Large flower primrose willow

Emergent Plants

Ludwigia uruguayensis:

Large flower primrose willow

Ludwigia uruguayensis (Camb.) Hara (formerly Ludwigia hexapetala, Ludwigia grandiflora): Large flower primrose willow; water primrose. Onagraceae (evening-primrose family). 

Native perennial. A shoreline and water margin plant that forms dense mats, rooting from leaf nodes into moist soil or water and growing up to 3 ft (90 cm) in height. When overwintering and before flowering the plant has a compact rosette form, with shiny, mostly smooth, bright green leaves on very short stems. These rosette leaves are rounded ovals with well-marked mid- and side veins. As plants approach flowering, the stems lengthen, become more hairy, and produce leaves of another type; these are alternate on the stem, very narrow, pointed, and up to 4.75 in (12 cm) long. The showy flowers, 1.5 in (3.75 cm) wide, are borne singly, having usually 5 (sometimes 6) bright yellow petals; their stalks and sepals are hairy. The fruit is a 5- to 6-ridged cylinder and has numerous cube-shaped seeds. Considered a nuisance species in many areas, water primrose's aggressive dense growth clogs waterways and interferes with shoreline activities.