Spoon primrose-willow, southern water purslane

Isnardia spathulata (Torrey &A. Gray) Kuntze

Herbs creeping and rooting at nodes, often forming mats. Stems prostrate or decumbent and ascending distally, slightly ridged, well branched, 10–40 cm, densely strigillose through­out. Leaves 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. Inflorescences 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. Flowers: 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. Capsules 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. Seeds dark reddish brown, ellipsoid, 0.5–0.7 × 0.4–0.5 mm, surface cells transversely elongate. 2n = 32.

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).