Tree and tree-like species of Mexico: Asteraceae, Leguminosae, and Rubiaceae

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 ascending leaves or inflorescences), and with one or several erect stems with a diameter of at least 10 cm. We continue our compilation of an updated list of all native Mexican tree species with the dicotyledonous families Asteraceae (36 species, 39% endemic), Leguminosae with its 3 subfamilies (449 species, 41% endemic), and Rubiaceae (134 species, 24% endemic). The tallest tree species reach 20 m in the Asteraceae, 70 m in the Leguminosae, and also 70 m in the Rubiaceae. The species-richest genus is Lonchocarpus with 67 tree species in Mexico. Three legume genera are endemic to Mexico (Conzattia, Hesperothamnus, and Heteroflorum). The appendix lists all species, including their original publication, references of taxonomic revisions, existence of subspecies or varieties, maximum height in Mexico, and endemism status.

Resumen

Las plantas arbóreas o arborescentes se definen aquí 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 uno o varios tallos erectos de un diámetro de al menos 10 cm. Continuamos nuestra recopilación de un listado actualizado de todas las especies arbóreas nativas de México con las familias dicotiledóneas Asteraceae (36 especies, 39% endémicas), Leguminosae con sus 3 subfamilias (449 especies, 41% endémicas) y Rubiaceae (134 especies, 24% endémicas). Las especies más altas alcanzan 20 m en Asteraceae y 70 m tanto en Leguminosae como en Rubiaceae. El género con el mayor número de especies es Lonchocarpus con 67 de tipo arbóreo en México. Tres géneros de leguminosas son endémicos de México (Conzattia, Hesperothamnus y Heteroflorum). El apéndice proporciona todas las especies, incluyendo los datos de su publicación original, referencias de revisiones taxonómicas, la existencia de subespecies o variedades, la altura máxima en México y su estatus de endemismo.

Introduction

We continue our compilation of trees and treelike plants from Ricker and Hernández (2010). In that publication we discussed the motivation and need for an updated inventory of Mexico's tree species after Standley's work in 1920-26 about trees and shrubs of Mexico. For our purposes we defined trees or tree-like plants broadly as perennial, self-supporting plants with a total height of at least 5 m (without ascending leaves or inflorescences), and with one 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. Tree-like (woody) species that are smaller than 5 m, or present a diameter of less than 10 cm, could be distinguished as “shrubs” or “dwarf trees”. Plants that are higher than 5 m, but do not present a diameter of 10 cm, could be distinguished as “bamboo-type plants”. These species are not included in our compilation.

Ricker and Hernández (2010) compiled 170 species of gymnosperms (Cupressaceae, Pinaceae, Podocarpaceae, Taxaceae, Zamiaceae), monocotyledons (Agavaceae, Arecaceae, Dracaenaceae, Nolinaceae, Poaceae), and tree ferns (Cyatheaceae, Dicksoniaceae). Here we start with the dicotyledonous plant species, which represent by far the mayority of trees in Mexico, treating first 3 plant families known to be species-rich in Mexico: the Asteraceae, Leguminosae, and Rubiaceae. Indeed, the 4 families worldwide with most plant species are the Orchidaceae, Asteraceae, Leguminosae, and Rubiaceae (Heywood et al., 2007: 284). The Orchidaceae presents no tree species, and in the Asteraceae herbaceous and shrubby species are dominant, making the Leguminosae the most likely candidate of being the most species-rich tree family worldwide and also in Mexico. Taxonomic caracter states for the families are given for example in Heywood et al. (2007), and for the Leguminosae in Lewis et al. (2005). To be mentioned are also Cronquist (1981) for the 3 families (he treats the Leguminosae in 3 separate families), and Robbrecht (1988) for the Rubiaceae.

The Asteraceae of Mexico, including some tree species of this publication, have been treated by Turner (1997, 2007, 2009), but the series is not completed yet. The legume trees of Mexico were treated in Sousa et al. (2001; 2003); in that work plants reaching a height of 3 m were considered (instead of 5 m here), without regard to a minimum trunk diameter (10 cm here). The present compilation is based on Sousa et al (2001; 2003), but most species were screened now in the National Herbarium of Mexico (MEXU) for verifying height and diameters, whenever available. In addition, many taxonomic changes and new references are included.

For the family Rubiaceae, Borhidi (2006) published his book on the species of this family in Mexico. For many genera, however, there is discussion and diverging opinions if Borhidi's system reflects evolutionary relationships and corresponding scientific names accurately, such as in the Rondeletia (Arachnothryx) complex (Lorence, 1991: 135–137; Rova et al., 2009). Often we compared with Lorence (1999), and follow here for southern Mexico especially the new Flora Mesoamericana treatment for the family Rubiaceae (Burger and Taylor, 2012; Delprete and Persson, 2012; Lorence, 2012b-r; Lorence and Taylor, 2012; McDowell, 2012; Ochoterena, 2012a-c; Pacheco and Lorence, 2012; Taylor, 2012a-k; Taylor and Lorence, 2012a-d). We do, however, cite differing opinions about scientific names.

Materials and methods

The appendix provides the scientific names of the tree species according to our definition in the 3 families, with original publication, references of recent taxonomic revisions, in some cases synonyms, existence of subspecies or varieties, maximum height in Mexico, and indication if endemic to Mexico.

Family names follow Heywood et al. (2007). For the Asteraceae and Leguminosae there are alternative family names (Compositae and Fabaceae, respectively). We generally use the nomenclature for standard families, which in case of the Leguminosae would be “Fabaceae”. As discussed in Lewis et al. (2005: 1–2), however, for the Leguminosae there are 2 problems: 1), the term “Fabaceae” is ambigous, because it may refer to the whole family or only to the subfamily Papilionoideae, and using “Leguminosae” avoids confusion. 2), there has not been an international consensus about the rank of the 3 subfamilies in the Leguminosae. In particular Cronquist (1981) in his book of the families of flowering plants distingishes 3 distinct families (Caesalpiniaceae, Fabaceae, and Mimosaceae), but Lewis et al. (2005: 1) mention also more recent authors. Lewis et al. argue in support of the Leguminosae being one monphyletic family, and not giving each subfamily independent family status, because according to them the Leguminosae is clearly distinguishable from ‘nearest neighbor families’ (Polygalaceae, Quillajaceae, and Surianaceae); there is only discussion about subdividing further the subfamily Caesalpinioideae.

Subfamilies do also exist in the Asteraceae and Rubiaceae, but there is not a discussion about their rank comparable to the Leguminosae, and therefore we present subfamilies only in the latter case. Our approach to use for the Leguminosae the nomenclature for a superfamily (as an exception) is also the one taken in Heywood et al. (2007).

For the Asteraceae, an initial list of species that could fit our definition of a Mexican tree species was compiled from Grandtner (2005), who generally presents by far an overestimate of tree species (as defined by us), and includes synonyms as supposedly valid species. A second source was Parker (2008), a book which is relatively detailed and accurate for southern Mexico. For the Leguminosae we started off with Sousa et al. (2001; 2003), and for the Rubiaceae with Borhidi (2006) and Parker (2008). Subsequently we added specialized literature depending on the genera.

The heights in the appendix refer to those maximum heights reached by the species anywhere in Mexico. Exceptional values for Mexico are given in parenthesis, meaning that we detected a discontinuity of heights, separating a few “outliers” from the majority of specimens. Endemism refers to the species distribution being restricted to Mexico, as far as is currently known. For almost all species we checked the specimens in the National Herbarium of Mexico (MEXU) for growth form, height, and if available trunk diameter. In some cases, we had to check also the endemism status. For some species there were recent revisions in the literature, which made it unecessary to check specimens. Most specimens contain growth form and height in their labels, but frequenty trunk diameters are not given. This made it often 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, we extrapolated linearly and inferred that it could have a diameter of around 12 cm (8 × 6/4), though this is a rough approximation. Furthermore, a tree of 10 meters or more can generally be assumed to reach a trunk diameter of 10 cm, unless contrary information about growth form is given.

Particularily in the family Asteraceae it was notorious in multiple species to have many specimens representing small shrubs, and only a few specimens being trees according to our definition (often in Guerrero in the case of Asteraceae). We provide comments in that case, such as “frequently smaller”, as in Clibadium arboreum. There are also cases, where the species is usually a liana and only rarely a tree, such as in Machaerium pittieri (Leguminosae-Papilionoideae). In cases where doubts remained about the trunk diameter, we tended not to include the species in our list, such as in the case of large but “decumbent shrubs.”

Only species native in Mexico were included in our compilation. Some famous but introduced tree species are not included in our list, such as Delonixregia (Leguminosae, “framboyan”, ornamental from Madagascar), Tamarindus indica (Leguminosae, “tamarindo”, originally from Africa), and Coffea arabica (Rubiaceae, “coffee”, originally from Ethiopia, Sudan, and the Arabian Peninsula; see Lorence, 2012a: 60–61). Lesser kown tree species that are introduced and possibily naturalized, but are not mentioned further, are Albizia carbonaria, Albizia lebbeck, Bauhinia variegata, Cassia fistula, Pterocarpus officinalis (all Leguminosae), Cinchona pubescens, and Morinda citrifolia (Lorence and Taylor, 2012: 147) (both Rubiaceae).

Taxonomic literature for the recognized species names is cited in the appendix. In order to update the taxonomic nomenclature, sections of the list were reviewed by several specialists (see acknowledgments). The authors of species names and original publications were double-checked in TROPICOS (www.tropicos.org). Species' author names not mentioned here, such as for synonyms, can be found in TROPICOS. We provide synonyms only in cases when they are very recent and/or cause diverging opinions among different taxonomic specialists, and we had to decide which name to follow or in general when it is important to avoid confusion. The existence of many other synonyms can be found in TROPICOS. In case of doubts about the existence of a separate species we were conservative: For example, in the Rubiaceae and with the evidence at hand we consider Arachnothryx lineolata to be a synonym of Chomelia brachypoda, and Randia serboi to be a synonym of Randia tetracantha.

Results

Table 1 summarizes the information given in the appendix. The total number of tree species listed is 619, in 141 genera. Of the 619 species, 73% pertain to the Leguminosae, followed by 22% in the Rubiaceae, and (only) 6% in the Asteraceae. Within the Leguminosae, the largest subfamily is the Papilionoideae with 46% of the 449 species, followed by the Mimosoideae with 39%, and the Caesalpinioideae with 16%. The genus with most tree species is Lonchocarpus (67 species), followed by Inga (34) and Acacia (32) (all Leguminosae).

Table 1.

Summary of the data in the appendix

Family and subfamily	Species	Endemic species	Tallest species	Genera	Endemic genera	Genera with most tree species
Asteraceae	36	14 (39%)	Lepidaploa polypleura (20 m)Montanoa hexagona (20 m)Montanoa revealii (20 m)Telanthophora uspantanensis (20 m)	20	None	Critoniopsis (6)Verbesina (4)
Leguminosae Caesalpinioideae	71	26 (37%)	Dialium guianense (65 m)Schizolobium parahyba (50 m)Bauhinia cookii (40 m)Hymenaea courbaril (40 m)	21	Conzattia, Heteroflorum	Caesalpinia-Poincianella^1Senna (12)Bauhinia (11)
Leguminosae Mimosoideae	173	59 (34%)	Albizia adinocephala (65 m)Albizia leucocalyx (60 m)Enterolobium cyclocarpum (60 m)	21	None	Inga (34)Acacia (32)Leucaena (17)Mimosa (16)
Leguminosae Papilionoideae	205	100 (49%)	Lonchocarpus castilloi(70 m)Myroxylon balsamum (70 m)Vatairea lundellii (70 m)	37	Hesperothamnus	Lonchocarpus (67)Erythrina (19)Dalbergia (17)
Total of Leguminosae	449	185 (41%)		79	3
Rubiaceae	134	32 (24%)	Blepharidium guatemalense (70 m)Chione venosa (40 m)Guettarda macrosperma (40 m)Simira salvadorensis (40 m)	42	None	Arachnothryx (23)Randia (18)Psychotria (12)
TOTAL of all families:	619	231 (37%)		141	3

1

The genus Caesalpinia is currently being taxonomically reorganized: our list contains 12 Caesalpinia species and 9 Poincianella species; however, 6 Caesalpinia species may be transferred formally to Poincianella in the future, and another 5 Caesalpinia species may be transferred to Coulteria and Tara (see our appendix). Eventually, there may only be one true Caesalpinia tree species left of our list (Caesalpinia pulcherrima), and 15 Poincianella species.

The 449 tree species in the Leguminosae represent about 24% of the approximately 1 850 legume species found in Mexico (Sousa and Delgado, 1993; Sousa et al., 2001: 339). Borhidi (2006: 9) calculates 585 species for the Rubiaceae in Mexico, so that the 134 tree species would represent 23% of all species. On the other hand, the 36 tree species in the Asteraceae represent only about 1.3% of the approximately 2 700 species of Mexican Asteraceae (Turner and Nesom, 1993: 559).

The endemism rate is 37% for the species of all 3 families (231/619). The highest rate is found in the subfamily Papilionoideae of the Leguminosae with 49%. Notably, there are 3 endemic genera, all found in the Leguminosae (Conzattia, Hesperothamnus, and Heteroflorum).

Discussion

The number of 623 legumes species in Sousa et al. (2001; 2003), with a height of at least 3 m, decreased here to 449 tree species with a height of at least 5 m and a trunk diameter of at least 10 cm (a reduction of 28%). Apart of deleting from the list those species that did not comply with our size definition, there were many additional changes over the last decade, such as changes of species concepts (e.g., in the case of Lonchocarpus longistylus), resurrection of formerly published names (e.g., Poincianella acapulcensis), species transfers between genera (e.g., Caesalpinia species to 3 other genera; Lonchocarpus unifoliolatus to Muellera unifoliolata), and 30 new species published after 2002 (without considering new combinations or rank changes): Bauhinia wunderlinii, Caesalpinia oyamae, Heteroflorum sclerocarpum (all Caesalpinioideae), Inga appendiculata, I. lactifera, (Mimosoideae), Andira jaliscensis, Dalbergia longepedunculata, D. luteola, D. modesta, D. rhachiflexa, D. ruddae, Dalea schiblii, Diphysa yucatanensis, L. barbatus, L. berriozabalensis, L. brenesii, L. congestiflorus, L. foveolatus, L. isthmensis, L. latimarginatus, L. martinezii, L. michoacanicus, L. multifoliolatus, L. plicatus, L. septentrionalis, L. sylvicola, L. tuxtepecensis, L. vittatus, L. wendtii, and Platymiscium calyptratum (Papilionoideae).

We detected 7 very tall species in the Leguminosae, with maximum heights of 60 to 70 m (see Table 1), although such heights were only exceptionally reported in the herbarium specimens. These exceptional heights were often found in specimens from Chiapas, though it is not clear if this is due to exceptional site conditions in Chiapas, or because such big trees had not (yet) been cut down there at the time of collection. The tallest tree that we found in the Rubiaceae was a specimen of Blepharidium guatemalense (Rubiaceae) with 70 m, reported in Chiapas (Marqués de Comillas). In comparison, the tallest Asteraceae species were only reported with 20 m (Table 1).

We will provide an integral discussion about Mexico's tree species diversity, including a comparison with tree species diversity in other countries, once our compilation of all the tree species according to our definition is complete.

Acknowledgements

The quality of taxonomic compilations, such as in the present article, depends frequently on the input of taxonomic specialists. We are grateful for revision and comments from José Luis Villaseñor (Asteraceae), Gloria Andrade (Lysiloma), Rosaura Grether (Mimosa), Bente Klitgaard (Platymiscium, Pterocarpus), Jeny Solange Sotuyo, and Gwil P. Lewis (Caesalpinia, Coulteria, Poincianella, Tara), Lourdes Rico (Acacia), Rafael Torres (Bauhinia), and David Lorence (Rubiaceae). Walter E. Parra helped with the compilation of an initial species list. Furthermore, the final manuscript was read by Esteban Martínez Salas and Clara Ramos Alvarez. Rosaura Grether is from the Universidad Autónoma Metropolitana, Mexico City; Bente Klitgaard, Gwil P. Lewis, and Lourdes Rico are from the Royal Botanic Gardens, Kew, U.K.; David Lorence is from the National Tropical Botanical Garden, Hawai, USA; the other mentioned colleagues are from the Instituto de Biología. Finally, we thank Guillermo Ibarra-Manríquez as the journal's Associate Editor and two referees for their observations.