- Scientific name: Ludwigia polycarpa Short & R.Peter
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Endangered (MA Endangered Species Act)
Description
Many-fruited seedbox (Ludwigia polycarpa) is a much-branched, 2-10 dm (7 in-3 ft) tall, semi-aquatic herbaceous perennial with small, inconspicuous, 4-sided greenish flowers occurring in the axils of the upper leaves. This member of the evening primrose family (Onagraceae) is found in swamps, sloughs, marshes, and wet prairies.
Many-fruited seedbox has erect, 4-angled branching stems with sessile (stemless), alternate leaves that are lanceolate or linear-lanceolate in shape and 4-10 cm (~1.5-4 in) long.
The flowers are sessile or on obscure pedicels (stems) less than 1 mm long in the upper leaf axils of elongate, leafy spikes. Petals, when present, are minute and greenish (often it has no petals) and one arises from the top of each side of a 4-sided cup-like receptacle (hypanthium) surrounding the ovary. Four green sepals are longer (2.5-4.5 mm) and are also arranged at the top of the ovary (Ramstetter and Mott-White, 2000).
The fruit is a rounded 4-sided or shallowly grooved, short-cylindric capsule that is 4-7 mm long (0.13-0.25 in.) and 3-5 mm (0.12–0.2 in.) in diameter. The capsule is smooth (glabrous) and contains many seeds. A pair of short, leaf-like appendages called bracteoles are attached above the base of the hypanthium.
The lack of definite pedicels for the flowers and fruits differentiates L. polycarpa from the similar L. alternifolia, which has pedicels 3-5 mm (0.12–0.2 in) long. Many-fruited seedbox might be confused with species in the loosestrife genus (Lythrum). Plants in Lythrum usually have 6-merous (6 petals, 6 sepals) flowers with red-purple to white petals, 2-celled capsules and opposite leaves.
Flowers, photo by Arthur Haines, Native Plant Trust
Flowers showing bracts on side of ovary, photo by Arthur Haines, Native Plant Trust
Life cycle and behavior
Many-fruited seedbox is a short-lived stoloniferous (surface-running) perennial. It blooms in late summer to early fall, releasing seeds in the fall, typically October to November as the plant senesces. The scientific name “polycarpa” refers to the fact that it produces many seeds.
Many-fruited seedbox reproduces through sexual and asexual means. It is self-compatible, though when the flowers first open the stamens initially arch out, holding the pollen away from the stigma. As the day progresses the stamens will arch in so that the pollen comes in contact with the sticky surface of the stigma. Insects may help with pollination but the extent that occurs is not known. Hybrid plants are occasionally observed so there is some cross-pollination with related species via insect vectors.
Many-fruited seedbox stores energy and nutrients in stolons over the winter and resprouts in the spring. Wagner and Hoch (2021) state, “The basal stolons formed by Ludwigia polycarpa tend to be shorter, more condensed, and more branched than those found in other species, and may be a morphological adaptation to perennial survival in the colder areas in which it grows.”
Leaves, photo by Arthur Haines, Native Plant Trust
Fruits, Photo by Katy Chayka, MinnesotaWildflowers.info
Population status
Many-fruited seedbox is listed under the Massachusetts Endangered Species Act as Endangered. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors.
The Massachusetts Natural Heritage and Endangered Species Program has records of 13 populations from 4 counties: Franklin, Hampden, Hampshire, and Middlesex. Ten of these populations have been observed within the last 25 years.
Distribution and abundance
The documented range of many-fruited seedbox extends from Maine south to Alabama, west through southern Ontario to southeastern Minnesota south to northeastern Arkansas, eastern Nebraska and eastern Kansas.
In the northeast, many-fruited seedbox is considered critically imperiled in Massachusetts, New York, Pennsylvania and Vermont, and may be extirpated in Connecticut and West Virginia. It is also considered critically imperiled in Kansas and in Idaho where a disjunct population (perhaps introduced) occurs. It only occurs in Ontario in Canada, where it is considered imperiled.
Distribution in Massachusetts. 2000-2025. Based on records in the Natural Heritage Database.
Habitat
In Massachusetts, many-fruited seedbox occurs almost exclusively in river floodplains, where it inhabits wet, exposed mud in oxbows and depressions within the zone of annual flooding. Canopy cover at the floodplain sites varies from nearly open to closed and is composed mainly of silver maple (Acer saccharinum), green ash (Fraxinus pennsylvanica), pin oak (Quercus palustris), and/or black willow (Salix nigra). Other frequent associates are northern water-plantain (Alisma subcordatum), false nettle (Boehmeria cylindrica), false water-pepper (Persicaria hydropiperoides), ditch-stonecrop (Penthorum sedoides), water purslane (Ludwigia palustris), swamp candles (Lysimachia terrestris), and buttonbush (Cephalanthus occidentalis).
Healthy habitats are vital for supporting native wildlife and plants. Explore habitats and learn about conservation and restoration in Massachusetts.
Threats
The primary threats to many-fruited seedbox include the loss of floodplain habitat, succession and canopy closure, invasive species, changes in hydrology and Canada geese and deer herbivory. Changes in the flooding regime may be the primary concern for this species as climate change causes larger floods and longer droughts. Both may negatively impact the populations of many-fruited seedbox. With populations spread out across the state, one stochastic event, such as a severe flood, extended drought, or accidental herbicide application, could wipe out a population and there is no nearby population to re-colonize an area.
Conservation
Survey and monitoring
Many of the most recent surveys of known populations have not relocated the species. Additional surveys of these populations are needed, as plants may have been overlooked, or growing conditions were not appropriate for seed germination. The best time to survey many-fruited seedbox is late summer, in August and September, when the plants are most visible and may be in bloom and fruit. Each stem growing from the ground is a single genet.
Management
As with many rare species, exact needs for management of many-fruited seedbox are not known. The following comments are based primarily on observations of populations in Massachusetts. Undisturbed floodplain habitat is rare throughout the state due to housing development and to conversion of these highly fertile areas to agricultural land.
The success of many-fruited seedbox in Massachusetts depends on the protection of floodplain habitat, rather than species-specific management techniques. Management needs are defined site by site. Many-fruited seedbox has been observed in higher numbers and in healthier condition when in sun rather than shade. It is likely that several populations need invasive plant control and partial opening of the canopy.
Research needs
Several populations of many-fruited seedbox have not been relocated recently during survey events. It is not clear why populations have declined and are disappearing. Primary research needs for this species are surveys of all the populations in Massachusetts and to assess risk factors for their decline. It is primarily a mid-western species and is at its eastern extent in Massachusetts and Maine.
It is not known how long the seed of this species remains viable in the soil, or if specific soil conditions enhance seed viability over the long term. Common garden experiments may help determine how to help this species survive. It is thought that the seed might float when released from the capsules; this needs to be confirmed and the extent and distance seed might move. Other aspects of Many-fruited seedbox life history should be studied to determine potentially vulnerable stages, so that actions can be taken to protect the species more fully.
Specific pollinators for this species are not known; research is needed to determine these, how frequently they visit populations, and if and how these pollinators are impacted by climate change.
References
Crow, G.E. and C.B. Hellquist. Aquatic and Wetland Plants of Northeastern North America. Volume Two Angiosperms: Monocotyledons. 2000. The University of Wisconsin Press. Madison Wisconsin.
Fernald, M. L. 1950. Gray’s Manual of Botany, Eighth (Centennial) Edition—Illustrated. American Book Company, New York.
Gleason, Henry A., and Arthur Cronquist. Manual of Vascular Plants of Northeastern United States and Adjacent Canada, Second Edition. Bronx, NY: The New York Botanical Garden, 1991.
Haines, A. 2011. Flora Novae Angliae – a Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. New England Wildflower Society, Yale Univ. Press, New Haven, CT.
MissouriPlants.com. https://www.missouriplants.com/Ludwigia_polycarpa_page.html Accessed 4/7/2026.
Native Plant Trust. 2014. NORM Phenology Information.
NatureServe. 2026. NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. Accessed 4/7/2026.
POWO (2026). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; https://powo.science.kew.org/ . Accessed 4/7/2026.
Ramstetter, J. and J. Mott-White. 2001. Ludwigia polycarpa (Many-fruited False Loosestrife) Conservation and Research Plan. New England Plant Conservation Program, Framingham, Massachusetts, USA
Wagner, Warren L. and Peter C. Hoch. 2021. ONAGRACEAE Jussieu, Evening Primrose Family. In: Flora of North America Editorial Committee, eds. Flora of North America North of Mexico. 19+ vols. New York and Oxford. Vol. 10, pp 70-101.
Contact
| Date published: | April 30, 2025 |
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| Last updated: | May 12, 2026 |