Reproductive Structures and Evolution in Ludwigia (Onagraceae). III. Vasculature, Nectaries, Conclusions

To complete this iid of floral structure the number of Ludwigia species prepared anatomically-cleared, sectioned, oth-was increased to 37. In general, nectaries of diplostemonous ludwigias are trichome-eed den in the Ads raised) summit of the ovary, whereas nectaries of sects.Dantia, Microcarpium, an iquelia are convex and hairless.Nectaries of sect.Ludwigia, though hairless, are otherwise closer to those of the diplostemonous ludwigias.Vascular o are too unlike in others ways to be allied.The level at d the major bundles of a Ludwigia flower part is not a trustworthy puri of evolutionary level: ome species, at least, it has more to do with the shape of the flower than with Vias m union 1 of appendages.In some ludwigias large bundles in the locular radii retard dehiscence and ensure slow dispersal of seeds.Onagraceous styles commonly carry one ndle in each Jocular radius ond no others, but some of the ludwigias have a wi id in sit sepia "radii at the style's base, apparently an archaic trait.Ludwigia is the only whic ovules are supplie y central as well as by transseptal bundles, a pee ana linked Piika em with deeply intrusive placentas and maybe with pollen tetrads.To account for this dual supply-at the same time for Ludwigia's oddly placed nectaries and lack of a floral tube-I argue that epigyny evolved twice in the family, once in the line leading to Ludwigia and once in the line leading to all other onagrads.Gynoecial nectaries and a central ovular supply are among the traits that set Ludwigia apart from other onagraceous genera.Throughout the family vascular bundles supplying the ovules pass transversely through the septa of the inferior ovary.Ludwigia species commonly have additional bundles running up the center of the ovary.The central system is reported here for the first time along with other aspects of floral vasculature deemed to have systematic worth.I shall argue !I thank Peng Ching-I, T. P. Ramamoorthy, and P. H. Raven for