Lianas of Mexico

Lianas de México

Guillermo Ibarra–Manríquez^1,3, Francisco Javier Rendón–Sandoval¹, Guadalupe Cornejo–Tenorio¹ and Pablo Carrillo–Reyes²

¹ Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México. Morelia, Michoacán, México.

³ Corresponding author: gibarra@cieco.unam.mx

Received: May 2nd, 2014.
Accepted: September 15th, 2014.

Abstract

Through an exhaustive literature review, field exploration and revision of herbaria, the presence of 861 native species of lianas in Mexico is documented, pertaining to 250 genera and 59 families. A total of 25.9 % (n = 224) of the species and three genera are endemic to Mexico. The 15 most diverse families account for 80.1 % of the species and 85.7 % of endemics. The 18 richest genera comprise 38.1 % (n = 328) of the species and approximately 50 % of the endemic. Chiapas is the state with the greatest diversity because it includes 65.4 % of the total species, whereas Oaxaca is the richest state in terms of endemism (49.6 %). Regardless of their area, the most diverse states are also notable for their endemism. The lianas found in only one state encompassed 16.5 and 26 % of the total number of species and endemics, respectively. Among the five recognized biomes in Mexico, the tropical humid forest and the tropical seasonally dry forest stand out for their number of species (n = 692, 80.3 %) and number of endemics (n = 134, 59.8 %), respectively. At the level of vegetation type, the tropical deciduous forest ranks first in both attributes. The number of lianas species decreased significantly with altitude. Our results demonstrate the importance of the contribution of lianas to the richness and endemism of Mexican flora and justify the development of initiatives to ensure their long–term conservation.

Key words: altitudinal gradients, biomes, diversity, endemism, vegetation types.

Por medio de una exhaustiva revisión bibliográfica, trabajo de campo y la revisión de ejemplares de herbario, se documenta la presencia de 861 especies de lianas nativas, incluidas en 250 géneros y 59 familias. El 25.9 % (n = 224) de las especies y tres géneros son endémicos de México. Las 15 familias más diversas concentran el 80.1 % del total de especies y el 85.7 % de las endémicas. Los 18 géneros con mayor riqueza concentran 38.1 % (n = 328) de las especies de lianas y cerca del 50 % de las endémicas. A nivel de estados, Chiapas es el más sobresaliente, ya que registró el 65.4 % del total de especies, mientras que Oaxaca lo fue para las endémicas (49.6 %). Los estados muestran una alta congruencia entre la riqueza de especies y grado de endemismo, atributos que no se explican por el área que éstos presentan. Las lianas restringidas a un solo estado representaron el 16.5 y 26 % del número total de especies y endémicas, respectivamente. Entre los cinco biomas reconocidos para México, el bosque tropical húmedo destacó por su número de especies (n = 692, 80.3 %), mientras que el bosque tropical estacionalmente seco hace lo propio para las endémicas (n = 134, 59.8 %). Por tipo de vegetación, la primera posición para ambos atributos es para el bosque tropical caducifolio. El número de especies de lianas decreció significativamente con la altitud. Los resultados del presente estudio demuestran que la contribución de las lianas a la riqueza y endemismo de la flora de México es relevante, lo cual justifica iniciativas particulares que permitan asegurar su conservación a largo plazo.

Palabras clave: biomas, diversidad, endemismo, gradientes de altitud, tipos de vegetación.

The climbing habit has evolved on many occasions in plants and has been detected in at least 133 families of Angiosperms (Gentry, 1991a; Schnitzer and Bongers, 2002; Gallagher and Leishman, 2012). The independent evolution of this habit in so many lineages could be explained because climber species invest fewer resources in the development of their stems compared to erect plants, enabling this group to direct these resources toward other important functions, such as growth or water capture (Schnitzer et al., 2005; Wyka et al., 2013). Lianas play an important role in the taxonomic and functional diversity in tropical forests, especially during early succession stages, as well as interaction with a high number of pollinators and frugivores (Gentry 1982, 1991a, b; Solórzano et al., 2002; Schnitzer and Bongers, 2002; Letcher and Chazdon, 2012). For example, the complete floristic inventories of particular locations demonstrate that this growth form can account for between 8 and 24 % of the woody species (Gentry and Dodson, 1987; Ibarra–Manríquez and Sinaca, 1995; Meave et al., 2008). Inventories in plots of 0.1 ha have revealed that an average of 18 % of stems with DBH (diameter at breast height) ≥ 2.5 cm belong to lianas (Gentry, 1991a) and in similar censuses in Mexican tropical dry forests are absent or may represent up to 25 % of the species present, with an average of 10.4 ± S.D. 7.1 (Lott et al., 1987; Trejo and Dirzo, 2002; Pineda–García et al., 2007; Martínez–Cruz et al., 2013).

Due mainly to the magnitude of Mexican floristic diversity, which is estimated to be at least 22,000 species of Angiosperms (Rzedowski, 1991a; Espejo–Serna et al., 2004a; Villaseñor and Ortiz, 2014), the species richness of all of the present growth forms is not equally known. Undoubtedly, the trees and the epiphytes are those that are best characterized because these are the subjects of relatively recent floristic publications (e.g. Ibarra–Manríquez et al., 1995; Espejo–Serna et al., 2004b; Hágsater et al., 2005; Cué–Bär et al., 2006a; Padilla–Velarde et al., 2006; Soto–Arenas et al., 2007; González–Espinosa et al., 2011; Ricker et al., 2013). However, no such compendia exist for the lianas.

An important source of information to know the richness of lianas are the regional floristic projects [e.g. Flora del Bajío y de Regiones Adyacentes (Rzedowski and Calderón, 1993; Calderón et al., 2004), Flora de Veracruz (Pérez–Cueto, 1995; Ortega and Ortega, 1997) or Flora del Valle de Tehuacán–Cuicatlán (Juárez–Jaimes and Lozada, 2003; Alvarado–Cárdenas, 2004)], local floristic inventories (e.g. Ibarra–Manríquez and Sinaca, 1995, 1996a, b; Lott, 2002; Meave et al., 2008) and checklist available to Mexico for some families with many lianas representatives (Borhidi, 2006; Juárez–Jaimes et al., 2007; Anderson, 2013).

Specimens that are deposited within herbaria also are another key tool to know diversity of Mexican lianas, although a critical taxonomic review of the material is required. Nonetheless, this task is generally difficult to implement for several reasons: (i) lianas are underrepresented in herbaria because of collection difficulty, (ii) specimens often lack structures that are critical for accurate identification, (iii) collections, in many cases, are not revised by specialists, and (iv) there is a scarcity or absence of monographs of several climber families or genera.

On the other hand, estimates of the taxonomic richness of Mexican lianas differ because Rzedowski (1991a) suggested that there are 60 genera and 300 species, while Ibarra–Manríquez et al. (2015) indicated 214 and 754 taxa in these two taxonomic categories, respectively. The difference between these figures is due, among other factors, to the concept of the liana that is held by each of these authors, as well as the sparse floristic knowledge that exists regarding this growth form, which difficult its inventory. To accurately estimate the contribution of lianas to floristic diversity in Mexico, our fundamental objective is to list the species of lianas in this country, indicating the states, vegetation types, and altitudinal intervals in which they are found, as well as the species that restrict their geographic distribution to Mexico (endemic species).

Mexico has a land area of close to two million km². The country has been subject to complex geological changes throughout its history (Ferrusquía–Villafranca, 1993) that have caused the topography, with the exception of the Yucatán peninsula, to be dominated by mountains. Rzedowski (1978) states that only 35 % of the country is below 500 m asl, while more than half is above 1,000 m altitude, with the highest peaks found along the length of the Trans–Mexican Volcanic Belt, where the volcano Pico de Orizaba (Citlaltépetl) stands at 5,636 m elevation. Such a heterogeneous landscape, along with the position of the country astride the Tropic of Cancer, have produced a broad range of climates and vegetation types, including practically all of those that are recognized worldwide (Rzedowski 1978, 1991a). According to the Köppen classification, the climates that affect the greatest territorial area are (Kottek et al., 2006): A (tropical wet, with the mean temperature in the coldest month greater than 18 °C), B (dry, with a mean temperature in the coldest month greater or less than 18 °C and a mean annual temperature between 18 and 22 °C), C (temperate wet, with a mean temperature in the coldest month between –3 and 18 °C and in the hottest month greater than 10 °C) and, in very reduced areas and high altitude locations of the volcanoes of central Mexico, E (cold, with a mean temperature in the hottest month less than 10 °C). Rzedowski (1978) recognized four biogeographic regions (Pacific North American, Montane Mesoamerican, Xerophytic Mexican and Caribbean) that include 17 provinces. The number of recognized vegetation types range from ten (Rzedowski, 1978) to 32 (Miranda and Hernández–X., 1963). These publications describe the physiognomic characteristics and principal floristic components of these plant communities, as well as the climates and soil types in which they are found. In global terms, floristic affinities are more meridional than boreal, and, according to the fossil evidence, their origin goes back to at least the Cenozoic era, some 65 million years ago (Rzedowski, 1991a, b).

Materials and methods

There is no accurate definition by which to categorize liana species; however, they are generally described as climbing plants with woody stems that cannot remain upright autonomously once they have germinated in the soil (Gentry, 1991a; Bongers et al., 2002). Unfortunately, these basic attributes are not known for many species. For example, the designation of a plant as woody is not simple because this characteristic may be presented in individuals with very thin stems (i.e. ≤ 1 mm diameter) or only toward the base of stems. This information is rarely included in floristic publications that report climber species or in their descriptions of herbarium specimens and is even often neglected in taxonomic descriptions. The need of information is even more acute for germination in the soil, which is the main characteristic by which to separate lianas from woody climbing hemiepiphytes because the latter only germinate on the trunks or branches of trees (Gentry, 1991a). Another aspect that is difficult to evaluate is whether the plants are erect or require support for growth because this can vary with the age of the plants or in different vegetation types. An example of this situation is Salacia cordata (Miers) Mennega (Celastraceae), which is a liana that we can found in the upper canopy in the tropical evergreen forest but when young, is as small erect tree that grows up to a height of 3 m in the Los Tuxtlas Tropical Biological Station in Veracruz. At this same site grows the liana Celtis iguanaea (Jacq.) Sarg. (Cannabaceae), which in the tropical deciduous forest of the Chamela–Cuixmala region in Jalisco, can exhibit the liana habit or may grow as a shrub.

To assign a native species as liana (naturalized species were excluded), we considered: (1) the floristic–taxonomic literature (Appendix 1) and specimens that were deposited in herbaria (IEB, MEXU, MO, and XAL) where the species is described as a liana or woody climber, even if this condition is only presented towards the stem base, and (2) field observations in different parts of the country examining climbing species to evaluate the degree of woodiness (Figure 1) and to collect specimens with flowers and/or fruits in order to identify correctly the species (Figure 2 and 3). Consequently, the list also includes: (i) species that exhibit a growth habit that is similar to that of the lianas but do not germinate in the soil (hemiepiphytes), (ii) those that have a highly lignified atactostele (monocots, members of the families Arecaceae and Smilacaceae) or (iii) scandent shrubs with climbing branches that are greater than 5 m in length. Therefore, one or more of the following three growth forms were assigned to the species (Appendix 2): liana (including monocots), hemiepiphytes, and scandent shrubs. The identification of the specimens in the herbaria was verified by specialists or by the authors using monographs.

The altitude, vegetation type, and geographical distribution were obtained from the examined literature and herbarium specimens. Endemic species were those lianas only found in Mexico, whereas microendemics were identified such those species that are recorded in only one state of the country. Vegetation types and biomes were assigned according to the classifications of Rzedowski (1978) and Villaseñor and Ortiz (2014), respectively. In states with greater taxonomic richness, an analysis was conducted to determine whether the size of their territory could be a factor that explains this attribute. For this analysis, a weighted ratio was obtained between the number of families, genera, and species (total, endemics and microendemics) and the log10 of the area of each state. This value approaches the average richness of a given taxon in an area of 10 km2 (Rejmánek, 1996). The authors of the species and the publication in which they were described were recorded from the consulted literature (Appendix 1) and/or the database Tropicos (Tropicos, 2014).

Results

Taxonomic richness. Mexican native lianas are included in 59 families, 250 genera, and 861 species (Appendix 2). Among the three growth form categories that were recognized in this study, the lianas were the most important (n = 789 species), followed by the scandent shrubs (n = 246) and the hemiepiphytes (n = 26). A total of 15 families contributed differentially to the taxonomic richness of lianas because account for 70.4 % of the genera, 80.1 % of the total number of species, 85.7 % of the endemics and 84.2 % of the microendemics (Table 1). Apocynaceae dominated these four groups, followed by Fabaceae, except for the microendemic species, where second place was taken by Asteraceae. In contrast, 15 families were each represented by one species (Appendix 2).

The 18 genera with the greatest richness account for 38.1 % of the species (Table 2), with slightly higher percentages of endemic and microendemic taxa (45.1 % and 50.9 %, respectively). The reduced dominance of the most speciose genera compared to that documented for the families occurs because approximately half of genera present only one species (n = 114). The genus with the greatest number of species (n = 43) is Ipomoea (Convolvulaceae), whereas Serjania (Sapindaceae) and Passiflora (Passifloraceae) have 33 and 27 species (Table 2); the first place in the endemic species is Marsdenia (Apocynaceae), followed by Ipomoea and Matelea (Apocynaceae). Finally, standing out in terms of microendemic species are Serjania and Aristolochia (Aristolochiaceae), with six and five species, respectively.

Geographic distribution. A total of 25.9 % (n = 224) of the recorded species of lianas are endemic to Mexico, while only three genera (1.2 %) are included in this category (Balsas J.Jiménez–Ram. & K.Vega, Sapindaceae; Peponopsis Naudin, Cucurbitaceae; and Thoreauea J.K. Williams, Apocynaceae). Of whole sample of Mexican lianas, 57 species were recorded as microendemic (Table 3, Appendix 2), including those that were assigned to two endemic genera (Balsas guerrerensis Cruz–Durán & K.Vega restricted to Guerrero, Thoreaua aberrans J.F. Morales to Veracruz, T. guerrerensis Diego & Lozada–Pérez to Guerrero and T. paneroi J.K. Williams to Oaxaca).

Chiapas is highlighted at the state level (Table 3) because almost all of the families are recorded within its area (n = 57, 97 %), as well as 85.2 % (n = 213) of the genera, and 65.2 % (n = 562) of species. In these categories, Oaxaca presents very similar figures and therefore normally follows Chiapas in hierarchical order. In general, Veracruz occupies third place for these attributes of taxonomic richness, with the exception of the microendemic species, where second place is shared with Chiapas. Oaxaca encompass the greatest number of endemic species, with close to half of the total found in Mexico (n = 111), followed by Jalisco, Guerrero, and Michoacán, the percentages of which range from 34.8 to 39.7 %. Unexpectedly, the differences in area among the seven states that were cited in this section did not affect the position they occupy in these comparisons of diversity because the ratio values between the richness of taxa and the log10 of the area of each state follow the same pattern as described above using the number of species (Table 3).

The frequency with which the lianas have been recorded in the 32 states of Mexico indicate that 142 (16.5 %) and 109 (12.6 %) species are found in only one and two states, respectively (Table 4). Of the total species, 60.3 % have been found in up to five states, and only 18 (2 %) exist in more than 20 states. The most widely distributed species are Cardiospermum halicacabum L. (Sapindaceae, n = 31 states), Toxicodendron radicans (L.) Kuntze (Anacardiaceae, n = 27), and Canavalia villosa Benth. (Fabaceae, n = 26). Restriction at state level is more noteworthy in the 224 endemic species because 40.6 % are found in one or two states, and 29 % (n = 65 species) do not occupy more than five states (Table 4). The endemic lianas with the greatest geographic distribution are Lonicera pilosa (Kunth) Willd. ex Kunth (Caprifoliaceae; n = 21 states), followed by Funastrum pannosum Schltr. (Apocynaceae), and Nissolia microptera Poir. (Fabaceae), both found in 19 states.

Biomes, vegetation types and altitude. The richness of lianas species is dissimilar among the five recognized biomes of Mexico (Table 5) because the tropical humid forest clearly is the most important, hosting 692 species (80.3 %), followed by tropical seasonally dry forest, temperate forest, humid mountain forest and xerophytic scrubland. Regarding the endemic species, the position of the latter two biomes in terms of total species is not altered; however, the top two places are changed because the tropical seasonally dry forest becomes of highest importance (n = 134 species, 59.8 %), whereas second and third position was taken by temperate forest and tropical humid forest, respectively. The values of richness differ significantly among the biomes, both for the total number of species (χ² = 531.16, d.f. 4, P = 0.001) and the number of endemic species (χ² = 80.55, d.f. 4, P = 0.001).

When species richness is evaluated by vegetation type, the tropical dry forest occupies first place, both for the total number of species (52.1 %) and for that of the endemic species (55.8 %); another similarity between both sets of species is the reduced importance of mangrove, savanna and thorn forest (Table 5). Second place in terms of the total number of species is occupied by the tropical evergreen forest (44.3 %), while for the endemic species this position is held by the oak forest (24.6 %). The nine vegetation types also showed difference for all lianas species (χ² = 836.92, d.f. 8, P = 0.001) and by their number of endemics (χ² = 194.15, d.f. 8, P = 0.001).

Species of lianas are negatively correlated with altitude, with a higher concentration found at lower elevations (Table 6), particularly below 1,500 m elevation, with a statistically significant correlation, both for the total number of species (R= –0.98, P = 0.001) and for endemic species (R = –0.904, P = 0.001).

Discussion

Taxonomic richness. Fifteen families with the greatest taxonomic diversity include 81 % of the species (Table 1). This figure differs from that documented by Gentry (1991a), who found that 26 families of the Neotropics contained 85 % of the species that exhibit a scandent habit. Likewise, there is no coincidence at the level of the entire Mexican flora because the most speciose 15 families include 55 % of the total species (Villaseñor, 2003). Families with more species for Mexico as documented by this last author and for the lianas in the present study indicate a marginal similarity because these groups only share Asteraceae, Fabaceae, Rubiaceae, and Solanaceae, although a subsequent modification of the data of Villaseñor (2003) by Juárez–Jaimes et al. (2007) also incorporated Apocynaceae s.l. within the most diverse Mexican families (position 14). These data suggest that the specialization of climbers has centered in particular family lineages (e.g., Apocynaceae, Convolvulaceae, Malpighiaceae, or Passifloraceae). In addition, it is important to consider that in Apocynaceae and Malpighiaceae, the climbing habit is more frequent compared to other growth forms, such as the trees or shrubs (Juárez–Jaimes et al., 2007; Anderson, 2013).

Considering that the 20 most diverse genera in Mexico include 15 % of the species (Villaseñor, 2004), our results are important given that the 18 more diverse liana genera comprise 38.1 % (n = 328) of the species (Table 2), despite the fact that the proportion of liana genera with only one species is greater (50 %) than that of the entire flora (n = 988; 37 %). The role of Ipomoea is of the greatest importance, and it is no surprise that it is cited as the second most speciose genus among the Neotropical climbing plants (Gentry, 1991a). If the genera of Table 1 are compared with those of the entire Mexican flora (Villaseñor, 2004), only Solanum and Ipomoea are found, occupying the nineth and tenth positions, respectively.

Geographic distribution. For endemic liana genera, our results are comparable with those of Rzedowski (1991a), who calculated an endemism of ±1 %, which is much lower than that obtained for the entire Mexican flora (8 %) by Villaseñor (2004). However, the value of 25.9 % of endemism for liana species is practically half of the percentage that was recently obtained for the whole country (Villaseñor and Ortiz, 2014) but is much closer to that estimated by these authors for the climbers (38 %) or for the vines or woody climbers (15 %) by Rzedowski (1991a). The causes of this important value of endemism may be found in the role that plant communities (e.g., the tropical deciduous forest) or biomes (e.g., the tropical montane humid forest) have played as "ecological islands", as well as the influence of the climate and edaphic substrate in the life cycle and evolution of plants in Mexico (Rzedowski, 1991a, b).

The richness, number of endemics and of the microendemic species that were detected among the lianas of Mexico indicate a very clear inequality among the Mexican states; this relationship is maintained for the seven most important states, regardless of their different sizes (Table 3). One factor that explains these relationships, both for the total number of liana species and for the endemic species, is the proximity of the states (Ibarra–Manríquez et al., 2015). Consequently, the floristic importance at the national level of the states of Chiapas, Guerrero, Jalisco, Michoacán, Oaxaca, and Veracruz is ratified by our results, which support similar conclusions by studies that were conducted on different groups of plants (e.g., Villaseñor et al., 1998; Espejo–Serna et al., 2004a; Juárez–Jaimes et al., 2007; Alcántar–Mejía et al., 2012) or the entire flora (Rzedowski, 1991a, b; Villaseñor, 2003; Villaseñor and Ortiz, 2014).

The lianas found in only one state (Table 4) present much lower values for the total number of species (16.5 %) and endemic species (26 %) than those obtained by Villaseñor (2003) for the entire Mexican flora, with 33 % (n = 8,228 of 24,626 species), and 43 % (n = 5,566 of 12,900), respectively. However, a direct comparison cannot be made because the figures that were presented by this author include sub–specific categories. In addition, as indicated by Villaseñor (2003), these results must be treated with caution as they may be affected by collection bias, thus highlighting the need for a future floristic study that is directed towards a more exact characterization of the geographic distribution of these rare species.

Biomes, vegetation types and altitude. At the level of biomes, the tropical forests have proved to be the most important for liana species, a global pattern that has been indicated in previous studies (Gentry, 1982, 1991a, b; Schnitzer and Bongers, 2002; Schnitzer, 2005). The role of the tropical humid forest is particularly remarkable for its number of species, while the tropical seasonally dry forest stands out for its endemics (Table 5). Contrasting results are seen at the level of the entire flora of Mexico (Villaseñor and Ortiz, 2014) because the temperate forest has the greatest importance both at the level of total richness and of endemic species; in fact, in this latter group of taxa, the tropical humid forest is the least important. These data affirm the significance of conducting particular biogeographic studies for the different growth forms present in Mexico because some can present patterns that are discordant with those that are obtained for the entire flora.

In terms of the hosted liana species, the vegetation types that are recognized in Mexico are of uneven importance (Table 5). In this sense, it is notable that first place for the total number of species and of endemic species is occupied by the tropical deciduous forest, ratifying the ecological and floristic importance of this vegetation type at the global (Olson and Dinerstein, 2002), continental (Lott and Atkinson, 2006) and national scales (e.g., Trejo and Dirzo, 2002; Cué–Bär et al., 2006a, b; Juárez–Jaimes et al., 2007; Rzedowski and Calderón de Rzedowski, 2013). The importance of the oak forest for endemic liana species was not expected because this vegetation type had been considered important for other growth forms, especially herbaceous plants (e.g., Rzedowski, 1978).

However, our results agree with those of Gentry (1991a), Bhattarai and Vetaas (2003) and Jiménez–Castillo et al. (2007) in terms of the negative relationship between the richness of lianas and the altitude. Additional evidence is found in Jiménez–Castillo et al. (2007), who analyzed the data for the lianas in a gradient of tropical vegetation in Mexico and detected the same statistically significant trend. One factor that may explain this result is the sensitivity of lianas to temperatures below the freezing point, which affect their vascular system and impede an efficient transport of water from the root to the crown (Gentry, 1991b; Schnitzer and Bongers, 2002; Schnitzer, 2005). However, the sensitivity of lianas to this factor must be explored in greater detail because other factors that change with altitude could also affect these plants; for example, the total annual precipitation, the seasonality of precipitation or the relative humidity of the air. This last factor has a direct effect on the hydric balance of the plants and the energy availability (Schnitzer and Bongers, 2002; Schnitzer, 2005). Furthermore, it should be considered that lianas in Mexico are by no means scarce in temperate forests (Table 5), justifying the future investigation of the influence of frost and other climatic factors on liana physiology and ecology.

Conclusions

Mexican lianas present patterns of diversity and distribution that must be considered when defining strategies that are directed toward their conservation. The coincidence in the richness, endemism and microendemic taxa at the state level is of particular value, highlighting the relevance of these attributes in the states of Chiapas, Oaxaca, Guerrero, Jalisco and Michoacán (Table 3), where the establishment of Protected Areas is a urgent priority; the same conclusion can be invoked if we analyze the patterns of richness and endemism for the whole flora (Villaseñor, 2003; Villaseñor and Ortíz, 2014). These reserves should have the consent of the different social and political stakeholders that are involved, as well as financial income to guarantee their long–term functioning. From the results that were obtained for the lianas, it is clear that these reserves must include important areas of tropical and temperate forest within the vegetation types that are under protection, especially the tropical deciduous forest, tropical montane cloud forest and oak forest. The high beta diversity that is exhibited by lianas is concordant with that exhibited by the flora (Villaseñor, 2003; Pérez–García et al., 2005; Trejo, 2005) and fauna (Rodríguez et al., 2003; Flores–Villela et al., 2005), and their complementarity should be considered during these conservation exercises, especially in terms of the endemic species.

The data from the present study indicate that lianas play a fundamental role in the taxonomic diversity of the flora of Mexico, which is one of the greatest worldwide. Botanical exploration is an important task that must still be completed, particularly for those biological groups underrepresented in plant inventories and collections mainly by the difficulties inherent in their biological form, such as lianas, in which many species represent microendemics, that are currently being discovered and named (e.g. Cuevas–Guzmán and Núñez–López, 2015; Linares, 2015). However, Ibarra–Manríquez et al. (2015) indicated that the conservation status of lianas in Mexico is of concern. For this reason, it is hoped that our contribution can promote the development of studies that further the knowledge of the biogeography, ecology and systematic of the lianas in this country, providing broader information with which to prioritize efforts to ensure the future conservation of lianas in the ecosystems that they occupy.

Acknowledgments

This study formed part of the postdoctoral research project of Pablo Carrillo–Reyes "Diversity and biogeography of the Mexican lianas", from 2011–2012, which was funded by the Consejo Técnico de la Investigación Científica (oficio CJIC/CTIC/2318/2010) of the Universidad Nacional Autónoma de México (UNAM). Francisco Javier Rendón–Sandoval was a Master's student in the Posgrado de Ciencias Biológicas of UNAM, for which he gratefully received a grant from the Consejo Nacional de Ciencia y Tecnología (CONACyT). Thanks to Heberto Ferreira Medina, Alberto Valencia García and Atzimba López Maldonado for their support with data base and computer programs. Finally, we thank José Luis Villaseñor Ríos, Luis Enrique Eguiarte Frunz and an anonymous reviewer for important comments on the manuscript.

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