Ludwigia alternifolia L.

Ludwigia alternifolia plant

Family - Onagraceae

Stems - To 1m tall, branching, erect, herbaceous, angled (angles minutely winged), antrorse pubescent, single or multiple from base, from thickened roots.

Ludwigia alternifolia stem

Leaves - Alternate, sessile to short-petiolate, lanceolate to lance-elliptic, acute, tapering at base, sparse pubescent, entire, to +12cm long, 2cm broad. Margins antrorse strigillose. Lateral veins from midrib converging with longitudinal veins before margin.

Ludwigia alternifolia leaves

Inflorescence - Single axillary flowers from upper leaves. Pedicles to 5mm long in flower, longer in fruit, 4-angled, antrorse pubescent, with 2 subopposite bracts. Bracts to 3mm long.

Flowers - Petals 4, yellow, free, 5-7mm long and broad, emarginate to rounded at apex, glabrous. Stamens 4, alternating with petals. Filaments brownish-yellow, glabrous, 1.5mm long. Anthers 2.2.5mm long, yellow. Style green, 2-3mm long, glabrous. Stigma green, capitate. Ovary inferior, 4-locular. Placentation axile. Floral tube 4-angled, 4mm long and broad, winged on angles, appressed pubescent. Wings 1.5mm broad, antrorse pubescent on margins. Sepals 4, -1cm long, 6mm broad (slightly larger in flower), ovate, acute, glabrous, ciliate-margined. Nectaries between sepals (at base of stamens) to .5mm long.

Ludwigia alternifolia calyxFloral tube and sepals.

Ludwigia alternifolia flower

Flowering - June - August.

Habitat - Wet ground, borders of stream and bodies of water.

Origin - Native to U.S.

Other info. - This species can be found scattered throughout the state of Missouri. The flowers are fairly showy and larger than in any other Missouri species from the genus. The species name comes from the fact that the leaves are alternate but there are also 3 other species found in the state which have alternate leaves. The flowers petals fall off very easily if the plant is shaken or disturbed. I was taught to use this characteristic as a field identification trick for the Onagraceae in college.
The plant varies in the amount of pubescence on the stems and leaves. Some plants can be completely glabrous.

Photographs taken at the Peck Ranch Wildlife Refuge, Shannon County, MO., 7-12-03.