Sensitive Joint-vetch (Aeschynomene virginica)
Family: Pea (Fabaceae)
Federal Status: Threatened, listed May 20, 1992
Best Search Time: mid-July through October
Description: Sensitive joint-vetch (Aeschynomene virginica) is an annual plant in the pea family (Fabaceae) that is native to the eastern United States. Plants typically attain heights of 3.3 – 6.6 feet (ft) (1 - 2 meters; m) in a single growing season, although they can grow as tall as 7.8 ft (2.4 m). The stems are single, sometimes branching near the top, and with stiff or bristly hairs. The leaves are even-pinnate, 0.8 – 4.7 inches (in) (2 - 12 centimeters; cm) long, with entire, gland-dotted leaflets. Each leaf consists of 30 to 56 leaflets. Leaflets are 0.3 – 1 in (0.8 - 2.5 cm) long and 0.08 – 0.16 in (0.2 - 0.4 cm) wide. The leaves fold slightly when touched. The yellow, irregular flowers are 0.4 – 0.6 in (1.0 - 1.5 cm) across, streaked with red, and grow in racemes (elongated inflorescence with stalked flowers). The fruit is a loment with 4 to 10 one-seeded segments, turning dark brown when ripe. Fruits are 1.2 - 2.8 in (3 - 7 cm) long and shallowly scalloped along one side.
Plants flower from July through September and occasionally into October. In Autumn, senescence may be triggered by the drop in water temperature or by salinity intrusion due to a decrease in freshwater flow. Bumblebees have been observed pollinating the flowers. Fruits form shortly after the first signs of flowering in July. Although flowering continues until late Fall, production of vigorous fruits appears to decline significantly by mid-October. Seed maturation begins in August and continues through October. Germination takes place from late May to early June. Seedlings grow quickly, approximately doubling in size every 2 weeks during the first 6 weeks.
This species has been confused with other members of the genus, especially A. indica and A. rudis. These two species, not native to the United States, have spread northward into North Carolina in recent years, where their ranges now overlap with that of this threatened species. A. indica is common in wet agricultural areas from Virginia to Florida, and west to Texas and north to Missouri. A. rudis has a scattered distribution from Pennsylvania to Florida to California.
Habitat: Sensitive joint-vetch typically grows in the intertidal zone of coastal marshes where plants are flooded twice daily. The species seems to prefer the marsh edge at an elevation near the upper limit of tidal fluctuation. It is usually found in areas where plant diversity is high (50 species per acre) and annual species predominate. Bare to sparsely vegetated substrates appear to be a habitat feature of critical importance to this plant. As an annual, it requires such microhabitats for establishment and growth. Such areas may include accreting point bars that have not yet been colonized by perennial species, low swales within extensive marshes, or areas where muskrats have eaten most of the vegetation. It appears to remain at a particular site for a relatively short period of time, and maintains itself by colonizing new, recently disturbed habitats where it may compete successfully among other early-successional species. It is frequently found in the estuarine meander zone of tidal rivers where sediments transported from upriver settle out and extensive marshes are formed. The substrate may be sandy, muddy, gravelly, or peaty. In North Carolina, Sensitive joint-vetch is most often found in roadside ditches, often with some connection to nearby brackish marshes.
Distribution: Sensitive joint-vetch is known from Maryland, New Jersey, Virginia and North Carolina. It was historically known from Pennsylvania and Delaware. The species shows considerable annual fluctuation in population numbers, varying in at least one case from approximately 50 to 2,000 individuals over a 3-year period. Although populations do fluctuate, there is an apparent trend for large populations to remain large and small populations to remain small.
Threats: The extirpation of Sensitive joint-vetch from Delaware and Pennsylvania and its elimination from many sites in other States can be directly attributed to habitat destruction. Many of the marshes where it occurred historically have been dredged and/or filled and the riverbanks stabilized with bulkheads or riprap. Other threats include sedimentation, competition from exotic plant species, recreational activities, agricultural activities, mining, commercial and residential development with associated pollution and sedimentation, impoundments, water withdrawal projects and introduced insect pests.
References:Buchanan, M.F. and J.T. Finnegan. 2010. Natural Heritage Program List of the Rare Plant Species of North Carolina. NC Natural Heritage Program, Raleigh, NC.
U.S. Fish and Wildlife Service. 1995. Sensitive Joint-vetch (Aeschynomene virginica) Recovery Plan. U.S. Fish and Wildlife Service, Hadley MA. 55 pp.
For More Information on Sensitive Joint-Vetch...
- U.S. Fish and Wildlife Service Environmental Conservation Online System
- Sensitive Joint-vetch Recovery Plan
- U.S. Department of Agriculture Natural Resource Conservation Service Plants Database
- Center for Plant Conservation species profile
- Citizens United to Protect the Maurice River
Dale Suiter, Fish and Wildlife Biologist, 919-856-4520 ext. 18
Species profile revised on July 26, 2011.