Subfamily Caesalpinioideae is a paraphyletic grade of 171 genera that comprises the first branches of the Leguminosae and from which are derived the monophyletic subfamilies Mimosoideae and Papilionoideae. We have sequenced the chloroplast matK gene, and the trnL and 3′-trnK introns for 153 genera of caesalpinioid legumes. Parsimony and Bayesian phylogenetic analyses of these data support the monophyly of several major groups within the caesalpinioid legumes: the Cercideae, Detarieae, Detarieae s. str., Prioria , Amherstieae, Dialiinae, Cassia , Caesalpinia , Peltophorum , and Tachigali clades. Relationships among the first branching lineages of the legumes are not well supported, with Cercideae, Detarieae, and the genus Duparquetia alternatively resolved as sister group to all of the legumes. The division of certain large genera (e.g., Caesalpinia s. l., Bauhinia s. l.) into segregate genera generally is supported by our molecular data. Using 18 well-documented fossils as calibration points, fixing the stem node of the legumes at 65 Ma, and using the Penalised Likelihood method, we estimate the crown node of the Leguminosae at 64 Ma and the crown age of each of the major caesalpinioid lineages varying from 34 to 56 Ma. Fossil cross-validation suggests that none of the 18 fossil calibrations is internally inconsistent. Analyses done without fossil calibrations yield much younger divergence times. The age estimates for the Detarieae clade are more sensitive to the presence of calibration points than other caesalpinioid clades, a situation which we attribute to the slow rate of chloroplast DNA evolution in this group.

Rosa rugosa, a vigorous ornamental shrub introduced from Asia in the 19th century, is now naturalized in coastal northeastern North America, where it occasionally grows in sympatry with the native R. blanda. To document hybridization between these species, evaluate its extent across the area of sympatry, and examine the use of morphology as a field monitoring tool, we sampled 179 individuals of parental species and putative hybrids in 13 pure and 11 mixed populations. We developed allele-specific primers to assay single nucleotide polymorphisms (SNPs) markers from one chloroplast region and four low-copy nuclear introns. Our results revealed frequent bidirectional hybridization and infrequent introgression in sympatric populations of these species. The recurrent presence of F(1) hybrids in mixed populations indicated the weakness of early-acting reproductive barriers. Morphological data were concordant with molecular data and provided additional evidence for the presence of a few backcrosses. Morphological analyses yielded diagnostic characters for identifying hybrids and monitoring the hybrid zone. Such hybridization could ultimately lead to the genetic assimilation of R. blanda in mixed populations and to the formation of invasive hybrid genotypes, a phenomenon that is of economic and ecological concern because of the increasing number of exotic species worldwide.