Insights into Species Delimitation of Selected Species in the Flowering Plant GenusMedicagosectionBuceras(Leguminosae)

Abstract

Abstract—The genusMedicago(Leguminosae, Papilionoideae) contains about 90 species including the important forage crop alfalfaMedicago sativaand the genomic modelMedicago truncatula. Despite intensive research on the genus because of its agricultural importance, there is a relative lack of information about chromosome number and genome size in someMedicagospecies, especially those fromMedicagosectionBucerasthat were formerly placed in the sister genusTrigonella, and are paraphyletic to the remainder of the genusMedicago. Past studies revealed that previous species delimitations did not conform well with complex patterns of morphological or genetic variation. Some published chromosome numbers, e.g. 2n =28 and 2n= 44, differ from those of the rest of the genus, which are mostly 2n= 16 or polyploids thereof, although some cases of aneuploid reduction or dysploidy (e.g. 2n =14) do exist. Here we estimated phylogenetic relationships of 42 accessions corresponding to 14 currently recognizedMedicagospecies that are paraphyletic to the remainder ofMedicagowith a focus onMedicago monantha; for a number of those accessions we obtained estimates of genome size (39) and chromosome number (14). We can confirm the delimitation of two species withinM. sectionBucerasand our data suggest that there are at least two entities with distinct geographic distributions within the currently recognized speciesM.monantha, which differ in chromosome number and genome size. Our data also suggest that polyploidy and post-polyploid descending dysploidy played a significant role in genome evolution withinM. sectionBuceras. Our data provide a strong foundation for whole-genome sequencing projects and further in-depth research of these paraphyletic lineages.