Ludwigia palustris (L.) Ell.
Family - Onagraceae
Stems - To 50 cm, usually prostrate and creeping, branched and mat-forming, sometimes with ascending tips, rooting at nodes, not spongy, glabrous.
Ascending stem tips
Stem and nodal roots.
Leaves - Opposite, petiolate. Blades to 4.5 cm, narrowly to broadly elliptic, tapered at base, margins entire but short-hairy, glabrous. Venation pinnate, with lateral veins distally fused to marginal vein. Stipules present but minute.
Flowers - Axillary, sessile or nearly so, bractlets present but minute. Sepals 4, to 2.0 mm long, green, broadly lanceolate to broadly ovate-triangular, sharply pointed at the tip. Petals absent. Stamens 4, the filaments green, somewhat translucent. Pistil 1, with 4-locular inferior ovary. Stigma capitate.
Flowering - May - September.
Habitat - Shallow water, muddy pond margins, slow streams, ditches, swamps, spring branches.
Origin - Native to U.S.
Other info. - This species can be found throughout much of Missouri but is absent from most of the
northern 1/4 of the state. The plant can be identified by its wet habitat, opposite stems, and tiny greenish flowers.
The absence of petals render it relatively inconspicuous.
Photographs taken near Angel Mounds, Evansville, IN., 8-5-06 (DETenaglia); also at Cuivre River State Park, Lincoln County, MO, 8-10-2015 (SRTurner).