DOI: 10.5061/dryad.crjdfn35r
title: Systematics of Vigna subgenus Lasiospron (Benth.) Maréchal et al. (Leguminosae: Papilionoideae: Phaseolinae)

description: A taxonomic treatment is herein provided for the six primarily Neotropical
 species of Vigna subg. Lasiospron. This subgenus is distinguished, in
 part, by its close relationship with Old World Vigna species, but rather
 than having an Old World Vigna floral asymmetry where distal floral parts
 can have a right-hand curvature (from a face-view perspective), distal
 parts of subg. Lasiospron flowers, like those of American Phaseolinae,
 curve to the left. Our proposed taxonomy reflects published phylogenetic
 analyses that resolve the subg. Lasiospron species in a subclade of the
 primarily Old World clade of species of Vigna sensu stricto. Vigna subg.
 Lasiospron is therefore distinctive in having a primarily neotropical
 distribution. Three of the six subg. Lasiospron species have an
 amphi-Atlantic distribution, which we suggest was achieved naturally be
 the ability of these species to disperse and colonize coastal habitats.
 Nomenclatural and taxonomic synonyms are reported, along with species
 descriptions and the biogeographical, genetic, and morphological evidence
 that argues for each of the six Lasiospron species fitting a unified
 species concept.
description: We reanalyzed 160 ITS accessions
 representing the 67 species of the <i>Vigna</i> sensu lato
 clade resolved by Delgado-Salinas et al. (2011). This clade comprises the
 African genus <i>Physostigma</i> and the mostly African and
 Asian species of <i>Vigna</i> sensu stricto. The latter
 includes the focal subclade of this analysis, <i>Vigna</i>
 subg. <i>Lasiospron</i>, the American
 <i>Vigna</i>. The <i>Vigna</i> sensu stricto clade
 and <i>Physostigma</i> from the sister clade to the American
 Phaseolinae (<i>Ancistrotropis</i>,
 <i>Cochliosanthus</i>, <i>Condylostylis</i>,
 <i>Dolichopsis</i>, <i>Helicotropis</i>,
 <i>Leptospron</i>, <i>Macroptilium</i>,
 <i>Mysanthus</i>, <i>Phaseolus</i>,
 <i>Oxyrhynchus</i>, <i>Ramirezella</i>,
 <i>Sigmoidotropis</i>, and <i>Strophostyles</i>;
 Delgado-Salinas et al. 2011). We included conspecific samples of species
 from these genera to test the delimitation of species of
 <i>Vigna</i> subg. <i>Lasiospron</i> and compare
 patterns of coalescing conspecific genetic samples within subg.
 <i>Lasiospron</i> with such patterns in other subclades of
 <i>Vigna</i> sensu lato. <b><i>Phylogenetic
 Analysis</i></b>—We conducted a Bayesian phylogenetic analysis
 of an ITS sequence data set from Delgado-Salinas et al. (2011) using BEAST
 2.6.2 (Bouckaert et al. 2019). We did not redo the analysis of the
 chloroplast locus <i>trnK</i>/<i>matK</i> because
 those data do not included multiple conspecific accessions of subg.
 <i>Lasiospron</i> species (Delgado-Salinas et al. 2011) and
 because such studies as Raveenadar et al. (2018) find ITS sequence data to
 be significantly more informative at the species level in the genus
 <i>Vigna</i> than any of the commonly used cpDNA loci. The
 Bayesian analysis included partitioning the ITS region into three
 subregions (i.e., the internal transcribed spacer 1, the 5.8S locus, and
 the internal transcribed spacer). The nucleotide substitution model
 involved model averaging using bModelTest (Bouckaert and Drummond 2017) or
 using the general time reversible nucleotide substitution model, as in
 Delgado-Salinas et al. (2011). Multiple MCMC chains each included
 100 M generations sampled every 90 K generations such that a 10% burnin
 yielded 1000 sample points at likelihood stationarity. Using Tracer
 (Rambaut et al. 2018), we inspected likelihood scores simultaneously from
 multiple Bayesian runs, which invoked the same or differing combinations
 of settings (e.g., one versus three ITS data partitions, bModelTest versus
 general time reversible site models, and birth-death versus Yule tree
 models). In this manner we verified that all Bayesian runs achieved
 likelihood stationarity and determined the effect on the results of
 invoking different combinations of site and tree
 models. The main tree prior included the
 root of <i>Vigna</i> sensu lato (the entire data set) with an
 age constraint set as a normally distributed density calibration of 8.0 ±
 0.8 Ma (Lavin et al. 2005) rather than 9.1 Ma ± 1.0 (Delgado et al. 2011).
 This is because we wanted to bias ages toward conservative (minimum)
 estimates. With the root age so constrained, we made age estimates for the
 stem clades of <i>Vigna</i> sensu stricto plus
 <i>Physostigma</i>, the American Phaseolinae, all genera of
 the American Phaseolinae, and all the main subclades of
 <i>Vigna</i> sensu stricto including subg.
 <i>Lasiospron</i>.
description: The file is in Nexus format.