Astragalus robbinsii var. jesupii
|Jesup's milkvetch, Robbins milkvetch|
|Egglest. & Sheldon|
|Elizabeth J. Farnsworth|
The following Participating Institutions are custodians for this species in the CPC National Collection:
New England Wild Flower Society
The conservation of Astragalus robbinsii var. jesupii is fully sponsored.
Elizabeth J. Farnsworth contributed to this Plant Profile.
Astragalus robbinsii var. jesupii is an extremely rare member of the bean family, found only at three sites along a 15-mile stretch of the middle Connecticut River in New Hampshire and Vermont. This plant is found only in areas that receive periodic ice-scouring that clears competing vegetation from riverbanks. Although it has fairly specialized habitat requirements, it is somewhat surprising that the species is so rare, as it occupies very little of the potential habitat available to it. Its tenuous existence is threatened by a number of activities, like damming, that alter the hydrological and disturbance regime of a waterway; trampling by recreational boaters; and historical over-collecting that may have significantly reduced its numbers.
Research and Management Summary:
Fairly limited research has been conducted on this taxon, but populations are regularly monitored, and the New England Wild Flower Society has undertaken a reintroduction project.
Astragalus robbinsii var. jesupii grows 20 to 60 cm (0.65 - 2.0 ft) tall from a thick rhizome or taproot. Like many legumes, it has compound leaves, with 9 to 17 sparsely hairy leaflets each about 1 cm (0.4 in) long. Pale purple to violet flowers 1 cm across are produced in late May to mid-June, and have a papery texture. In late June, plants produce beaked legumes ("pea pods") approximately 2 cm (0.8 in) long, which are covered with small black hairs.
Distribution & Occurrence
- New Hampshire
Astragalus robbinsii var. jesupii is reported only from rocky shores of the Connecticut River composed of phyllite or chlorite schist. Like other members of the Astragalus robbinsii complex, this variety is associated with rock that is rich in calcium and magnesium (U. S. Fish and Wildlife Service 1989, NatureServe 2001). The plants occur on moderately steep bedrock slopes that face east or southwest, in crevices and shelves where some litter and sediment has been deposited. The river shores where this plant can be found are periodically scoured by ice breaking up and floating down the Connecticut River in spring; thus, plants are sparse and few species that cannot tolerate such disturbance are present.
Other associated species recorded in this boreal river shore outcrop community include: Senecio pauperculus (ragwort), Toxicodendron radicans (poison ivy), Poa compressa, Chrysanthemum leucanthemum, Hypericum perforatum, Solidago canadensis, Campanula rotundifolia, Erigeron pulchellus, Galium mollugo, Alnus rugosa, Ulmus americana, and Salix spp., as well as several rare or specialized calcium-loving plant species such as Allium schoenoprasum var. sibiricum, Carex garberi, Hypericum pyramidatum, and Tofieldia glutinosa.
|Three populations are recorded: two in New Hampshire and one in Vermont. Plant numbers fluctuate dramatically from year to year; total observed populations have hovered between 200 and 900 plants (U. S. Fish and Wildlife Service 1989, The Nature Conservancy [TNC], New Hampshire Chapter 2001).|
Conservation, Ecology & Research
Flowering commences in mid-May and usually ends by late May to mid-June and most fruits have been released by August (Brackley et al. 1990). According to Brackley et al. (1990), pollinators include a common bumblebee (Bombus vagans vagans) and another species of bee (Cnemidandrena hirticincta). However, the plant is also noted to be self-compatible, based on the results from pollinator-exclusion studies (Brackley et al. 1990).
Seeds from the ripened fruits appear to sink, but dispersal distances from parent plants have not been determined. Sporadic long-distance seed dispersal may be important if the species acts as a metapopulation (a string of genetically linked, ephemeral sub-populations or demes that often occur in disturbed environments). Interestingly, some seeds germinate while still on the parent plant, if the plants are submerged during wet years (Brackley et al. 1990). Seeds will also germinate with no pre-treatment following collection (Brumback 1989).
The best ex situ germination occurs when seeds have been lightly scarified with sandpaper, possibly mimicking the spring scouring experienced by seeds in the wild (W. E. Brumback, New England Wild Flower Society, personal communication). Seed in storage can remain viable for more than six years, but the presence of a seed bank at the New Hampshire and Vermont sites has not been confirmed. Seedlings appear to be rare in the wild.
Deer and rodents can feed on the plants, and have eaten plants at various sites (Brackley et al. 1990). Plants also may be vulnerable to drought during especially dry summers (New Hampshire TNC 2001).
Altered hydrology (due to damming, engineering [Ferrick et al. 1988], naturally changing river courses, or climatic change) that results in changing ice scour patter
The New England Wild Flower Society (NEWFS) in Framingham, Massachusetts has determined reliable methods for germinating plants. Plants at NEWFS have germinated readily and survive to flowering. However, long-term survival after flowering has been problematic. Plants are growing in the NEWFS garden.
Phil Nothnagle (Consulting Botanist, Vermont) has also worked on propagation of the species (New Hampshire TNC 2001).
Reintroduction of Astragalus robbinsii var. jesupii has been undertaken by the New England Wild Flower Society. After several years of battling floods and drought, and developing techniques for introducing both plants and seed, this reintroduction program is gaining ground (New Hampshire TNC 2001; Brumback, personal communication).
Natural Heritage Programs and The Nature Conservancy of both states are working to protect current and potential riverine habitat for Astragalus robbinsii var. jesupii; one New Hampshire site has been protected by a conservation agreement with the landowner (U. S. Fish and Wildlife Service 1989).
Studies of the effects of invasive plant species on survivorship and reproduction of Astragalus robbinsii var. jesupii
Quantitative population viability analysis from the monitoring data collected on populations
Studies to determine the causes of poor seedling establishment at sites
Program, Nongame and Natural Heritage. 2000. Rare and Uncommon Native Plants of Vermont. Waterbury, Vermont: Vermont Department of Fish and Wildlife.