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Sensitive Joint-vetch (Virginia Joint-vetch in NC

Sensitive Joint-vetch (Virginia Joint-vetch) in North Carolina


Aeschynomene virginica

FAMILY: Fabaceae

STATUS: Threatened

DESCRIPTION: Sensitive joint-vetch is an annual plant in the bean family native to the eastern United States. Plants typically attain heights of 1 to 2 meters in a single growing season, although they can grow as tall as 2.4 meters. The stems are single, sometimes branching near the top, and with stiff or bristly hairs. The leaves are even-pinnate, 2 to 12 centimeters (cm) long, with entire, glad-dotted leaflets. Each leaf consists of 30 to 56 leaflets. Leaflets are 0.8 to 2.5 cm long and 0.2 to 0.4 cm wide. The leaves fold slightly when touched. The yellow, irregular flowers are 1.0 to 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 3.0 to 7.0 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 North Carolina to Florida, and west to Texas and Arkansas.

RANGE AND POPULATION LEVEL: Sensitive joint-vetch is known from a total of 24 extant sites, including one in Maryland, one in New Jersey, two in North Carolina( Hyde and Beaufort Counties), and 20 in Virginia. 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. A total of 24 extant sites are currently known to exist.

HABITAT: Sensitive joint-vetch grows in the intertidal zone 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. In North Carolina, sensitive joint-vetch appears to be a species that remains 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.

REASONS FOR CURRENT STATUS: 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.

MANAGEMENT AND PROTECTION: Currently, only two sites (one in New Jersey and one in Virginia) across the entire range of the species are afforded land protection. These protected sites are still subject to off-site threats such as sedimentation and water withdrawal projects. The Virginia Department of Conservation and Recreation's Division of Natural Heritage is determining general threats on-site and off-site for the Virginia populations. They are also providing selective on-site conservation planning. Research continues into the life history and habitat requirements of the species by various entities. Germination studies are being conducted at the University of Kentucky.

Species Distribution from known occurrences. Species may occur in similar habitats in other counties.Green counties indicate observed within 20 years. Yellow counties indicate an obscure data reference to the species in the county. Red counties indicate observed more than 20 years ago.

Species distribution of the Sensitive Joint-vetch in NC

Species Location Map based on information provided by the North Carolina Natural Heritage Program.
For additional information regarding this Web page, contact Dale Suiter, in Raleigh, NC, at dale_suiter@fws.gov

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