Identification: According to Godfrey and Wooten (1981):
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.
Native Range: Ludwigia hexapetala is native to South America.
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).
† Populations may not be currently present.
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)
Impact of Introduction:
Summary of species impacts derived from literature review. Click on an icon to find out more...
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).
References: (click for full references)
Alkhadher, M. 2016. South American aquatic weed is here to stay at Eugene’s Delta Ponds, but city succeeds in substantially knocking it back. The Register-Guard. Eugene, OR. http://registerguard.com/rg/news/local/34662990-75/story.csp. Created on 08/11/2016. Accessed on 08/11/2016.
Godfrey, R.K., and J.W. Wooten. 1981. Aquatic and Wetland Plants of the Southeastern United States, dicotyledons. University of Georgia, Athens, GA.
Grewell, B.J., M.D. Netherland, and M.J. Skaer Thomason. 2016. Establishing research and management priorities for invasive water primroses (Ludwigia spp.). U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS. https://apps.dtic.mil/sti/pdfs/AD1002917.pdf.
Halstead, B.J., P. Valcarcel, G.D. Wylie, P.S. Coates, M.L. Casazza, and D.K. Rosenberg. 2016. Active season microhabitat and vegetation selection by giant gartersnakes associated with a restored marsh in California. Journal of Fish and Wildlife Management 7(2):397-407. https://doi.org/10.3996/042016-JFWM-029.
Jacono, C. 2014. A note on Florida's latest waterprimrose, Ludwigia hexapetala. Aquatics 36(1):15-16. https://plants-archive.ifas.ufl.edu/wp-content/uploads/files/caip/pdfs/LudwigiaHexapetala-fromAquaticsSpring2014.pdf.
Les, D.H. 2018. Aquatic dicotyledons of North America: ecology, life history, and systematics. CRC Press, Boca Raton, FL.
Meisler, J. 2009. Lessons from Ludwigia control in Sonoma County. Cal-IPC News. Berkeley, CA. 17 (2):4-5. https://www.cal-ipc.org/docs/resources/news/pdf/Cal-IPC_News_Summer09.pdf.
Okada, M., B. Grewell, M. Jasieniuk. 2009. Clonal spread of invasive Ludwigia hexapetala and L. grandiflora in freshwater wetlands of California. Aquatic Botany 91:123-129.
Thiébaut, G., L. Thouvenot, and H. Rodríguez-Pérez. 2018. Allelopathic effect of the invasive Ludwigia hexapetala on growth of three macrophyte species. Frontiers in Plant Science 9(1835):1-10. https://doi.org/10.3389/fpls.2018.01835.
Thiébaut, G., H. Rodriguez-Perez, and O. Jambon. 2019. Reciprocal interactions between the native Mentha aquatica and the invasive Ludwigia hexapetala in an outdoor experiment. Aquatic Botany 157:17-23. https://doi.org/10.1016/j.aquabot.2019.05.005.
Thouvenot, L., C. Puech, L. Martinez, J. Haury, G. Thiébaut. 2013. Strategies of the invasive macrophyte Ludwigia grandiflora in its introduced range: Competition, facilitation or coexistence with native and exotic species? Aquatic Botany 107:8-16. https://doi.org/10.1016/j.aquabot.2013.01.003.
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.