Ludwigia alternifolia L.
CC = 4
CW = -5
MOC = 70
Family - Onagraceae
Habit - Perennial forb with fleshy, somewhat thickened roots.
Stems - Strongly ascending to erect, to 1.5 m, angled (angles minutely winged), single or multiple from base, unbranched to much-branched toward the tip, the bark splitting near the base in older plants, glabrous or pubescent with short hairs in lines decurrent from the leaf bases.
Leaves - Alternate, simple, sessile to short-petiolate. Petioles 1-3 mm long. Stipules 0.2-0.3 mm long, ovate-triangular to peg-like, dark reddish purple, succulent. Leaf blades 2.0-12.0 cm long, 10-12 mm wide, lanceolate to narrowly lanceolate or lanceolate-elliptic, tapered at the base, angled to a sharply pointed tip, the margins entire but antrorse strigillose, the surfaces variably short-hairy, especially along the veins, the venation pinnate, but the secondary veins more or less fused to form a submarginal vein or loops.
Inflorescence - Single axillary flowers from upper leaves. Pedicles 4-angled, antrorse pubescent, 2-7 mm long at flowering and fruiting, the bractlets narrowly lanceolate, green, short-hairy.
Flowers - Sepals 4, 6.5-9.6 mm long, 4.0-6.8 mm wide, green or reddish-tinged, ovate-triangular, bluntly or sharply pointed at the tip. Petals 4, 10-14 mm long, 8-12 mm wide, obovate to obtriangular or nearly orbicular, broadly rounded to truncate or with a shallow notch at the tip, yellow. Stamens 4, the filaments white, 1.0-3.0 mm long; the anthers 1.0-1.7 mm long. Style green, 2-3 mm long, glabrous. Stigma green, capitate. Ovary inferior, 4-locular. Placentation axile. Nectaries between sepals (at base of stamens) to 0.5 mm long.
Fruits - Capsules 4-7 mm long, 4-6 mm wide, subglobose to nearly cubic, 4-angled and often narrowly 4-winged, hard-walled, glabrous or short-hairy, dehiscing by a terminal pore (sometimes eventually breaking into 4 valves with age). Seeds 0.5-0.8 mm long, oblong-cylindric, sometimes slightly curved, free from the fruit tissue at maturity, the surface yellowish brown, shiny, with a fine network of ridges.
Flowering - June - August.
Habitat - Streambanks, pond margins, marshes, fens, seeps, bottomland prairies, swamps, ditches, railroads, and roadsides.
Origin - Native to the U.S.
Lookalikes - Other species of Ludwigia.
Other info. - This species can be found throughout most of Missouri, except for the northwest corner of the state. Beyond Missouri it ranges throughout most of the eastern half of the continental U.S. The flowers resemble those of several other species of Ludwigia However, this plant is larger than the others, and the hypanthium and fruits have a distinctively boxlike shape (hence the name "seedbox"). The flowers are fairly showy and larger than other Missouri species of the genus. Plants growing in optimal conditions can be quite striking. The flowers petals of this and other species of Ludwigia fall off very easily if the plant is shaken or disturbed. Preparing a pressed specimen with nicely intact flowers is challenging.
Photographs taken at the Peck Ranch Wildlife Refuge, Shannon County, MO., 7-12-03 (DETenaglia); also at Otter Slough Conservation Area, Stoddard County, MO, 7-18-2009, Route 66 State Park, St. Louis County, MO, 8-29-2009, Weldon Spring Conservation Area, St. Charles County, MO, 8-14-2014, and Holly Ridge Conservation Area, Stoddard County, MO, 7-31-2015 (SRTurner).