Ludwigia leptocarpa (Nutt.) H. Hara
Hairy Primrose Willow
Family - Onagraceae
Stem - Stems erect or ascending, to 2.5 m, terete, longitudinally lined, densely pubescent with spreading hairs.
Stem and node.
Stem and fruit.
Leaves - Leaves alternate, petiolate. Leaf blades to 18 cm, lanceolate to oblanceolate, the margins entire, the surfaces moderately to densely hairy when young, at maturity the pubescence mostly restricted to the main veins, the relatively inconspicuous venation pinnate, but with the secondary veins fused to form a series of submarginal loops. Stipules present, to 0.5 mm.
Stem and leaves.
Flowers - Axillary, on short stalks, bractlets usually absent. Sepals 5, to 11.0 mm long, lanceolate, tapered to a sharply pointed tip. Petals usually 5, 5-11 mm long, 4-8 mm wide, broadly obovate, broadly rounded or with a shallow notch at the tip, yellow to orangish yellow. Stamens usually 10, the filaments yellow. Pistil 1, with 5-locular inferior ovary.
Fruits - Capsules to 4.5 cm, more or less cylindric, rounded or slightly several-angled, straight or slightly curved, thin-walled, hairy, dehiscing tardily and irregularly. Seeds 1.0-1.2 mm long, loosely embedded in horseshoe-shaped pieces of inner fruit tissue, the surface pale brown, finely pitted, shiny.
Fruit cross section
Flowering - August - October.
Habitat - Riverbanks, margins of ponds and sloughs.
Origin - Native to the U.S.
Other info. - This species is uncommon in Missouri, with a range mostly restricted to the Mississippi Lowlands Division. More recently, the plant has also been found in a few locations within St. Louis County. The long fruits in combination with the showy yellow flowers make it a species hard to miss and easy to identify. The number of flower petals is usually 5, with twice that many stamens; however, 6-petaled flowers are not uncommon. The species epithet 'leptocarpa' means 'slender fruits.'
Photographs taken at Creve Coeur Lake Memorial Park, St. Louis County, MO 9-30-2015, and at Duck Creek Conservation Area, Stoddard County, MO, 10-18-2017 (SRTurner).