Alabama Streak-sorus Fern

Thelypteris pilosa var. alabamensis

Description

The Alabama streak-sorus fern is a small evergreen with linear-lanceolate fronds 4-8 in (10.2-20.3 cm) long. The fronds appear clustered, arising from short, slender rhizomes covered with reddish-brown scales. The stipe portion of the frond (petiole) is slender, erect to ascending, 0.4-1 in (1.-2.5 cm) long, and covered with long hairs. The blade is typically 1-4 in (2.5-10.2 cm) long, and divided once into many ovate to suborbicular leaf segments (pinnae). The sori (groups of spore-producing reproductive structures) occur on the underside of the blades and are linear in shape. This is the only southeastern species of Thelypteris which lacks indusia (a thin membrane covering the sori).

Habitat

The species takes root in crevices or on rough rock surfaces of Pottsville sandstone along the Black Warrior River in Alabama. Plants typically occur on "ceilings" of sandstone overhangs (rockhouses), on ledges beneath overhangs, and on exposed cliff faces. These bluffs and overhangs are usually directly above the stream; however, some are located a short distance away from the river. Locations vary in slope aspect and shade coverage, from completely shaded to partially sunny on exposed bluff faces. The sites are kept moist by natural water seepage over the sandstone from up-slope runoff. Water vapor from the stream increases the humidity for those sites directly above the water or nearby.

The species grows among various bryophytes and is often associated with climbing hydrangea (Decumaria barbara ), Thalictrum clavatum, Heuchera parviflora, and the ferns Osmunda cinnamonea, O. regailis, and, most notably, the Appalachian bristle fern (Trichomanes boschianum ).

Distribution

The species' known range is confined to an approximately 3.25 mi (5.2 km) stretch along the Black Warrior River in Winston County, Alabama. Past distribution is thought to have been in this same general area.

Presently in this area, 15 separate localities have been documented. All sites are within the boundaries of the Bankhead National Forest and the majority occur on U.S. Forest Service land. Several localities are on private inholdings.

Threats

The type locality, which is approximately 5 mi (8 km) downstream of extant populations, was destroyed in 1960. The cliffs where the plants grew were leveled when a new bridge was constructed. The area was subsequently flooded with the completion of Lewis Smith Dam several miles downstream. The impoundment inundated suitable habitat, and perhaps plants, upstream and downstream of the type locality. Currently, plants are located on both sides of a highway bridge upstream of the reservoir's influence. Plants may have been destroyed by this bridge construction. Future road or dam construction along the upper reaches of the river poses a potential threat to extant populations.

Logging of woodlands above the occupied sites could adversely affect the microhabitat needed by the species. The species is dependent on up-slope runoff and seepage to maintain the substrate moisture. Heavy timbering or clear-cutting could alter the area's hydrology by interrupting this natural seepage. Additionally, the loss of the canopy would increase ambient light and lower the humidity. Thus, timber removal would dehydrate the habitat and such could be detrimental to this species.

Overhangs or rockhouses are habitat for about 50% of the known populations. These areas are frequented by hikers, fishermen, and campers and are subject to vandalism. Two of the larger populations occur in rockhouses which are often used by humans, as evidenced by numerous footprints, abundant litter, and old campfires. Intentional or incidental damage caused by hikers and campers, in addition to the heat and smoke from campfires, threatens these populations.

Over-collecting for any purpose would adversely impact this species due to its rarity and the small number of individuals at several sites. The species' limited distribution makes it vulnerable to collectors and vandals.

No species-specific diseases or predators have been identified. However, disease or predation could have a serious adverse impact on the small and fragmented populations.

The greatest threat to this species is its extreme vulnerability due to its limited range and small number of plants at many of the sites. A single natural or anthropogenic disturbance could seriously reduce the population size and affect the species' viability. Catastrophic flooding through the narrow gorge could possibly scour all the occupied sites to such a degree that the size of the population would be significantly reduced. Sites near the water have few individuals (one to three plants), probably because of scouring from seasonal (as opposed to catastrophic) flooding. Severe drought would decrease the substrate moisture and be detrimental to this species. A local drought in 1990 appeared to kill individual plants at several localities.

As a natural erosional process, sandstone overhangs and bluffs periodically erode small and large sections. A site could be completely eliminated (including one with a large number of plants) if one such incident occurred.

Conservation and Recovery

Federal involvement is expected to include the Environmental Protection Agency in consideration of the Clean Water Act's provision for pesticides registration, and waste management actions. The U.S. Army Corps of Engineers will include this species in project planning and operation and during the permit review process. The Federal Highway Administration will consider impacts of bridge and road construction at points where known habitat is crossed. Urban development within the drainage basin may involve the Farmers Home Administration and their loan programs.

Contacts

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

Daphne Ecological Services Field Office
P. O. Box 1190
Daphne, Alabama 36526-1190
Phone: (334) 441-5181
Fax: (334) 441-6222

Reference

U.S. Fish and Wildlife Service. 8 July 1992 "Endangered and Threatened Wildlife and Plants; Threatened Status for the Plant Thelypteris pilosa var. alabamensis (Alabama Streak-sorus fern)." Federal Register. 57(131): 30164-30168.