Clock-dated phylogeny for 48% of the 700 species of Crotalaria (Fabaceae\u2013Papilionoideae) resolves sections worldwide and implies conserved flower and leaf traits throughout its pantropical range

Andréia Silva Flores,Susanne S Renner,Alexander Rockinger

doi:10.1186/s12862-017-0903-5

Abstract

BackgroundWith some 700 species, the pantropical Crotalaria is among the angiosperm’s largest genera. We sampled 48% of the species from all sections (and representatives of the 15 remaining Crotalarieae genera) for nuclear and plastid DNA markers to infer changes in climate niches, flower morphology, leaf type, and chromosome numbers.ResultsCrotalaria is monophyletic and most closely related to African Bolusia (five species) from which it diverged 23 to 30 Ma ago. Ancestral state reconstructions reveal that leaf and flower types are conserved in large clades and that leaf type is uncorrelated to climate as assessed with phylogenetically-informed analyses that related compound vs. simple leaves to the mean values of four Bioclim parameters for 183 species with good occurrence data. Most species occur in open habitats <1000 m alt., and trifoliolate leaves are the ancestral condition, from which unifoliolate and simple leaves each evolved a few times, the former predominantly in humid, the latter mainly in dry climates. Based on chromosome counts for 36% of the 338 sequenced species, most polyploids are tetraploid and belong to a neotropical clade.ConclusionsAn unexpected finding of our study is that in Crotalaria, simple leaves predominate in humid climates and compound leaves in dry climates, which points to a different adaptive value of these morphologies, regardless of whether these two leaf types evolved rarely or frequently in our focal group.

Highlights

With some 700 species, the pantropical Crotalaria is among the angiosperm’s largest genera
Closest relatives and age of Crotalaria, and flower and leaf evolution in the genus Based on our sampling of 338 (48%) of the 700 species of Crotalaria and representatives of all relevant outgroup genera, the genus is monophyletic and most closely related to the African Bolusia (5 species), followed by the monospecific likewise African Euchlora (Fig. 1)
The stem age of Crotalaria falls between the late Oligocene and the early Miocene, with the divergence from Bolusia occurring 23 (18–28, 95% credibility interval) to 30 (21–51) Ma ago (Table 1)

Summary

Introduction

With some 700 species, the pantropical Crotalaria is among the angiosperm’s largest genera. With some 700 species, Crotalaria occupies place 34 in a list of the World’s largest angiosperm genera [16]. Of these genera, only four have been studied with a species sampling >30%, namely Piper (Piperaceae) with 31% of c. The biosynthesis of pyrrolizidine alkaloids (PAs) in Crotalaria root nodules depends on infection by rhizobial bacteria [25] This has been studied in only four species of Crotalaria that turn out to be closely related (this study), and knowing the earliestdiverging species of Crotalaria, as well as the closest relatives of the genus, is required to infer when this trait may have evolved

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