An update of the Verbenaceae genera and species numbers

1Universidade Federal do Rio de Janeiro, Museu Nacional, Departamento de Botânica, Quinta da Boa Vista, CEP 20940-040, Rio de Janeiro, RJ, Brazil 2Instituto de Botánica Darwinion (ANCEFN-CONICET), Labardén 200, CC 22, B1642HYD, San Isidro, Buenos Aires, Argentina 3Department of Biology and Burke Museum, University of Washington, Seattle, WA 98195 USA 4Universidade Federal do Rio Grande do Sul, Departamento de Botânica, Programa de Pós-Graduação em Botânica, CEP 91501-970, Porto Alegre, RS, Brazil *Corresponding author: veronicathode@hotmail.com RESEARCH ARTICLE


INTRODUCTION
Tropical regions of the Americas are some of the most species-rich ecoregions in the world and several studies have investigated its plant diversity (Antonelli & Sanmartín 2011;Ulloa et al. 2017). Yet, some lineages are challenging and still need further investigation, such as the taxonomically complex and diverse family Verbenaceae. This group is a particularly important component of arid to semi-arid communities in the New World (Frost et al. 2017), but is also well represented in wet and dry tropical forests, high Andean grasslands, and cloud forests (Olmstead 2013).
First described by Saint-Hilaire (1805), the vervain family has been variously circumscribed (e.g. Schauer 1847;Briquet 1895;Troncoso 1974;Atkins 2004). The composition and close allies of Verbenaceae have been controversial, and relationships among genera ascribed to the family have been poorly understood. In this context, much of that diversity was recognized to be more closely related to Lamiaceae by Junell (1934). Later, this was confirmed by phylogenetic studies (Cantino 1992;Wagstaff & Olmstead 1997), with 10 tribes and about 50 genera previously belonging to the Verbenaceae being transferred to the Lamiaceae (Cantino et al. 1992).
One of the most active researchers on Verbenaceae was Harold N. Moldenke, who described several genera and hundreds of species and infraspecific taxa within the family. These descriptions are dispersed in numerous publications between 1930 and 1980. Nélida Troncoso also made important contributions to the taxonomy of the family (Troncoso 1974). Atkins (2004) presented a historical overview on the classification of Verbenaceae, including a compilation of several studies based on different sources of evidence, such as morphology, anatomy, inflorescence structure, palynology, and karyology. In this treatment, 34 genera and around 1200 species were estimated for the family, organized into six tribes (Atkins 2004).
With the widespread adoption of DNA sequencing, molecular systematics began to revolutionize the understanding of relationships within Verbenaceae. The most comprehensive molecular phylogeny for the family to date was proposed by Marx et al. (2010), who recognized eight tribes (Casselieae, Citharexyleae, Duranteae, Lantaneae, Neospartoneae, Petreeae, Priveae, Verbeneae) and 35 genera. A subsequent study (O'Leary et al. 2012a) found morphological traits that support most of the tribes of Marx et al. (2010). The classification proposed by Marx et al. (2010) has formed the basis for the regional treatment of the family as a whole for floristic and systematic projects, including the Flora Argentina ) and Flora of Brazil (2020).
Since the work of Marx et al. (2010), many publications based on morphology and/or molecular data have proposed important changes within the family, including several generic realignments. In tribe Duranteae, Verbenoxylum has been included within Recordia (Thode et al. 2013); in tribe Citharexyleae, Baillonia has been included within Citharexylum (Christenhusz et al. 2018); in tribe Lantaneae Acantholippia and Xeroaloysia were included in Aloysia (Lu-Irving et al. 2014); while Diphyllocalyx and Isidroa were described as new genera (Greuter & Rodríguez 2016), and in tribe Petreae, Xolocotzia has been included within Petrea (Christenhusz et al. 2018). The inclusion of Diostea in Dipyrena by Ravenna (2008) is contradicted by phylogenetic evidence and has not been accepted. Diostea belongs to tribe Neospartoneae, while Dipyrena remains unassigned to a tribe (Marx et al. 2010).
Numerous nomenclatural changes have occurred in the tribe Verbeneae since Atkins (2004) and before Marx et al. (2010), including recognition of the genus Mulguraea (e.g. O'Leary et al. 2007O'Leary et al. , 2009). In addition, Frost et al. (2017), while investigating the role of a putative Andean dispersal corridor connecting North and South America in Verbeneae, identified a distinct and as yet unnamed clade in this tribe comprising species currently assigned to Junellia and Verbena. Later, after Marx et al. (2010), substantial changes were proposed within tribe Lantaneae, which has been the subject of several phylogenetic studies and taxonomic revisions (O'Leary & Múlgura 2012; Lu-Irving & Olmstead 2013;Lu-Irving et al. 2014, in press;Greuter & Rodríguez 2016). These studies suggest the need for redefining the generic boundaries within Lantaneae. As mentioned above, Aloysia and related genera have already been recircumscribed (Lu-Irving et al. 2014;, with Aloysia now including taxa previously recognized as Acantholippia and Xeroaloysia. The remainder of Lantaneae forms a large clade comprising seven genera in which five from among them are embedded within the two large genera, Lantana and Lippia, neither of which is monophyletic (Lu-Irving et al. in press).
These results also show that the African/Malagasy genus, Coelocarpum, which was assigned to Lantaneae by Marx et al. (2010), despite being morphologically discordant, is sister to all other Lantaneae, raising the question whether to include it in the tribe at all (Lu-Irving et al. in press).
In light of above, the need for a review of the estimates of genus and species numbers in the Verbenaceae becomes evident. Thus, based on a compilation of the past 16 years of taxonomic and phylogenetic studies on the family, we here provide a list of the currently accepted Verbenaceae genera with the number of species they include compared to the numbers reported by Atkins (2004) and with an indication of the tribe to which they are assigned sensu Marx et al. (2010). In addition, information about their geographical distribution is also provided, along with references to most recent monographic or other systematic study carried out for each genus.

RESULTS
Our compilation shows that Verbenaceae has 32 genera and 800 species currently recognized (  Cardoso et al. 2019aCardoso et al. , 2019bCardoso et al. , 2019cCardoso et al. , 2019dCardoso et al. , 2019e, 2019f, 2019g, 2020Harley et al. 2019;Moroni et al. 2019;Thode & Bordignon 2019), this estimate of the number of species is a reduction of approximately onethird from that of Atkins (2004), which continues to be used to represent the diversity in Verbenaceae due to the lack of an updated estimate for the species number in this family. Since the publication of Marx et al. (2010), five genera were placed in synonymy, while two others were described (see above and table 1). Although ongoing work on tribe Lantaneae is likely to change the number of genera recognized in that tribe in the future, the update for the family proposed here is important for current taxonomic and floristic projects involving Verbenaceae. Finally, this compilation is a first step for continuing updates, as new taxonomic changes within the family are necessary.
Ongoing research on the taxonomy and phylogeny of specific groups within Verbenaceae is active (e.g.   Marx et al. (2010). The last comprehensive species estimates by Atkins (2004) are updated based on the most recent monographs and other systematic studies. 1 synonym under Citharexylum; 2 synonym under Recordia; 3 synonym under Aloysia; 4 genera described after Marx et al. (2010); 5 synonym under Petrea; 6 synonym under Junellia; * genera for which circumscription is likely to change based on Lu-Irving et al. (in press Moldenke (1937)