|sensitive joint-vetch, Virginia joint-vetch|
|Elizabeth J. Farnsworth|
The following Participating Institutions are custodians for this species in the CPC National Collection:
New England Wild Flower Society
Brooklyn Botanic Garden
The conservation of Aeschynomene virginica is fully sponsored.
Elizabeth J. Farnsworth contributed to this Plant Profile.
Sensitive joint-vetch, so-named because its leaves fold slightly when touched, inhabits freshwater tidal marshes along the mid-Atlantic coast. Only 24 populations remain in New Jersey, Maryland, North Carolina, and Virginia, and the species has shrunk substantially from its former distribution, which once also included Pennsylvania and Delaware. Factors contributing to the decline of Aeschynomene virginica include: road construction; residential, commercial and industrial development; water pollution; bank erosion; and motor boat traffic -- all associated with extremely rapid population growth in the mid-Atlantic states. Interestingly, Aeschynomene virginica has frequently been confused in the scientific literature with the invasive weed, Aeschynomene indica, and referred to erroneously as an agricultural pest! Recent genetic and taxonomic studies have resolved this confusion (Carulli and Fairbrothers 1988, Isley 1990).
Research and Management Summary:
This species has been relatively well studied. A number of sites in the United States are protected by The Nature Conservancy, and some work is being done to remove invasive species.
Aeschynomene virginica is a robust, annual herb in the pea family that grows up to 2 meters (6 feet) tall. It produces alternate, compound leaves with 30-56 leaflets along the stem that are slightly hairy and dotted with glands. Flowers are pea-like, about 1 cm (0.4 in) long, and yellow with prominent red veins; flowers appear in late July and continue into autumn. Fruits are segmented pods about 6 cm (2.3 in) long and are produced until first frost.
Distribution & Occurrence
- New Jersey
- North Carolina
Aeschynomene virginica is native to freshwater tidal marshes of the mid-Atlantic states (USFWS 1992). These marshes exhibit twice-daily tides, but occur far enough upstream that they are nearly fresh or barely brackish in water chemistry. Salinity of one site in New Jersey ranges from 0.7 to 0.8 ppt with an average pH of 4.4. (NatureServe 2001). Only a small group of plants can tolerate this tidal inundation; thus, freshwater tidal marshes are home to many specialized and rare species. Aeschynomene virginica grows low in the intertidal zone where soils may be mucky, sandy, or gravelly (Department of Conservation and Recreation 1997). Aeschynomene virginica may perform best in areas of the marsh where competition with other plants is reduced -- for example, newly accreting shores or openings created by wrack deposition or muskrat activity (Department of Conservation and Recreation 1997).
In North Carolina, A. virginica has been found in a few road-side ditches and wet corn fields, but these are not considered stable populations (Leonard 1985, USFWS 1992). Biological inventories of available freshwater tidal marsh habitat in North Carolina did not turn up additional populations, so the outlook for the taxon in that state is uncertain.
Plant species commonly associated with A. virginica include: Zizania aquatica, Peltandra virginica, Pontederia cordata, Bidens laevis, Polygonum arifolium, P. sagittatum, and Leersia oryzoides, and, in southern areas, another similar legume, Chamaecrista fasciculata var. macrosperma (Department of Conservation and Recreation 1997, NatureServe 2001).
|24 populations of Aeschynomene virginica are documented in the original recovery plan, but one historic population in Virginia was rediscovered in 2001.
New Jersey supports several thousand plants in 2 populations: one in the Maurice River watershed and one near the Hudson (American Museum of Natural History 2001, Joseph Patt [The Nature Conservancy] unpublished data).
Maryland has one population of several hundred plants.
North Carolina's ditch populations are very small and variable from year to year.
Virginia reports approximately 5,000 plants altogether.
Therefore, the global population is on the order of 10,000 plants (USFWS 1992). Population numbers fluctuate widely among years, making global population estimates problematic.
Conservation, Ecology & Research
Conspicuous yellow flowers remain on the plant throughout the summer months. Insects are the primary pollinators: bumblebees (Bombus spp.), leaf-cutter bees (family Megachilidae), and the least skipper (Ancylozypha numitor) have been observed on plants in New Jersey, according to Dr. Joeseph Patt of The Nature Conservancy.
Seeds are produced in pods, and segments of the pods can float and potentially disperse in water. However, seeds commonly fall very close to the parent plant (Griffith 2001). Seedlings may preferentially germinate in rafts of floating plant material that have been deposited on the river bank (Bruederle and Davison 1984). Such floating wrack may kill existing plants and open new bare space that can be colonized by A. virginica. Muskrats may also create such openings (Department of Conservation and Recreation 1997). As an opportunistic colonizer of bare space, an apparently poor competitor with other plants, and a plant that occurs in periodically disturbed, riparian sub-populations that may exchange propagules, A. virginica may exhibit metapopulation dynamics where it occurs (Griffith 2001).
Like its more common relatives, A. indica and A. americana (Grant 1996), Aeschynomene virginica may form nodules with symbiotic, nitrogen-fixing bacteria, but these dynamics have not been studied. If so, the species may be very sensitive to changes in the nitrogen content of wetland soils due to increasing nutrient inputs in water and rising atmospheric nitrogen deposition, problems that are especially severe in the mid-Atlantic region.
Habitat destruction due to shoreline stabilization, rip-rapping, channelization, and dredging to support residential, commercial, and industrial development
Shoreline erosion due to boat
The Chloroplast DNA (cDNA) sequence has been published for the taxon (GenBank release 123.0, April 2001)
Botanist Gerry Moore (Brooklyn Botanical Garden) has surveyed extensive areas of the Maurice River watershed in New Jersey for additional populations of Aeschynomene virginica.
Graduate student, Alan Griffith (University of Maryland) is completing his doctoral dissertation on metapopulation dynamics of Aeschynomene virginica. He has transplanted seedlings of the plant to research plots and notes that survivorship and seed production of A. virginica are significantly higher in areas where other vegetation has been cleared. Survivorship of seedlings is still below 20%, however.
Jerry M. Baskin (University of Kentucky) received funding from the U. S. Fish and Wildlife Service to study seed germination in A. virginica. The species germinates without dormancy following scarification and treatment with 30 oC/15 oC temperatures in the laboratory (Baskin and Baskin 1998: 494).
Student Elizabeth Mountz presented an abstract discussing the identification of essential habitat for A. virginica at the 2000 Student Research Conference for the Virginia Space Grant Consortium, Old Dominion University, Norfolk, Virginia (contact conference organizer, Heidi B. Davis [firstname.lastname@example.org] for information on obtaining conference proceedings).
Biologist Joe Patt (The Nature Conservancy, Delaware Bayshores Office) is conducting studies of population dynamics, pollination and herbivory on the Maurice River watershed population of A. virginica. He notes high variability in population numbers from year to year (fluctuating from thousands to tens of thousands of plants), and is devising a consistent transect method for censusing plants.
Professor Peter F. Straub of Richard Stockton College of New Jersey is measuring homozygosity levels in populations of A. virginica.
The New England Wild Flower Society and partners in mid-Atlantic states have collected seeds from several populations. Accessions are also held by the National Seed Storage Laboratory in Fort Collins, Colorado.
The Nature Conservancy in New Jersey is removing invasive Phragmites australis near one population along the Manumuskin River (contact Joe Patt, TNC, email@example.com for more information)
A survey of the prevalence and impacts of invasive species on existing populations is needed, and the effect of invasive species removal on this species needs to be monitored
Studies of the impacts of nutrient loading on ecophysiology, symbiotic nodulation, and fitness of A. virginica.
Studies to inform the creation of habitat or optimal conditions for establishment of A. virginica
Study of the impacts of rising sea level (increased salinity) on A. virginica and other freshwater wetland plant species
Basic information on pollinator identity, herbivores, nodulation symbionts, and other factors influencing establishment and fitness
Propagation of A. virginica for wetland restoration and possible mitigation would also be beneficial
Baskin, C.C.; Baskin, J.M. 1998. Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. San Diego, California: Academic Press.