum Ascomycota is the largest group within the Fungi kingdom. Kirk et al. (2008) mentioned that there are 64,163 species worldwide, while for Mexico, González & Hanlin (2008) presented a compilation of 1331 species, of which 35% are lichenized fungi. One of the most diverse habitats is the tropical montane cloud forest (TMCF) for its great diversity of plants, animals, and fungi concentrated in a small area (Toledo-Aceves et al. 2011, Calderón-Aguilera et al. 2012). The distribution pattern of the TMCF in Mexico is discontinuous, analogous to an “island archipelago” of humid forests surrounded by other vegetation types (Luna-Vega et al. 1999, CONABIO 2010). The tropical montane cloud forest in northern Oaxaca has Oreomunnea mexicana (Standl.) J.-F. Leroy as the absolute dominant element in the upper tree layer, with a 30–40 m height. This tree is considered a relic element of the Cenozoic. This association type is represented between 1400–2250 m, and it contains diverse plant associations formed by Ilex sp., Clethra conzattiana L.M. González, Oreopanax sp., Clusia lundellii Standl., Symplocos jurgensenii Hemsl., Persea rufescens Lundell, P. albida Kosterm., P. chiapensis Lundell, Ternstroemia tepezapote Schltdl. & Cham., Zanthoxylon melanostictum Schltdl. & Cham., Ocotea effusa (Meisn.) Mez, O. sarcodes Lorea-Hern., O. betazensis (Mez) H. van der Werf, Hedyosmum mexicanum C. Cordem., Podocarpus matudae Lundell, Alchornea latifolia Sw., and different genera of Lauraceae and Ericaceae. The tree fern Cyathea fulva (M. Martens & Galeotti) Fée is conspicuous. The Oreomunnea trees are densely covered by vascular and non-vascular epiphytes, and Tillandsia