Introduction
Oaxaca is one of the Mexican states with highest plant species richness (Garcia-Mendoza & Meave 2011, Villasenor 2016), hosting about 10,000 taxa of vascular plants. The Bromeliaceae family is represented in Oaxaca by 184 species, which corresponds to 44% of the Mexican bromeliad flora (Espejo-Serna et al. 2007, Espejo-Serna & Lopez-Ferrari 2018). About 29% (53 spp.) and 67% (124 spp.) of these species are endemic to the state and to the country, respectively.
The Regiones Terrestres Prioritarias (Terrestrial Priority Regions) Project (RTP's) was proposed in the year 2000 by the Comision Nacional para el Conocimiento y Uso de la Biodiversidad (CONABIO) to determine the most biodiverse areas of Mexico, considering their species and ecosystem richness, with the purpose of establishing policies for the future conservation of biodiversity. The RTP's were spatially defined according to natural features of the landscape, including topography, watersheds, soil and vegetation types, together with the range of distribution of certain key species. The presence of protected natural areas, as well as first-hand knowledge provided by experts were also considered when defining the final boundaries of the RTP's (Arriaga et al. 2000). In the state of Oaxaca eight RTP's were considered: Cerros Negro-Yucano, Sierras Triqui-Mixteca, El Tlacuache, Bajo rio Verde-Chacahua, Sierras sur y costa de Oaxaca, Sierras del norte de Oaxaca, Mixe, and Selva Zoque-La Sepultura. The RTP Cerros Negro-Yucano is located in the NW portion of the state [16[degrees]57'49"-17[degrees]40'36" N, 97[degrees]15'21"-97[degrees]33'48" W], and comprises a surface area of 1,274 [km.sup.2] (Arriaga et al., 2000), that represents 1.35 % of the state's territory that covers partially or totally 31 municipalities of the 570 registered for Oaxaca (Fig. 1). The vegetation types present in this region are oak forest, pine forest, juniper forest, tropical deciduous and semi-evergreen seasonal forests, as well as desert scrub and palm grove. The elevation ranges from 1,300 to 3,200 m a.s.l.
As part of a Master's thesis about The Epiphytic Angiosperms of the RTP Cerros Negro-Yucano (Gomez-Escamilla, 2016) botanical sampling (Fig. 2) was carried out between January 2014 and February 2015 in different locations of the region, especially in areas covered by oak forests (Fig. 1). Plant material of all epiphytic angiosperms was collected, photographed in situ, and herbarium specimens were deposited at the herbarium UAMIZ (Herbario Metropolitano, Universidad Autonoma Metropolitana Iztapalapa), located in Mexico City. Here we present the data obtained for the Bromeliaceae.
Results
A total of 20 epiphytic bromeliad species of the genera Tillandsia and Viridantha were present in the RTP Cerros Negro-Yucano (Table 1, Figs. 3-12). Most species occur in oak forests, with the exception of Tillandsia circinnatioides, T. fasciculata and T. tehuacana,...