Crenulate Lead-plant

Amorpha crenulata

Description

Crenulate lead-plant, Amorpha crenulata, is a shrub growing up to 5 ft (1.5 m) in height. Compound leaves bear 25-33 leaflets, arranged alternately along the branching stems. The flower is formed of a single petal, 0.25 in (6 mm) long. Flowers are loosely arranged in clusters along the ends of the stems (a raceme).

Habitat

Crenulate lead-plant grows in poorly developed soils, composed mainly of a thin layer of sand with a substrate of porous limestone known as Miami oolite. Erosion of this underlying limestone results in frequent solution holes and jagged surface features. Many plants are rooted in cracks and crevices in the rock.

Plant populations are restricted to a low ridge that reaches elevations of only about 16 ft (5 m) but provides a markedly different habitat for plants and animals from that of the marshes and wet prairies that dominate the region. The predominant vegetation on the ridge is southern slash pine with a lush understory of saw palmetto, silver palm, poison-wood, rough velvetseed, and wax myrtle.

Distribution

Historically, crenulate lead-plant occurred throughout pine rockland habitat in the Miami-Coral Gables area. This habitat consists of the south Florida limestone ridge, which extends 65 mi (105 km) from southeastern Broward County to Long Pine Key in Everglades National Park.

Crenulate lead-plant is found only at a three sites on remnant habitat within the Miami City limits (Dade County). Population figures have not been published, but fewer than 100 of the plants were thought to survive as of 1988. Of the three sites, one small population occurs on a vacant lot in a housing subdivision and is expected to die off; a second small population is found along the bank of a canal and suffers from right-of-way maintenance mowing and herbicide application. The third and largest group of plants is found in Bird Drive Park, which falls under the jurisdiction of Dade County.

Threats

Florida pine rockland habitat has undergone extensive urbanization and agricultural development. Botanists have estimated that the historic area of pinelands and hammocks in Dade County, exclusive of Everglades National Park, was originally about 152,000 acres (61,512.5 hectares). In 1975 these forests were reduced to about 8,000 acres (3,237.5 hectares), but only 5,000 acres (2,023.4 hectares) were sufficiently contiguious to provide viable habitat for native pine rockland plants.

By 1978 viable habitat had decreased to 4,500 acres (1,821 hectares), with only 1,700 acres (688 hectares) remaining in pristine condition; the rest was degraded by suppression of fire or by invasion of woody or exotic plants. Fire control in this area has resulted in an increase of tropical hardwood hammock vegetation, characterized by oaks, gumbo-limbo, strangler fig, poisonwood, and wild tamarind.

Conservation and Recovery

Controlled burning at three-to ten-year intervals may be necessary to maintain the pine rockland community; without fire the hammock will assume domination in about 25 years.

The lead-plant's habitat has been highly fragmented, and the smaller populations are not expected to survive. County officials are aware of the population in Bird Drive Park but are not actively managing the habitat. Without intervention, this site, too, will probably not survive.

Contacts

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

References

Shaw, C. 1975. "The Pine and Hammock Forestlands of Dade County." Report to Dade County, Florida, County Manager.

U.S. Fish and Wildlife Service. 1988." Recovery Plan for Five Florida Pine Rockland Species." Atlanta. 18 pp.

Ward, D.B. 1979. Rare and Endangered Biota of Florida; Vol. 5, Plants. University Presses of Florida, Gainesville.