Introduction

Among the Hymenochaetaceae, the genus Hymenochaete Lév. is the best represented in terms of its number of species. It has been described by Léveille in 1846, with the type species Hymenochaete rubiginosa (Dicks. Fr.) Lév., and belongs to the order Hymenochaetales, class Agarycomycetes of the phylum Basidiomycota. It is characterized by a smooth basidiome, ranging from stipitate to resupinate, with a monomytic hyphal system, numerous setae in the hymenium, and a xanthochroid reaction (^{Parmasto, 2001}). The fungi of the genus Hymenochaete are xylophagous, since they feed on the wood of logs and/or fallen branches and obtain their energy from the decomposition of substrates such as cellulose, hemicellulose and/or lignin, a process known as wood rot. Its representatives are mainly distributed in tropical areas, but have also been found in temperate zones parasitizing young willow plants, and on cocoa, cotton, rubber tree, breadfruit, and camphor tree in tropical regions; causing death in its hosts (^{Parmasto, 2001}). Approximately 130 species have been described in the world (^{Léger, 1998}), and 28 for North America (^{Parmasto, 2001}). In Mexico, 24 species have been cited (Table 1). The present study is aimed at describing Hymenochaete liliae as a new species. Its morphological description, distribution as well as habitat are presented. Moreover, a taxonomic key of the species that exist in Mexico is included.

Materials and Methods

Specimens of the new species were collected on the Cerro Negro, Santiago Laollaga municipality, in the southeast of the state of Oaxaca, Mexico (Fig. 1), specifically in the region of the Isthmus of Tehuantepec. The municipality is located at an average altitude ranging around 110 m a.s.l. In this area, the vegetation is characterized by tropical dry forest (^{Rzedowski, 1978}). In this type of ecosystem there is an arboreal stratum with extended crowns, with an average height of 7 to 8 m, for example Conzattia multiflora (Robinson) Standl., Pithecellobium dulce (Roxb.) Benth., Enterolobium cyclocarpum (Jacq.) Griseb., Ficus petiolaris Kunth and species of Bursera Jacq. ex L. The shrub stratum has an altitude that varies from 3 to 6 m; characteristic taxa are Acacia Mill., Cordia (P. Browne) G. Don., Croton L., Malpighia L., Manihot L., Liabum glabrum Hemsl., Salvia sessei Benth. and Dioon edule Lindl. Columnar and candelabriform cacti can also be found, such as Pachycereus (A. Berger) Britton & Rose, Stenocereus (J.G. Ortega) Buxb., Cephalocereus Pfeiff., and Opuntia Mill. (^{Trejo, 1999}). The herbaceous stratum depends on the shadow cast by the canopy; examples are Bromelia L., Begonia heracleifolia Schltdl. & Cham., Callisia fragrans (Lindl.) Woodson and Dorstenia contrajerva L.

Figure 1: Type locality of Hymenochaete liliae Contr.-Pach., R. Valenz., Raymundo & Pacheco in the Istmo region, Tehuantepec district (southeast of the state), municipality Santiago Laollaga, Oaxaca, Mexico. 

The following specialized literature on the genus Hymenochaete was reviewed: ^{Reeves and Welden (1967)}, ^{Léger (1998)}, ^{Parmasto (1985}; ²⁰⁰¹⁾, ^{Dai (2010)}, ^{Wagner and Fisher (2002)} , ^{He (2010)}; ^{He and Li (2011a}, ^b, ^c; ²⁰¹²⁾, ^{He and Dai (2012)}, ^{Parmasto et al. (2014)}, ^{Nie et al. (2017)} and ^{Contreras-Pacheco et al. (2018)}. Additionally, specimens from the herbaria FCME of the Facultad de Ciencias, Universidad Nacional Autónoma de México, and ENCB, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, were studied.

A morphological study was carried out following the protocol of ^{Léger (1998)} and ^{Parmasto (2001)}, which was based on the fresh material collected by the authors. Organoleptic characters were recorded as well as basidiome colors coded from the Munsell soil color chart (^{Munsell Color, 2010}). Photographs were taken with a Nikon D7000 camera (Nikon, Tochigi and Miyagi, Japan).

The different layers of the basidiome, length, width, shape and color of setae, hyphae, and basidiospores were observed using a Carl Zeiss model K-7 microscope (Mexico City, Mexico). Very thin cross sections of the basidiome were sectioned by hand using a commercial double-edged razor. The sections were mounted in preparations with 70% alcohol and 5% KOH for rehydration, and examined under the microscope with 10, 40 and 100 × objectives. Photographs of the microscopic features were taken with a Nikon Colpix 4300 camera (Nikon, Tochigi and Miyagi, Japan).

Finally, we here present a dichotomous key of the Mexican Hymenochaete species modified from ^{Parmasto (2001)}, based on macroscopic and microscopic characters (presence/absence of the different layers that constitute the basidiome, shape and size of the mushrooms, spores, etc.).

Results

Hymenochaete liliae Contr.-Pach., R. Valenz., Raymundo & Pacheco, sp. nov. Fig. 2.

Figure 2: Hymenochaete liliae Contr.-Pach., R. Valenz., Raymundo & Pacheco. A. setae; B. spore; C-D. basidiome. 

TYPE: MEXICO. Oaxaca, Istmo region, Tehuantepec district (southeast of the state), municipality Santiago Laollaga, Cerro Negro, 110 m, 16°41'41.3''N, 95°17'26.1''W, tropical dry forest, 25.X.2014, M. M. Contreras-Pacheco 001 (holotype: ENCB!). Mycobank: 840975.

Hymenochaete liliae differs from H. cinnamomea (Pers.) Bres. because the former has acute setae, with crystals, abundant throughout the hymenium; ellipsoid basidiospores, while the latter presents acute setae, without crystals, arranged in the different layers of the basidiome, and cylindrical basidiospores.

Basidiomata 23-46 × 9-12 mm, resupinate, adhered to the substrate, consistency membranous-fleshy, growing in circles that are fused; hymenophore smooth, color suede (10YR 6/6); margin determined, concolor with the hymenophore; without tomentum or cortex; hymenium 25-30 µm wide, subiculum 50-70 µm wide, with crystals; hyphal system monomitic, subhymenal hyphae 2.5-3 µm diameter, yellowish, continuous, septa simple; hyphae of the subiculum (together with the substrate) 5-6 µm diameter long, wall wide, 1 µm wide, brown, septa simple; setae 69-80 × 6-8 µm, thick-walled, covered with crystals, apex acute, 50 µm long, protruding from the hymenium, brown, abundant; basidia 24-26 × 3-5 µm, cylindrical, torulous, tetrasporic, sterigma 3-4 µm; basidiospores 5-8 × 2-3 µm, ellipsoid, thin-walled, smooth, hyaline.

Habitat: lignicolous, found growing on woody remains of a leguminous tree.

Etymology: the name of this species is dedicated to the biologist Lilia Pérez-Ramírez, a pioneer in the study of corticioid fungi in Mexico.

Additional material studied: MEXICO. Oaxaca, Istmo region, Tehuantepec district (southeast of the state), municipality Santiago Laollaga, Cerro Negro, 110 m, 16°41'41.3''N, 95°17'26.1''W, tropical dry forest, 26.X.2014, M. M. Contreras-Pacheco 002 (ENCB, paratype).

We here present an identification key for all known species of the genus Hymenochaete in Mexico.

Discussion

Hymenochaete liliae belongs to Hymenochaete section Fultochaete Esc. ex Léger, because it lacks cortex. It is characterized by its suede color, thin setae, 69-80 × 6-8 µm, basidiospores 5-8 × 2-3 µm. It can be differentiated from H. cinnamomea (Pers.) Bres. because it does not present a basidiome with setae in different layers, and has ellipsoid basidiospores. Although it resembles H. rhabarbarina (Berk.) Cooke, it differs from the latter species because of its setae covered with crystals, and its spores measuring 4.5-5 × 2.5-3.5 µm. The old specimens of H. rhabarbarina have setae arranged in 2-3 obscure layers, and incrustation setae have reddish brown granules (^{Parmasto, 2001}). Furthermore, it could be confused with H. minuscula G.H. Cunningham due to its mustard color; however, the setae (40-60 µm) and basidia (15-20 µm) are smaller, and H. minuscula has not been reported for Mexico (^{Dai, 2010}).