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

Open Access
Publisher Website
Google Scholar
Abstract
In this survey of floral structure, the number of Ludwigia spp. prepared anatomically was increased to 37. Mectaries of diplostemonous ludwigias are trichome-covered depressions in the (often raised) summit of the ovary, whereas nectaries of sects. Dantia, Microcarpium and Miquelia are convex and hairless. Nectaries of sect. Ludwigia though hairless, are otherwise closer to those of the diplostemonous ludwigias. Vascular features are not useful for grouping Ludwigia spp. For example: the degree to which petal midveins extend basally differs markedly from species to species, some midveins ending in the vascular girdle, others passing through the girdle to the flower''s base. But species that are alike for this trait are too unlike in others ways to be allied. The level at which the major bundles of a Ludwigia flower part is not a trustworthy indicator of evolutionary level: in some species, at least, it has more to do with the shape of the flower than with gradual phyletic union of appendages. In some ludwigias large bundles in the locular radii retard dehiscence and ensure slow dispersal of seeds. Onagraceous styles commonly carry 1 bundle in each locular radius and no others, but some of the ludwigias have a 2nd set in the septal radii at the style''s base, apparently an archaic trait. Ludwigia is the only onagraceous genus in which ovules are supplied by central as well as by transseptal bundles, a peculiarity linked functionally with deeply intrusive placentas and maybe with pollen tetrads. To account for this dual supply.sbd.at the same time for Ludwigia''s oddly placed nectaries and lack of a floral tube.sbd.it was argued that epigyny evolved twice in the family, once in the line leading to Ludwigia and once in the line leading to all other onagrads.