Introduction

The genus Dalbergia has a pantropical distribution and comprises ca. 250 species (^{Vatanparast et al., 2013}), 27 of which are distributed in the Mesoamerican region (^{Linares & Sousa, 2007}; ^{Ricker et al., 2013}; ^{Sousa et al., 2001}; ^{Standley & Steyermark, 1946}). Timber obtained from some species of the genus is known as rosewood, which has a high economic value for its beauty, durability and excellent mechanic and acoustic properties (^{Richter et al., 1996}). According to Traffic (^{Jenkins et al., 2012}) about 20 species of Dalbergia around the world are traded internationally for tonewood (for guitars, marimbas and xylophones, among other musical instruments), luxury furniture and luxury consumer items. In addition, the heartwood of some species has been used in traditional medicine, as they have antibacterial, antifungal, antioxidant and cytotoxic properties (^{Hamburger et al., 1988}; ^{Lianhe et al., 2011}; ^{Pérez-Gutiérrez & García-Báez, 2013}; ^{Rutiaga-Quiñones et al., 1995}). Moreover, the pigments obtained from the heartwood of Dalbergia congestiflora Pittier have potential for food and cosmetics industry as colorants (^{Barragán-Huerta et al., 2004}).

In Mexico, several species of Dalbergia have been traditionally used to make furniture, musical instruments, knife handles, and art crafts among other objects (^{Díaz-Gómez & Huerta-Crespo, 1986}; ^{Guridi & García-López, 1996}). However, from 2010 onwards, the demand for Dalbergia as a source of timber increased worldwide driven mainly by the expansion of the Chinese market (^{Basik, 2015}). As a consequence, enormous amounts of wood have been illegally extracted from the wild, seriously impacting natural populations. According to the Convention on National Trade in Endangered Species of Wild Fauna and Flora (CITES), between 2007 and 2012, China imported a total of 10,662 m³ of rosewood from Mexico (^{CITES, 2013}). Since then, the Mexican Environmental Protection Agency (Procuraduría Federal de Protección al Ambiente-Profepa) has detected several illegal shipments of Dalbergia wood to third countries. In addition to the problems of overexploitation and illegal trade, Dalbergia species in Mexico are distributed in highly endangered ecosystems such as tropical deciduous forests, tropical subdeciduous forests, tropical evergreen forests and cloud forests, among others. These 4 types of vegetation have been particularly affected by deforestation, mainly to establish agricultural and ranching fields (^{Dirzo & García, 1992}; ^{Gual-Díaz & Rendón-Correa, 2014}; ^{Hughes et al., 2000}; ^{Miles et al., 2006}).

While important taxonomic contributions have enriched our knowledge on the genus Dalbergia such as the pioneering works of ^{Pittier (1922)} and ^{Standley (1922)}, some national checklists (^{Ricker et al., 2013}; ^{Sousa et al., 2001}, ²⁰⁰³), regional floras such as Flora of Guatemala (^{Standley & Steyermark, 1946}) and Flora Novo-Galiciana (^{McVaugh, 1987}) as well as the publication of new species in different regions of the country (^{Linares & Sousa, 2007}; ^{Rzedowski & Guridi-Gómez, 1988}), the lack of an updated checklist of the Dalbergia species in Mexico has stalled the regulation and management of these species, especially of those subject to exploitation. This work compiles, to date, the taxonomic and conservation information for all species within a country rich in Dalbergia species; it provides an annotated checklist and an identification key for the Mexican species of Dalbergia, and makes available the information about their life form, distribution, types of vegetation in which they are found, common names, current risk status under the Mexican legislation (NOM-059-Semarnat-2010; ^{Semarnat, 2010}), the IUCN Red List, as well as the species listed in the CITES Appendices.

Materials and methods

We performed a bibliographic review for all Dalbergia species described for Mexico as well as in areas with phytogeographic affinity and revised all floristic contributions and taxonomic treatments published to date as well as the protologues for all species distributed in Mexico. We also reviewed ca. 4,000 herbarium specimens deposited in the National Herbarium of Mexico (MEXU) as well as duplicates of Mexican species deposited in the California Academy of Sciences (CAS), Dudley Herbarium, Stanford University (DS), Field Museum of Natural History (F), Escuela Agrícola Panamericana (EAP), Missouri Botanical Garden (MO), New York Botanical Garden (NY) and University of California (US) herbaria. We also revised herbarium material from Central America and northern South America. With this information, we compiled a list of the native Mexican species of Dalbergia (Appendix 1). Throughout the paper, we discuss the relevant taxonomic opinions that differ from those in published literature and databases. Our checklist includes the scientific name, its authority, as well as the protologue. We revised the type material for each Mexican species, as well as their associated literature, in order to better circumscribe species with their related names, considering morphological, phenological, and ecological aspects. We include all previously published synonyms for Mexican species, except those names which are in conflict with the species we recognize for the country (e.g., Dalbergia cubilquizensis (Donn. Sm.) Pittier as a synonym of D. tucurensis Donn. Sm. - TROPICOS). Information about life form, maximum height, vegetation types, altitude, and common names come from literature and herbarium specimens, whereas distribution is exclusively based on herbarium specimens. We only use curated specimens as the base for distribution as some of the information reported on the literature cannot be verified; on the other hand, herbarium specimens constitute primary information sources. We also provide distribution maps for each species based on ca. 1,000 herbarium specimens of MEXU; localities without coordinates were geo-referenced. Additionally, we include current risk of extinction status for each Mexican Dalbergia species according to the NOM-059-Semarnat-2010, the IUCN Red List, and the species regulated under CITES. Finally, we indicate if the species is endemic to Mexico.

Results

In Mexico, there are 20 species of Dalbergia, 5 of which (20%) are endemic. Most species are trees reaching 5 meters or more; 4 species are shrubs or lianas (D. brownei (Jacq.) Schinz, D. ecastaphyllum (L.) Taub., D. monetaria L. f. and D. tabascana Pittier); D. glabra (Mill.) Standl. is the only species that can be a liana, shrub or tree lower than 5 m high and with scandent branches. Below, we provide a key for the identification of the Dalbergia species distributed in Mexico, as well as a checklist of the Dalbergia species of Mexico (Appendix 1) and their corresponding distribution maps (Appendix 2).

Key to the Mexican species of Dalbergia.

1. Lianas and scandent shrubs or if trees less than 5 m high and with scandent branches.................................................................................................................................................2

1. Erect trees 5 m high or more, never with scandent branches.................................................................................................................................................6

2. Leaflets less than 4 cm long, mostly less than 2 cm long.......................................................................................................................................................3

2. Leaflets more than 4 cm long, most of them more than 5 cm long.......................................................................................................................................................4

3. Flowers 5-6 mm long; dense inflorescences, mostly axillary, pedicels 1-2 (-2.5) mm long; fruits linear-oblong or oblong, 4-10.5 × 0.9-1.2 (-1.4) cm, attenuate in the apex, reticulate veined, thin and flexible; terminal leaflet oblong; inhabiting open or rocky places, never in swamps or flooded places................................................................................................................................................. Dalbergia glabra

3. Flowers (7-) 8-9 (-11) mm long; sparse inflorescences, mostly teminal, pedicels 3-5 mm long; fruits falcate or obliquely oblong, (1.4-) 1.5-4.6 × (0.7) 0.9-1.1 cm, normally truncate at the apex, not reticulate veined, thickened and somehow woody around the seeds; terminal leaflet mostly obovate; inhabiting permanent or seasonally flooded places.....................................................................................................................................................Dalbergia tabascana

4. Leaflet 1, densely strigose, discolorous; ovary villose or sericeous; fruit sparsely strigulose when mature.....................................................................................................................................................Dalbergia ecastaphyllum

4. Leaflets 1-7, sparsely strigulose, normally concoloured; ovary glabrous or ciliate in the upper margin; fruit glabrous, shining when mature...............................................................................................................................................5

5. Leaflets 1-3, commonly subcordate or truncate at the base; flowers 8-10 mm long, petals not unguiculate, calyx with unequal lobes, the lowest linear, narrowly triangular or subulate, 1-1.5 × 0.5 mm long; fruits oblong or falcate, 1.5-4.5 × 0.8-1.3 cm, more than 1 seed..................................................................................................................................................Dalbergia brownei

5. Leaflets 1-7, commonly attenuate or obtuse at the base; flowers 5-7 mm long, petals conspicuously unguiculate, calyx with equal or subequal lobes, 0.5 × 1.0 mm long; fruits orbicular to suborbicular or sub-square, rarely oblong, 2.2-5 × 2.1-4 cm, commonly 1 seeded...................................................................................................................................................Dalbergia monetaria

6. Flowers (9.5-) 14-20 mm long, ovary glabrous or sometimes ciliate at the margins..............................................7

6. Flowers of less of 10 mm long, ovary puberulent to variously pubescent...............................................................8

7. Calyx 7-9 mm long, hypanthium conspicuous, ribbed; inflorescences racemose; leaflets 5-7 (-9) mm long, ovate, glabrous when mature, shining, dark brown to chestnut when dry; drying fruits brown to mahogany, lustrous, never black....................................................................................................................................................Dalbergia calycina

7. Calyx 4-7 mm long, hypanthium inconspicuous, smooth or scarsely ribbed; inflorescences paniculate; leaflets 9-21 mm long, ovate, elliptic, suborbicular or oblong, densely or sparsely strigose or glabrescent when mature, opaque, dark brown to blackish when dry; drying fruits olive to dark brown or black......................................................................................................Dalbergia granadillo

8. Inflorescences congested, peduncle and rachis not visible; fruits dense and congested with peduncles less than 1.5 cm long......................................................................................................................................Dalbergia congestiflora

8. Inflorescences not congested or if congested with peduncle clearly visible; fruits not congested with peduncles of more than 2 cm long.............................................................................................................9

9. Leaflets 5; inflorescences open panicles, peduncles shorter than the inflorescences, branches of the inflorescences not thyrsoid; flowers mostly unilateral (or opening unilaterally); fruits glandular (black spots)................................................................................Dalbergia stevensonii

9. Leaflets more than 5 or at least some leaves with more than 5 leaflets; inflorescences racemes, peduncles longer than the inflorescences, branches of the inflorescences thyrsoid; flowers not unilateral (or opening in spiral); fruits eglandular...........................................................................................................................................10

10. Leaflets 5-7 (-8), some leaves with 3 leaflets...............................................................................................................................11

10. Leaflets usually 7-15 or more, some leaves with 5 leaflets ..................................................................................................................................................12

11. Leaves 9-14 cm long, leaflets 3-7; inflorescences of less than 4 cm long; ovary villose; mature fruits velutinous, ferrugineous or yellowish...............................................................................................................................Dalbergia calderonii

11. Leaves 18-23 cm long, leaflets 7 (-8); inflorescences more than 4 cm long; ovary pubescent; mature fruits strigulose or glabrescent; straw-colored or yellow...........................................................................................................................Dalbergia longepedunculata

12. Leaves less than 14 cm long, leaflets less than 1.9 cm wide; inflorescences often longer than the underlying leaves...........................................................................................................Dalbergia luteola

12. Leaves 14 cm long or at least some leaves more than 14 cm long; leaflets more than 1.9 cm wide; inflorescences always longer than the underlying leaves.......................................................................................................................13

13. Floral branchlets and underside of mature leaflets tomentose to densely tomentose, pubescence easy to feel by touch ...............................................................................................................................................................14

13. Floral branchlets and underside of mature leaflets pubescent, densely strigose, strigulose or glabrescent, pubescence difficult to detect by touch........................................................................................................................................15

14. Leaflets (10-) 11 (-12); flowers 4-4.5 mm long; stigma ciliate ....................................................................................................................................Dalbergia modesta

14. Leaflets 13-15; flowers 4.5-6 mm long; stigma glabrous.................................................................................................................Dalbergia cubilquitzensis

15. Lateral leaflets commonly more than 3 cm wide; terminal leaflet 6-8 × 3-4 cm, obovate .......................................................................................................................................Dalbergia rhachiflexa

15. Lateral leaflets commonly less than 3 cm wide; terminal leaflet 3-7 × 1.2-3 (-3.4) cm, oblong or elliptic, rarely obovate .......................................................................................................................16

16. Leaflets (15-) 19-21 ...........................................................................................................Dalbergia ruddae

16. Leaflets 9-13 ............................................................................................................................17

17. Leaflets usually oblong, membranous or chartaceous, pubescence appressed or strigose; ovary glabrous, or scarcely ciliate at the margins; fruit membranous in the wings........................................................................................................................................Dalbergia glomerata

17. Leaflets usually ovate, sometimes oblong-elliptic, chartaceous to sub-coriaceous, with sparse trichomes, crispate, or sub-appressed; ovary villous or pubescent; fruit coriaceous in the wings.............................................................................................................................................18

18. Leaflets 9-11, mostly elliptic, 2.1-5 × 1.1-2.2 cm, secondary nerves 9-12 pairs, tertiary and quaternary veins inconspicuous; inflorescences 3-4.5 cm long; mature fruits with ampulose, woody seminal chamber, with rigid wings ...................................................................................................................................Dalbergia melanocardium

18. Leaflets (11-) 13-19, mostly oblong to ovate, 4-9 × 1.8-3.5 cm, secondary nerves more than 12, tertiary and quaternary veins conspicuous, at least near the midvein; inflorescences 3.5-9 cm long; mature fruits with seminal chamber not woody nor ampulose, wings not rigid..........................................................................................................................................19

19. Leaflets usually ovate, membranous, tertiary and quarterly veins conspicuous only near the midvein, leaflets underside almost glabrous or sparsely strigulose ......................................................................................................................Dalbergia palo-escrito

19. Leaflets usually oblong or oblong-ovate, coriaceous or sub-coriaceous, tertiary and quarterly veins conspicuous along the entire lamina, leaflets underside densely pubescent with yellow or brown-yellowish trichomes...........................................................................................................................Dalbergia tucurensis

Discussion

The checklist provided here represents the baseline for any conservation efforts of the Dalbergia species in the country, according with the first target of the Global Strategy for Plant Conservation (GSPC) and the Mexican Strategy for Plant Conservation (EMCV), that calls for the “provision of a working list of known species”. Checklists facilitate the accessibility and the use of accurate botanical names, as well as information for research, conservation and sustainable use, and provide data to respond to the necessities of policy makers (^{Patton et al., 2008}), as well as enforcing authorities in the case of legally protected species, as is the case of those species within Dalbergia.

Currently, only 3 species distributed in Mexico have been assessed by the IUCN Red List: Dalbergia calycina Benth. (LC, Least concern), Dalbergia monetaria L. f. (LC, Least concern), and D. glomerata (Vu, Vulnerable), the later affected by the extraction of timber and habitat loss due to agricultural practices (^{Groom, 2012}). Moreover, only 2 species, D. congestiflora and D. granadillo, are included in the Mexican Red List (^{NOM-059-Semarnat-2010}), the only list that has legal standing in the country. Moreover, until 2016, only D. granadillo and D. stevensonii, both distributed in Mexico, were included in the appendices of the Convention on National Trade in Endangered Species of Wild Fauna and Flora data (CITES) (Table 1). Thus, this lack of information and regulation has favored in recent times the overexploitation of these very vulnerable species.

This checklist was used as the baseline to assess the risk of extinction of the timber species of Mexican Dalbergia in 2015 during a workshop organized by the National Commission for the Knowledge and Use of Biodiversity (Conabio), together with the Mexican Environmental Protection Agency (Profepa). Those species which life form are lianas were not considered in the assessment. During the workshop, a group of experts assessed the distribution, habitat, intrinsic biological vulnerability and anthropogenic impact using the Risk Evaluation Method (MER) of the Mexican Norm 059 (^{NOM-059-Semarnat-2010}), and they concluded that all Mexican native timber species of Dalbergia qualify under some risk category (Table 1). As a direct result of assessment of the Mexican timber species of Dalbergia, in 2016, the Mexican Scientific Authority of CITES submitted a proposal to list 13 timber species of Dalbergia native to Mexico under the Appendix II of CITES (D. granadillo and D. stevensonii were previously listed) (^{CITES, 2016}). This proposal was approved during the 17^th Conference of the Parties in Johannesburg in 2016 and the new CITES rosewood listings came into force on January 2, 2017 (Table 1). Thus, the 15 timber species of Dalbergia native to Mexico are now protected by this binding international Convention.

Although the species included in this checklist represent the current state of knowledge of the native species of Mexican Dalbergia, it is expected that as part of the dynamic process of taxonomy, there may be adjustments in the light of new observations and registries, as well as with the incorporation of new evidence coming from molecular studies that will help to elucidate limits among species, phylogenetic affinities, and the general patterns of diversification of the Mexican Dalbergia species.