Ludwigia spathulata
Onagraceae subfam. ludwigioideae
southern water purslane, spoon primrose-willow
prostrate or decumbent and ascending distally, slightly ridged, well branched, 10–40cm, densely strigillose throughout.
opposite;
stipules narrowly deltate or ovate, 0.05–0.15 × 0.05–0.1 mm;
petiole very narrowly winged, 0.3–0.9 cm, blade elliptic-spatulate or narrowly so, 0.9–1.7 × 0.3–0.9 cm, base attenuate, margins entire, apex acute, surfaces strigillose;
bracts not reduced except at branch tips.
stipules present.
leafy spikes or racemes, flowers usually paired in leaf axils;
bracteoles attached at base of ovary or on short pedicel, narrowly oblong or oblanceolate, 0.2–0.8 × 0.05–0.2 mm, apex acute, often obscured by hairs.
sepals ascending, pale green, broadly ovate-deltate, 1–1.7 × 1.1–1.7 mm, margins entire, apex acuminate, surfaces densely strigillose;
petals 0;
filaments translucent, 0.5–0.8 mm, anthers 0.2–0.4 × 0.3–0.5 mm;
pollen shed singly;
ovary oblong-obovoid, 4-angled to subterete, 1.5–2.5 × 1–1.5 mm;
nectary disc elevated 0.1–0.2 mm on ovary apex, yellowish green, 0.7–0.9 mm diam., 4-lobed, glabrous;
style yellowish green, 0.3–0.5 mm, glabrous, stigma pale yellow, capitate, 0.2–0.3 × 0.2–0.3 mm, not exserted beyond anthers.
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.
oblong-obovoid, subterete, 2.5–4(–4.5) × 1.5–2.5 mm, thin-walled, seeds often visible on exocarp as small bumps, irregularly dehiscent or dispersing as unit, pedicel 0–0.5 mm.
dark reddish brown, ellipsoid, 0.5–0.7 × 0.4–0.5 mm, surface cells transversely elongate.
= 32.
Ludwigia spathulata
Onagraceae subfam. ludwigioideae
Flowers May–Sep. Ditches, swales, edges of ponds, lakes, sinks, swamps, sandy river bars, dried seasonal ponds, disturbed low savannas; of conservation concern; 0–200 m; Ala., Fla., Ga., S.C.
The tetraploid Ludwigia spathulata is relatively uncommon and occurs primarily on the Gulf Coastal Plain in the panhandle of Florida, southern Alabama, and southwestern Georgia. Outlying populations have also been collected in transitional areas between the Coastal Plain and the Piedmont in South Carolina and Georgia. With its small apetalous flowers, L. spathulata is modally autogamous and shows low morphological variability. Its strongest affinities appear to be with L. palustris, with which it shares a genome (C. I. Peng 1988, 1989).
(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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