Habit: Perennial, floating and emergent, herbaceous forb

Stem/roots: non-flowering, sprawling stems float along the water surface with roots at the stem nodes; upright stems freely branching and flowering; pubescent

Leaves: alternating leaves on floating stems are spatulate (spoon-shaped), petiolate (leaf stems), and have rounded apices; alternating leaves on upright stems are lanceolate (lance-shaped), mostly sessile, and have acute apices; pubescent

Flowers: solitary flowers at leaf axils of upright stems; pedicels 1-5 cm, usually confused with floral tubes; a pair of small bractlets indicate the separation of the pedicel and floral tube; pedicel and floral tube pubescent; calyx of 5, sometimes 6, acute sepals, 10-12 mm, pubescent on the outside; corolla of 5, sometimes 6, bright yellow, rounded petals, 1-2 cm long and wide; stamens 8-12, twice the amount of sepals/petals

Fruits: fruit a pubescent, cylindric capsule 1-2.5 cm long, 3-4 mm wide

Look-alikes: Many Ludwigia species have similar leaves and flowers, but those two organs are key to determining identity. The alternate leave arrangement, the 8-12 stamens, and the 5-6 petals differentiate to about four species. The Ludwigia uruguayensis species complex includes L. grandiflora and L. hexapetala. Leaves on upright stems will be mostly lanceolate (widest portion of the leaf in the leaf center) on L. grandiflora and mostly oblanceolate (widest portion of the leaf in the top half of the leaf) on L. hexapetala, and stem nodes are swollen along the lower portion of upright stems on L. hexapetala (Colette Jacono, Univ. of Florida, pers. comm. 2017). Upright stems of L. hexapetala have pubescent stems, leaves, and floral tubes, distinguishing them from L. peploides, which are mostly glabrous (hairless) and lack upright stems. Floral tubes/capsules of L. hexapetala are narrower and longer than those of L. peruviana, which have stout and pyramidal floral tubes/capsules. The native L. leptocarpa has smaller petals (<1 cm) than those of L. hexapetala (>1 cm), usually the same length as the sepals.

There is questions if the species is native to the southeastern US. Its earliest records date to South Carolina in 1844 and Georgia in 1864; its unclear if these records reflect a lack of early collections or introductions (Jacono 2014).

Life history: Seeds germinate at 20°C after 6 weeks of cold stratification at 4°C; seedlings are rare; mostly reproduced by vegetative stem fragments; flowers from summer to November; seeds remain embedded in woody capsules (Okada et al. 2009; Les 2018)

Habitat: marshes, swamps, ponds, lakes, ditches, canals, and wet disturbed areas with high nitrogen and phosphorus (Godfrey and Wooten 1981; Les 2018)

Tolerances: full sunlight; depths to 1 m; elevations to 405 m; gravel, mud, sand, silt, and silty loam; tolerates dry and anaerobic conditions (Les 2018)

Community interactions: associated diatom communities shift towards shade-tolerant species under dense patches of L. hexapetala (Les 2018)

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic	Human Health	Other

Ecological impacts

Ludwigia hexapetala can grow as impenetrable mats at the water surface, blocking incoming sunlight, decreasing dissolved oxygen, and reducing available habitat for waterfowl, fish, and turtles (Alkhadher 2016; Grewell et al. 2016). It provides foraging habitat for the Giant Garter Snake, Thamnophis gigas, in Sacramento, California (Halstead et al. 2016). The species releases allelopathic chemicals, which impacts the growth rates and biomass of other plants, including Ceratophyllum demersum and Myriophyllum aquaticum (Thiébaut et al. 2019; Thouvenot et al. 2013).

Economic and human health impacts

Ludwigia hexapetala inhibits access to waterways for boating, fishing, hunting, and swimming, and it impedes important water conveyance systems including water supply canals and wetland preserves for urban and industrial water use and agricultural irrigation (Grewell et al. 2016). Dense mats of L. hexapelata inhibit the effective application of larvicides for mosquito control, which facilitates the spread of West Nile Virus (Meisler 2009).