Tree and tree-like species of Mexico: Apocynaceae, Cactaceae, Ebenaceae, Fagaceae, and Sapotaceae

Abstract

Trees or tree-like plants are defined here broadly as perennial, self-supporting plants with a total height of at least 5 m, without considering ascending leaves or inflorescences, and with 1 or several erect stems with a diameter of at least 10 cm. In this third contribution of the taxonomic compilation of Mexico's native tree species, 271 species are presented: 27 in the family Apocynaceae (26% endemic), 63 in the Cactaceae (79%), 17 in the Ebenaceae (35%), 123 in the Fagaceae (60%), and 41 in the Sapotaceae (22%). Several cactus genera are endemic to Mexico, notably Neobuxbaumia with 10 species and heights up to 22 m. The oak genus Quercus with 122 species is the most species-rich genus of Mexican trees. Several species are reported to reach heights of 60 m (Aspidosperma desmanthum, Quercus benthamii, Q. corrugata, and Manilkara chicle). All species are listed in an appendix, including the original publication, references of taxonomic revisions, in some cases synonyms, existence of subspecies or varieties, maximum height in Mexico, and the indication if the species is endemic to Mexico.

Resumen

Las plantas arbóreas o arborescentes se definen en este trabajo en un sentido amplio como plantas perennes que se pueden sostener por sí solas, con una altura total de al menos 5 m, sin considerar hojas o inflorescencias ascendentes y con 1 o varios tallos erectos de un diámetro de al menos 10 cm. En esta tercera contribución de la recopilación de las especies arbóreas nativas de México, se presentan 271 especies: 27 de la familia Apocynaceae (26% endémicas), 63 de Cactaceae (79%), 17 de Ebenaceae (35%), 123 de Fagaceae (60%) y 41 de Sapotaceae (22%). Algunos géneros de Cactaceae son endémicos en México, notablemente Neobuxbaumia con 10 especies y alturas de hasta 22 m. Con 122 especies, Quercus es el género arbóreo más diverso en especies de México. Algunas especies se registran con alturas de hasta 60 m (Aspidosperma desmanthum, Quercus benthamii, Q. corrugata y Manilkara chicle). Todas las especies se enlistan en un apéndice que incluye el nombre científico, los datos de su publicación original, referencias de revisiones taxonómicas, en algunos casos sinónimos, la existencia de subespecies o variedades, la altura máxima en México y la indicación de si la especie es endémica de México.

Introduction

In Ricker and Hernández (2010), and slightly extended in Ricker, Hernández, Sousa, and Ochoterena (2013), trees or tree-like plants were defined broadly as perennial, self-supporting plants with a total height of at least 5 m, without ascending leaves or inflorescences, and with 1 or several erect stems with a diameter of at least 10 cm, measured at 1.3 m above the ground level, or measured above buttresses if these are present. A tree or tree-like species contains individuals with tree characteristics at least somewhere in its geographic range, but not necessarily everywhere. After discussing the tree definition and emphasizing the need for an updated taxonomic list of Mexico's tree species, Ricker and Hernández (2010) presented 170 species of gymnosperms, monocotyledons, and tree ferns. In Ricker et al. (2013) the work was continued with 619 species in the species-rich plant families Asteraceae, Leguminosae, and Rubiaceae. The Leguminosae, with 449 tree species in its 3 subfamilies, is the most diverse tree-species family in Mexico. In the current paper, the work is continued with 5 plant families: Apocynaceae, Cactaceae, Ebenaceae, Fagaceae, and Sapotaceae.

Materials and methods

The list of species is presented in an appendix that provides the scientific names of the tree species, as defined in Ricker et al. (2013), with original publication, references of recent taxonomic revisions, in some cases synonyms, existence of subspecies or varieties, maximum height in Mexico, and the indication if the species is endemic to Mexico. Only species native to Mexico were included in the appendix.

A taxonomic description of the families treated here can be found in Heywood, Brummitt, Culham, and Seberg (2007). The Apocynaceae, Ebenaceae, and Sapotaceae were revised in the “Flora Mesoamericana” series, which includes in Mexico the states of Tabasco, Chiapas, Campeche, Quintana Roo, and Yucatán (Davidse, Sousa, Knapp, Chiang, & Barrie, 2009). The Sapotaceae were revised by Pennington (1990) already in a “Flora Neotropica” volume, which includes all of Mexico. Furthermore, a checklist of Mexican species was published for the Apocynaceae by Juárez-Jaimes, Alvarado-Cárdenas, and Villaseñor (2007), and for the Fagaceae by Valencia (2004). For the cactus family, the taxonomic framework of Anderson (2001), and Hunt (2006a, 2006b, 2016) is adopted. In addition to compiling the tree species for each family, different taxonomic viewpoints had to be considered and synthesized for a number of species; for example, the species of Stemmadenia were synonymized with Tabernaemontana (Alvarado-Cárdenas & Juárez, 2012; Simões, Endress, & Conti, 2010), and Cascabela was recognized as a genus different from Thevetia (Alvarado-Cárdenas & Ochoterena, 2007; Alvarado-Cárdenas & Soto, 2014:163).

For any species with doubts, the specimens in the National Herbarium of Mexico (MEXU) were checked for growth form, height, and trunk diameter. In some cases, the endemism status in the herbarium was also verified, if it was not clear from the literature. The heights reported in the appendix refer to those maximum heights reached by the species somewhere in Mexico. Exceptional height values for Mexico are given in parenthesis. Endemism refers to the species distribution being restricted to Mexico, as far as currently known.

Most herbarium specimens contain growth form and height in their labels, but generally trunk diameters are not given. This made it sometimes necessary to infer trunk diameters allometrically from height. For example, if a specimen was given with 4 m height and 6 cm trunk diameter, and another specimen was given with 8 m without information on trunk diameter, linear extrapolation indicates that it could have a diameter of around 12 cm (8 × 6/4), though this is only a rough approximation. Furthermore, a tree of 10 m or more can generally be assumed to reach a minimum trunk diameter of 10 cm, unless contrary information is given. Where doubts remained about the trunk diameter reaching at least 10 cm, the species was not included. Four oak species are known only from the original descriptions and without height information: Quercus edwardsiae C. H. Muller, Quercus ghiesbreghtii M. Martens et H. G. Galeotti, Quercus ignasiensis C. H. Muller, and Quercus rekonis W. Trelease. As there also exist small (non-tree) species of Mexican oaks, these 4 species were not included. Taxonomic literature for the recognized species names is cited in the appendix. The authors of species names and original publications were verified in Tropicos (www.tropicos.org). Synonyms are mentioned here only in cases when they reflect diverging opinions among different taxonomic specialists. For mentioned synonyms, species’ author names are not given here, but can be found for example in Tropicos.

Results

The results for 271 species in 29 genera are detailed in the appendix, and summarized in Table 1. Of the 271 species, 45% pertain to the Fagaceae, followed by 23% in the Cactaceae, 15% in the Sapotaceae, 10% in the Apocynaceae, and 6% in the Ebenaceae. The genus with most tree species is Quercus (122 species, Fagaceae), followed by Sideroxylon (24, Sapotaceae), Diospyros (17, Ebenaceae), and Stenocereus (14, Cactaceae).

Table 1.

Summary of the data in Appendix.

Family	Species	Endemic species	Tallest species	Genera	Endemic genera	Genera with most tree species
Apocynaceae	27	7 (26%)	Aspidosperma desmanthum (60 m)	7	None	Tabernaemontana (9 species)
Cactaceae	63	50 (79%)	Pachycereus pringlei (25 m), Neobuxbaumia mezcalaensis (22 m)	14	Cephalocereus, Isolatocereus, (Lophocereus)^a Neobuxbaumia Polaskia	Stenocereus (14), Opuntia (12)
Ebenaceae	17	6 (35%)	Diospyros nigra (35 m)	1	None	Diospyros (17)
Fagaceae	123	74 (60%)	Quercus benthamii, Q. corrugata, Q. cortesii, Q. skinneri (all 60 m)	2	None	Quercus (122)
Sapotaceae	41	9 (22%)	Manilkara chicle (60 m)	5	None	Sideroxylon (24)
Total of all families	271	146 (54%)		29	4 (5)

a

Lophocereus schottii slightly crosses the border into Arizona (USA).

There are species endemic to Mexico in all 5 families. The endemism rate is 54% for all species combined (146/271), with particularly high rates in the Cactaceae (79%) and the Fagaceae (i.e., Quercus: 60%). Notably, there are 4 endemic genera, all found in the Cactaceae (Cephalocereus, Isolatocereus, Neobuxbaumia, and Polaskia); a fifth cactus genus (Lophocereus) crosses slightly the border with the United States into Arizona. The most species-rich genus of these 5 is Neobuxbaumia with 9 species. With heights up to 22 m, it is also among the cactus genera with the tallest individuals, together with Pachycereus (Table 1). The tallest trees (60 m) are found in the species Aspidosperma desmanthum (Apocynaceae), Quercus benthamii, Q. corrugata, Q. cortesii, and Q. skinneri (Fagaceae), as well as in Manilkara chicle (Sapotaceae). Quercus corrugata is reported to reach a trunk diameter of up to 4 m (le Hardÿ de Beaulieu, Lamant, Timacheff, Jablonski, & Spoelberch, 2006). An arborescent cactus species of impressive size is Pachycereus weberi, with individuals up to 15 m high and 2 m in stem diameter (Hernández, 2006).

Discussion

There is a great need from scientists, foresters, naturalists, and conservationists for an updated checklist of tree species for Mexico. While the exact number of all Mexican tree species that reach at least 5 m height and 10 cm trunk diameter is unknown, the 271 species reported here represent probably close to 10% (see discussion in Ricker & Hernández, 2010). For the 5 plant families treated, the reported diversity corresponds to the total Mexican diversity, trees and non-trees, as follows.

Apocynaceae: the 27 Mexican tree species in the appendix represent only 7% of the reported 385 Mexican species in the Apocynaceae (Juárez-Jaimes et al., 2007). Despite the fact that the family does not include a high proportion of tree species, the members of this family represent some of the typical tree elements in tropical forests (Juárez-Jaimes et al., 2007; Rzedowski & Rzedowski, 1998, 2013). Furthermore, Aspidosperma desmanthum is one of the tallest tree species in Mexico.

Cactaceae: there are 560 Mexican species of Cactaceae (Hernández & Gómez-Hinostrosa, 2011), so the 63 tree-like species reported here represent 11% of the total number of Mexican Cactaceae. Remarkable is the high rate of endemism among tree-like cactus species (79%), which is similar to the endemism rate of 78% of all Mexican members of the family (Hernández & Godínez, 1994).

Ebenaceae: the persimmon family has 19 Diospyros species in Mexico, of which 2 (D. intricata and D. reinae) are not trees according to our definition, so that the number of tree species is 89% of the total number of Mexican Ebenaceae. The genus adapts to a variety of habitats; while D. juruensis is generally a rare species of tropical wet forests from Mexico to Brazil (Wallnöfer, 2012), D. texana extends from Mexico into Texas, being in some areas a highly dominant scrub species (Wallnöfer, 2011).

Fagaceae: while there is only 1 species of Fagus (beech) in Mexico, out of 10 species worldwie (Govaerts & Frodin, 1998:142), we report 122 Quercus species. The 123 tree species represent 76% of the 162 species in the Mexican Fagaceae (Govaerts & Frodin, 1998; Valencia, 2004).

Sapotaceae: the 41 reported tree species represent 95% of the 43 Mexican species; Pennington (1990) reports that in addition only Sideroxylon eriocarpum and S. verruculosum grow as shrubs smaller than 5 m in height. The family is typically found in lowland wet forests.

The oak diversity in Mexico is remarkable. Govaerts and Frodin (1998:201) report 531 Quercus species worldwide, of which about 30% are found in Mexico. The distribution of the oak species in Mexico is discussed in Nixon (1993) and Valencia (2004). The genus is found throughout Mexico at elevations from sea level up to 3,650 m (Q. laurina in the state of Hidalgo); the states of Oaxaca and Jalisco are particularly diverse in oak species. With 122 species representing trees, Quercus is clearly the most species-rich genus of all Mexican trees, followed by Lonchocarpus (Leguminosae Papilionoideae) with 67 species (Ricker et al., 2013). The only hybrid species is Quercus × dysophylla. In addition, the endemism rate of 60% for the Mexican oak tree species is also notably high.