Observations on the Ludwigia uruguayensis Complex (Onagraceae) in the United States

ABSTRACT
Ludwigia uruguayensis is known to comprise a decaploid entity (L. hexapetala) and a hexaploid one (L. grandiflora, including the type of L. uruguayensis), but the two chromosomal races differ only by quantitative, intergrading morphological features, a large portion of their genome is hypothesized to be shared, and they are known to produce hybrids of intermediate morphology in regions of sympatry. Ludwigia hexapetala is the more common, but both occur in the southeastern United States. We agree in general with earlier studies regarding the nature of the distinction between the two entities but suggest that a more reasonable treatment of them would be as subspecies within a single species: L. grandiflora subsp. grandiflora and L. grandiflora subsp. hexapetala, comb. et stat. nov.