Ludwigia sect. Ludwigia
Onagraceae subfam. ludwigioideae
erect, subterete to angled.
alternate.
stipules present.
4-merous;
petals present, yellow;
stamens as many as sepals;
pollen usually shed in tetrads.
floral tube absent;
sepals (3 or)4 or 5(–7), persistent at ovary apex after dehiscence of other floral parts;
petals yellow or white, rarely absent.
globose to cuboid, 4-angled or terete, with hard walls, dehiscent by an apical pore.
in several rows per locule, free, raphe an inconspicuous, longitudinal ridge.
= 16.
Ludwigia sect. Ludwigia
Onagraceae subfam. ludwigioideae
Species 4 (4 in the flora).
Species of sect. Ludwigia are found mainly along the coastal plain of southeastern United States.
Section Ludwigia consists of four perennial diploid species native to the southeastern United States; L. hirtella extends north to Rhode Island and L. alternifolia to Ontario and into the Great Plains of central North America (P. A. Munz 1965). Ludwigia virgata is outcrossing, the other three are autogamous. This strongly supported monophyletic section (P. H. Raven 1963[1964]; Liu S. H. et al. 2017) differs from the other sections found in North America by having fusiform, tuberous roots that may have an adaptive function in wet habitats, and capsules regularly dehiscing by an apical pore. The free seeds are loose in the globose capsules until they dehisce through the pore, giving rise to the common names seedbox or rattlebox. All species of sect. Ludwigia consistently shed their pollen in tetrads; J. Praglowski et al. (1983) reported for all taxa in this section that sometimes the tetrads appeared to be linked, suggesting polyads.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genus 1, species 82 (31 in the flora): North America, Mexico, West Indies, Bermuda, Central America, South America, se Asia, Africa, Indian Ocean Islands, Pacific Islands, Australasia; introduced in Europe, w Asia.
Ludwigioideae were segregated as a distinct subfamily (W. L. Wagner et al. 2007) to reflect the phylogenetic relationship of Ludwigia as sister to other genera of Onagraceae in morphological and molecular analyses (see R. A. Levin et al. 2003, 2004). Ludwigia is distinguished by the absence of a floral tube, persistence of sepals on capsules after other floral parts dehisce, pollen shed in tetrads or polyads (or as monads in some sections, tetrads sometimes found elsewhere in Onagraceae), double ovule vascular supply, uniquely including a central supply (R. H. Eyde 1981), single-celled ovule archesporium (H. Tobe and P. H. Raven 1996), and a base chromosome number of x = 8.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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