Leafy Prairie-clover

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Leafy Prairie-clover

Dalea foliosa

StatusEndangered
ListedMay 1, 1991
FamilyLeguminosae (Fabacae)
DescriptionPerennial with pinnately compound, alternate leaves and a dense spike of purple, pea-like flowers.
HabitatEdges of cedar glades, riparian prairie remnants.
ThreatsDevelopment, dam construction.
RangeAlabama, Illinois, Tennessee

Description

Leafy prairie-clover is a perennial of the pea family with tall, erect stems, which grow to a height of 18 in (50 cm). The pinnately compound, alternate leaves are 1.4-1.8 in (3.5-4.5 cm) long and are composed of 20-30 leaflets. Small, purple flowers bloom in dense spikes at the end of the stems in late July and continue through August. In the fall the stems die but remain standing and disperse seed throughout the winter.

Flowers are hermaphroditic (male and female). Bumblebees, small bees, and syrphid flies have been observed visiting flowers. Although the species' breeding system is unknown, insect pollination, probably by bumblebee species, is required for successful seed set in other species in the genus. During one normal growing season (1990), the percent seed set in Illinois populations was greater than 70%. The number of viable seeds per head is highly correlated to inflorescence length.

Leafy prairie-clover seeds ripen by early October and disperse from the erect dead ramets from late fall to early spring. Potential dispersal vectors include wind, gravity, birds, and small mammals. Dormant seeds are capable of forming a persistent seed bank. Under natural conditions, several years are required to soften the hard seed coat, although mechanical scarification yields high germination rates in fresh seeds. Seeds from Illinois populations, however, readily germinate without scarification. Germination occurs in April and by late May the seedlings have several leaves. Adequate soil moisture is critical for seedling establishment.

Bacterial nodules form on the roots. Seedlings are killed by summer drought and frost heave and very few survive to maturity. Mature plants may not flower every year and may show decreased vegetative growth following a year of exceptionally vigorous growth.

Fire benefits Leafy prairie-clover habitat by maintaining open patches for the establishment of new plants and by controlling woody plant succession. Spring fires appear to stimulate germination and establishment, possibly by the removal of accumulated duff and subsequent creation of more openings in which buffed seeds can germinate and survive. Fall fires may increase frost heaving and indirectly affect mortality. At Lockport Prairie, overall population size has increased under both spring and fall prescribed burning regimes.

This species has also been known as Petalostemum foliosum.

Habitat

Leafy prairie-clover is found only in open limestone cedar glades, limestone barrens, and dolomite prairies which have shallow, silt to silty clay loam soils over flat and often highly fractured, horizontally bedded limestone or dolomite with frequent expanses of exposed bedrock at surface elevations typically between 550-700 ft (168-213 m). These habitats experience high surface and soil temperatures, generally have low soil moisture but are wet in the spring and fall and experience some drought in summer, and have a seasonal aspect to the flora. The distribution of glade, barren, and dry to wet dolomite prairie at any particular site is determined by subtle, local variations in soil and bedrock depths and topographic position.

Although Leafy prairie-clover can persist in partial shade, the species' preferred habitat is open sun with a soil depth from 1.6-17.7 in (4.1-45 cm) but is most abundant in 3.9-11.8 in (9.9-30 cm) of soil. The deeper, moister soils are typically at the lower portions of a slope while the more shallow, drier soils are typically near the top of a slope. Leafy prairie-clover occurs in the relatively mesic and wet-mesic portions of the soil moisture gradient, typically in association with dry washes. The wet-mesic component is probably critical to population persistence, particularly in drought years. Leafy prairie-clover roots may also penetrate the upper fractured bedrock layers, which likely provide some moisture.

Important factors that may limit the distribution of Leafy prairie-clover include shallow soils, low soil moisture, low pH, and poor competitive ability. As soil depth increases to greater than 7.9 in (20 cm), the vegetation cover increases and is more favorable to invasion by woody species. Leafy prairie-clover may be reduced or excluded from these areas by increased competition, particularly from perennial grasses and by shading effects.

Distribution

This species was first described in 1868. It has been found only in Tennessee, Alabama, and Illinois. In Tennessee it occurred in Bedford, Davidson, Marshall, Maury, Rutherford, Williamson, and Wilson counties in the central portion of the state. In Illinois it was known from six counties in the northeastern part of the state: Boone, Kane, Kankakee, La Salle, Ogle, and Will. In the late 1960s the first Alabama populations were discovered in Franklin, Jefferson, and Morgan counties. New populations were found in 1984 in Jefferson County and in 1989 in Lawrence County.

Today Leafy prairie-clover survives at only 14 sites: two in Alabama, three in Illinois, and nine in Tennessee. The Alabama populations consist of a healthy, reproducing population of about 50 plants in Morgan County and a small population on a powerline right-of-way owned by the Tennessee Valley Authority (TVA). In Illinois, three populations are known along the Des Plains River in Will County. Two of these are protected by the Will County Forest Preserve District; the third site adjoins a right-of-way for a proposed highway. In Tennessee the species survives in Bedford, Davidson, Maury, Rutherford, Williamson, and Wilson counties. In Rutherford County a population of 25-30 plants occurs in a state park. Two other sites in the county support populations of two plants each, neither of which is expected to survive. A single Davidson County population is on land slated for development and will probably be lost. In Williamson County, a small population occurs on land owned by The Nature Conservancy, although a portion of the population grows on adjacent private land. Two populations of 20-30 plants occur in Wilson County on land managed by the Tennessee Department of Conservation. In Bedford County a healthy population of about 250 plants was discovered during 1990 field surveys. The largest and healthiest population in the state, consisting of about 650 plants, is in Maury County on land owned by the TVA. Another population of about 50 plants is also found in the county. From 1987 through 1990 the Tennessee Department of Conservation made extensive field surveys in search of new Leafy prairie-clover populations. More than 200 potential sites were examined and only two new populations were discovered.

Threats

Most Leafy prairie-clover populations are small and are threatened by collecting. One historic population at Altorf Island, Illinois, was eliminated by overcollecting.

In Illinois there is a horticultural interest in the species because it is rare and is easily propagated from seed. At least one nursery is known to sell Leafy prairie-clover from a cultivated source. Natural populations could be threatened by illegal (un-permitted) or inappropriate seed-collecting if natural seed production is low due to small population size, high rates of herbivory, or drought conditions.

At least one population, in Morgan County, Alabama, is likely to be extirpated by road maintenance and the installation of new storm sewers. Several additional populations are at some risk due to their proximity to existing roads. Although reportedly bulldozed, there are still plants at the Wood-mont Boulevard site in Nashville. Unless these plants are salvaged, the population will undoubtedly be lost to development. Two populations occur under active power transmission lines. The habitats are kept open by right-of-way management, but the populations are at risk from cleared brush being piled on the plants, the nonselective use of herbicides during the growing season, and damage caused by large trucks.

Thirty to fifty percent of the Leafy prairie-clover plants in Maury, Marshall, and Bedford counties, Tennessee, will be lost if the Duck River is impounded to the originally proposed 630-ft (192-m) full-pool elevation.

Off-road vehicles cause extensive habitat damage and threaten any population that has available access points. Three sites, Romeoville Prairie and Keepataw Forest Preserve in Illinois and Cedars of Lebanon State Forest/Park in Tennessee, have ongoing off-road vehicle problems. No actions have been taken to secure the populations from this threat except for the posting of signs in the state forest.

Severe drought conditions may drastically reduce or entirely eliminate populations without seed banks. Populations that are large (more than 500 plants), have extensive seed banks, and occur in sites with moist habitats are buffered from extirpation and rebound more rapidly in the year following a drought. Some plants respond to drought by dormancy, which may permit the species to survive droughts.

Leafy prairie-clover does not persist where there is intense grazing. The eastern cotton-tail rabbit and, to a lesser extent, the white-tailed deer selectively feed on flowering ramets and can significantly reduce reproductive success. Intense and persistent grazing reduces annual seed production and seed bank contributions.

The invasion of woody species poses a very serious threat to Leafy prairie-clover. The species is intolerant of shade but may persist as a seed bank, although the factors controlling the development and longevity of the seed-bank are unknown. For example, new patches of Leafy prairie-clover seedlings appeared after brush removal at Lock-port Prairie in Illinois and Sneed Road Cedar Glade in Tennessee, two sites containing large extant populations.

Conservation and Recovery

Several attempts to reintroduce Leafy prairie-clover to Altorf Island, Illinois, have failed due in part to severe summer drought conditions and the reduction of historic gravelly bank habitat, the result of heavy canary reed grass infestation. No seedlings have been observed from two seeding attempts, and none of the 105 plants transplanted in 1990 survived. Only one of the five large plants transplanted in October 1991 was observed in August 1992.

Leafy prairie-clover has been introduced into three prairie restorations. Five seedlings originally planted into wet-mesic prairie in 1985 at the College of DuPage have survived and reproduced; there are now approximately 20 plants in this area. Eight additional transplants planted in 1988 and 1991 still persist. While this introduced population has educational value, it does not contribute to the species' recovery because plants are not in natural or historically appropriate habitats within the species' geographic range in Illinois. Over time, this population can be expected to decline.

Twelve Leafy prairie-clover seedlings were transplanted into degraded and overgrazed mesic to drymesic gravel prairie at the Waterfall Glen Forest Preserve located approximately 2.75 mi (4.4 km) upstream from the population at Keepataw Preserve. By September 1992 only two plants remained. Although within the species' range, this site may be too degraded, dry, and small to support a viable population.

In 1990, 50 juvenile Leafy prairie-clovers grown from seeds collected from the Lockport Prairie population were planted into re-created gravel and dolomite prairie at the Morton Arboretum in Lisle, Illinois. This prairie creation features endangered and threatened plants in simulated natural habitats and functions both as source material for restorations as well as an educational exhibit. These Leafy prairie-clover plants flowered and produced seeds in 1991 and 1992. Approximately 2,500 seeds were collected from Will County populations and were provided to the Holden Arboretum in Mentor, Ohio, for long-term storage as part of the Center for Plant Conservation's cooperative program.

In Tennessee, most of the Williamson County site is owned by The Nature Conservancy. The large Maury County population, which is owned by TVA, will be damaged if the Columbia Dam on the Duck River is completed according to the original proposal. TVA is currently evaluating the impact of the dam on federally Endangered mussels in the area. If the proposal is modified to allow for a lower floodpool level, the Leafy prairie-clover population would not be affected by the dam. The higher flood-pool level, however, would destroy about half of the population.

Contacts

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
Federal Building
Ft. Snelling
Twin Cities, Minnesota 55111
http://midwest.fws.gov/

Regional Office of Endangered Species
U. S. Fish and Wildlife Service
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Baskin, J. M., and C. Baskin. 1973. "The Past and Present Geographical Distribution of Petalostemon foliosus and Notes on Its Ecology." Rhodora 756:132-140.

Kral, R. 1983. A Report on Some Rare, Threatened, or Endangered Forest-related Vascular Plants of the South. USDA, Forest Service, Technical Publication RS-TP2.

Kurz, D. R., and M. L. Bowles. 1981. "Report on the Status of Illinois Vascular Plants Potentially Endangered or Threatened in the United States." Natural Land Institute, Rockford, Illinois.

Smith, D. K., and B. E. Wofford. 1980 "Status ReportPetalostemum foliosum Gray (Dalea foliosa [Gray] Barneby)." U.S. Fish and Wildlife Service, Atlanta.

Tennessee Valley Authority. 1988. "Biological Asessment of Columbia Dam Alternatives, Duck River, Tennessee." Knoxville, Tennessee.

U. S. Fish and Wildlife Service. September 30, 1996. "Recovery Plan for the Leafy prairie-clover." U. S. Fish and Wildlife Service, Atlanta, 92 pp.