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.
