The RBBM includes several biogeographical regions (“Sierra Madre Oriental” and “Eje Neovolcanico Transmexicano”) and presents at least six, mainly dry vegetation types: xerophytic scrub, submontane scrubland, deciduous tropical forest, coniferous forest, grassland and riparian vegetation (Rzedowski 1978, Morrone 2001, CONANP 2003). In order to elaborate the map (Figure 1), we also considered the information about the use of soil and nine types of vegetation (e.g. agricultural, Quercus forest, among others) provided by INEGI (2017).

The RBBM has an area of 960.42 km² and is located in the eastern-central region of Hidalgo State (19°35'52"–21°25'00"N and 97°57'27"– 99°51'51"W) (Figure 1). The topography is rugged and the altitudinal gradient ranges from 1100 to 2600 m a.s.l., which determines the presence of different climates and vegetation types. The climate varies from semi-dry to temperate dry, with an annual average temperature of 18–22 °C and average annual rainfall of 400–700 mm (CONANP 2003). This area constitutes a biological corridor between the Nearctic and Neotropical regions; it is located in northern Mexico and includes eight municipalities.

Figure 1. 

Map of the study area indicating: A Location of the RBBM in Hidalgo State and municipalities, and B Vegetation types.

Fieldwork in bromeliads has been conducted in RBBM since 2008. All collected specimens are housed in the Centro de Investigaciones Biológicas Herbarium (HGOM) of the Universidad Autónoma del Estado de Hidalgo. On the other hand, orchid data from the herbarium HGOM or from fieldwork, started to be collected and data-based in 2010.

For species identifications we used specialized botanical literature: Espejo-Serna et al. (2005, 2010), Pintado (2010), Ceja-Romero et al. (2010) and Hornung-Leoni (2017) for bromeliads and we reviewed Hágsater et al. (2005) and Soto-Arenas et al. (2007) for orchids. Dr. Gerardo Salazar identified the orchid specimens in HGOM. Bromeliads were identified by C. Hornung-Leoni and I. Ramirez-Morillo.

All our reports are strictly based on herbarium specimens deposited in several herbaria (AMES, AMO, CHAP, CICY, ENCB, GH, F, IEB, IBUG, MICH, MEXU, MO, UAMIZ, US, SEL, WU). Additionally, we used high resolution images from the same herbaria as well as online databases to complement some data (e.g. distribution and altitudes) (Table 1).

For authors, we followed Brummitt and Powell (www.ipni.org); for synonymy, we used The Plant List (www.theplantlist.org) and for the species names, we consulted Tropicos (http://tropicos.org/).

Information about endemism was obtained from previous studies about recently discovered new species (Espejo-Serna et al. 2004, Espejo-Serna 2012, Ramírez et al. 2015, Villaseñor 2016); as for risk categories, we consulted IUCN (2017), NOM-059-SEMARNAT (SEMARNAT 2010) and CITES (2017) (www.cites.org). For species with restricted distribution inside the RBBM limits (like Tillandsia tortilis, T. mauryana and Sotoa confusa), GeoCAT tool interface program (Bachman et al. 2011) was employed in order to calculate risk category sensu IUCN criteria, considering extent of occurrence (EOO) and area of occupancy (AOO) based on coordinates, for those cases in which we found at least three different collecting points as required by the software.

It is important to emphasize that several of the species found by us at RBBM were mentioned before in the literature (CONANP 2003, Vincenzo et al. 2012), but their presence based on previous reports is impossible to be confirmed since many of them lack herbarium specimens. Therefore, ours constitutes the first confirmed and verifiable report, since it is supported by specimens housed in public collections.

In the management plan of the RBBM (CONANP 2003), 12 bromeliads and orchids are cited; however, some nomenclatural problems need to be mentioned. First, among bromeliads they reported Tradescantia sp., a member of Commelinaceae, which needs to be discarded. Secondly, some of the cited species’ names are currently treated as synonymous or are invalidly published (sensu Plant List and Tropicos): for example, Tillandsia ehrenbergiana Hemsl., is a synonym of T. utriculata but we have no records of this last species in the study area. Tillandsia ehrenbergiana Klotzsch ex Baker is synonymous with T. tortilis and for this taxon we have several records. Another case is that of Tillandsia benthamiana Klotzsch ex Baker, currently treated as a synonym of T. erubescens, a taxon here reported for the RBBM. Tillandsia benthamiana var. andrieuxii Mez is recognized as T. andrieuxii, a species for which we also did not find specimens deposited in herbaria because we did not collect it in the study area. For these reasons, we consider that the correct names for the species previously cited for the area (CONANP 2003) are T. tortilis and T. erubescens. Moreover, even if they are synonyms, these species have not been found in herbaria until now. So, T. tortilis and T. erubescens were considered as new records because our vouchers are the first ones collected for both species.

For orchids, in the management plan (CONANP 2003) species like Cyrtopodium macrobulbon, C. punctatum and Epidendrum ramosissimum Ames & C. Schweinf. were reported, even though the last species is only documented for Costa Rica; it is probably a case of misidentification and will not be clarified since there is no specimen or image to verify this report. Other orchid species reported for the RBMM (sensu Vincenzo et al. 2012), are Anathallis minutalis, Epidendrum ramosum, Laelia autumnalis, L. gouldiana, L. anceps, and L. speciosa. The management plan reports the presence of E. ramosissimum that Vincenzo et al. (2012) recognize as E. ramosum, but both are only literature references. For this reason they are not included in the present study. For Pleurothallis minutalis (sensu CONANP 2003 and Vincenzo et al. 2012), currently treated as Anathallis minutalis, its presence has not been collected yet for the orchid flora of Hidalgo State (Chavarria et al. in prep.).

Since RBBM provides many habitats, vegetation types and different substrates, the Reserve is a relevant area for the preservation of the flora in the state and as more collections become available the numbers reported here for endemism may change, since they are affected by the collection effort as well as the growing knowledge about species distribution. The number of species present in the RBBM is considerable, in relation to the area occupied by this reserve within the State. Nevertheless, this fact was not unexpected because it is the largest Reserve of Hidalgo State and includes several vegetation types as well as a variety of climatic and environmental conditions. In spite of this richness, in our opinion the diversity of bromeliads and mainly orchids has been underestimated. This is unsurprising considering that Rzedowski (2015) mentioned that knowledge of Mexican flora is still a work in progress with approximately 30% of species still unknown.

The greatest richness in the RBBM is represented by Laelia for orchids and Tillandsia for bromeliads, the latter being the most diverse genus of the bromeliads in Hidalgo (Hornung-Leoni 2017). Some of them are still poorly collected. For example, Tillandsia tortilis, has been reported before outside the limits of Metztitlán (Ceja-Romero et al. 2010), but we found this species inside the RBBM near its borders. We consulted some local people who commented that they do not have any interest in this plant since they only consider it as a parasite and, in some cases, it is removed from trees. Another species, T. recurvata, is very abundant in Prosopis spp. trees and other bushes in the Reserve. Sterile individuals of Hechtia deceptrix, a recently described species endemic to Hidalgo (Ramírez et al. 2015), were observed inside the RBBM (on the road from Metztitlán to Tolantongo). This finding extends the distribution of the species reported earlier by Ramírez et al. (2015) for the Carso Huasteco within the Sierra Madre Oriental Province (sensu Morrone 2014). However, the presence of this species inside the RBBM was expected since it is located in the same biogeographic area. Other species that we expected to find are Pitcairnia ringens (Bromeliaceae) and Dicromanthus cinnabarinus (Orchidaceae), since both of them have been reported near the limits of the RBBM, despite not being vouchered up to now.

The RBBM can be cited as an example of how a Reserve created for other purposes (e.g. to preserve Cactaceae), can be a refuge for other endemic, rare, and even new species like bromeliads and orchids. After completing floristic inventories, conservational strategies should be developed, counting on people who live inside the Reserve to assist in the species/habitats conservation. In fact, people living inside the reserve are very conscious of the natural resources they have, and may take part to protect the biota. Additional strategies may include ex-situ cultivation of threatened species and the promotion of campaigns to avoid extraction of individuals from their habitat.

Even though epiphytic species are dominant in RBBM, some species like T. juncea can be facultative (epiphytes and occasionally saxicolous). However, as was expected, the predominance of epiphytes is related to the presence of abundant tree species of the deciduous tropical forest. This means that species from different substrate preferences can coexist in the same habitat and vegetation type. For example, on scrubs (“matorral”) we can find epiphytes like T. juncea, and T. ionantha on cactus or even on rocks; on the other hand, saxicolous species as T. inopinata can also grow as epiphytes in the same area.

Most orchids seem to be facultative; for example, species of Laelia generally appear as epiphytes, although it has been reported that L. speciosa and L. anceps can be saxicolous in other regions (Halbinger and Soto-Arenas 1997, Soto-Arenas and Solano-Gómez 2007). Another orchid that can also be facultative is Mesadenus polyanthum; the remaining species here reported are limited to one type of habit (epiphyte, saxicolous, or terrestrial).

Due to the variation in orography, vegetation types and climates found within the RBBM, it is possible that different species can find there an appropriate microclimate/niche to grow. For example, from the species cited in Table 1, orchids like Laelia and Cyrtopodium species, as well as bromeliads of the genus Hechtia, and particularly Tillandsia albida and T. inopinata, are found in xerophytic areas; while in humid environments one may find orchids like Aulosepalum and Sarcoglottis and bromeliads as T. violacea, T. imperialis, and T. deppeana.

Some species of bromeliads and orchids grow in drier habitats (Gentry and Dodson 1987) which is related to CAM metabolism and economy of water (Benzing 1990, Fontoura and Reiniert 2009). For example, T. mauryana and T. ionantha grow in xerophytic areas and are adapted to water stress conditions (Benzing 2000). Both have CAM metabolism that may be used for saving water (Benzing 2000, Matiz et al. 2013).

Orchid diversity is considered low in arid areas because there are limiting factors, like water and type of soil that are essential for mycorrhizae formation and seed germination. Even in rocky sites, organic soil matter is usually low or almost nonexistent and hence a limitation (Hágsater et al. 2005). Nevertheless, most of the species reported here are terrestrial and saxicolous. The epiphytic orchids depend not only on the mycorrhizae, but also on the characteristics of trees’ bark and the microclimatic gradients generated by their height (Benzing 1990, Shaw 2004), which could explain the low diversity presented by this habit.

A total of nine endangered or protected species are included in Table 1 (IUCN, CITES, NOM-059-SEMARNAT). The NOM-059-SEMARNAT only proposed Tillandsia festucoides and Laelia speciosa as species subject to special protection; T. imperialis is referred to as a threatened species, and is locally used in beverages (as food or as medicine) by people in Hidalgo (Hornung-Leoni 2011 a,b). Laelia anceps is also mentioned as an endangered species and L. gouldiana as an extinct one (in situ). On the other hand, the IUCN list only considers T. ionantha as a Least Concern (LC) category, and CITES (2017) includes species like T. mauryana, L. anceps, L. gouldiana and L. speciosa as Endangered and states that for Laelia, the main problem is its use as an ornamental plant subjected to extraction of individuals from the wild for the horticultural trade.

Tillandsia mauryana is considered at risk in CITES appendices (2017). According to Espejo-Serna et al. (2004), this species is saxicolous and endemic to Mexico, for the states of Hidalgo, Jalisco, Oaxaca, and Zacatecas. More recently, Espejo-Serna and López-Ferrari (2018) considered T. mauryana endemic to Hidalgo, a fact that we have corroborated after reviewing specimens collected in the field and in herbaria. We detected some areas in the RBBM where the species covers a rocky wall, while in other areas only a few individuals are present. In general, we observed scanty populations of T. mauryana in the Reserve (see IUCN category assigned in Table 1). No particular use of this species in local trade was reported here, but due to the small number of these populations and to their potential use as ornamental plants, some kind of protection is needed (see Table 1 for IUCN status). Furthermore, it needs to be protected due to the slow population growth rate and the frequent extraction of rocks in the Reserve area (Valverde-Valdés 2013). For those species that are not yet used by local people, the principal risk is habitat destruction.

In Orchidaceae, Laelia has categories subject to protection in both CITES and NOM-059-SEMARNAT, since species are exploited commercially and for cultural uses during local festivities. Nevertheless, they are not included in any of the IUCN categories.

Laelia gouldiana is the most exploited species and although it is reported as extinct in situ (NOM-059-SEMARNAT), it is common to find it in local houses’ backyards inside RBBM, a preponderance that has probably contributed to perpetuate its existence. For the remaining orchid species reported in the RBBM, there are no known ethnobotanical uses. Terrestrial orchids are recognized as such by very few people and are susceptible to vegetation fires during the dry season and to changes in the use of soil.

For bromeliads, principally tillandsias were included in the management plan (CONANP 2003), but some of them are synonymous or misidentifications. Three out of six species of the orchids included in the management plan are Laelias [L. autumnalis, L. gouldiana and L. speciosa (Kunt) Schltr]. The last two can be found in NOM-059-SEMARNAT, in the categories of extinct in nature and in special protection, respectively (SEMARNAT 2010).

Both families are important because they not only provide biological resources to pollinators, visitors and fauna, which fulfill at least a part of their life cycles in these plants (Benzing 2000, Hornung-Leoni et al. 2013), but because they are also used by local people for ornamental, medicinal and ceremonial purposes (Hornung-Leoni 2011a).

Orchids such as Laelias are considered beautiful, abundant and easy to grow and are commonly used in religious celebrations such as the Día de Muertos (Day of the Dead) (Hágsater et al. 2005). Due to the flowering period of L. anceps and L. gouldiana, it is common to find them in November as an ornamental element in altars, tombs, and churches. For people who live inside the RBBM, L. gouldiana is a well-known and widely cultivated species to be used during November festivities and represents an occasional economic income as well (Soto-Arenas and Solano-Gómez 2007). As for L. speciosa, we found only one publication in which food and ornamental uses in Hidalgo are included (Pérez Escandón et al. 2003), even though we could personally verify that it is locally sold at Actopan markets in May. Although García-Peña and Peña (1981) report the use of pseudobulbs of Cyrtopodium macrobulbon to prepare cataplasms, it is not known if local people of the RBBM apply the same use to this or other species.

Bromeliads and orchids are important in areas that have a conservation focus. It is clear that areas with species under threat like RBBM are important for Mexico if there is, as we think, the intention to create corridors for plants and pollinators.

Summarizing, bromeliads are important components in RBBM, with predominance of Tillandsia species, and with a high component of Mexican endemism inside the Reserve. The number of species of orchids has been underestimated and needs to be explored further in the future. Even if the principal habit is epiphytic, both families represent important elements for species diversity in the RBBM, as well as a dominant component in some habitat types. The endemism inside the RBBM highlights the necessity of preserving this variable area and enhancing environmental education and ethnobotanical studies together with local people.