|Listed||October 28, 1992|
|Description||Small, grasslike aquatic herb with rounded, hollow numerous leaves.|
|Habitat||Small to medium-sized shallow, clear streams through riparian forests.|
|Threats||Clearcutting of streambank timber, canopy removal.|
The Isoetes louisianensis Louisiana quillwort is a small, grasslike aquatic herb in the quillwort family. Louisiana quillwort is a seedless vascular plant that reproduces by spores and is closely related to ferns. The species' slender quill-like leaves arise from a short fleshy stem or corm that is shallowly rooted in the substrate. The leaves are rounded, hollow and swollen at their base. Leaves are numerous, varying in length from 6-16 in (15-40 cm) depending on water depth. The sporangia, or spore-containing structures, are embedded in the broadened bases of the leaves. The species is heterosporous, producing both megasporangia and microsporangia. The species is characterized by its born-spotted sporangial walls and megaspores with high reticulate ridges producing a spiny effect. Louisiana quillwort has been reported to sporulate twice a year, producing megaspores in the spring and microspores in the fall.
This semi-aquatic plant is known from three locations in Louisiana. The streams in which the species is found are typically small to medium sized, shallow and with clear, tannin-colored water, running through narrow riparian forest communities. Preferred substrates are stable mixtures of silt, sand, and gravel. Louisiana quillwort occurs predominately on sand and gravel bars on accreting sides of streams and in moist over-flow channels. The species is found less commonly on low sloping banks near, and occasionally below, the low water level. Individuals are regularly inundated as much as 20 in (50 cm) of water following rains, and may be inundated for long periods in wet seasons. Corm depth has been found as great as 1.2 in (3 cm), indicating a tolerance for some deposition of materials. The species may be found singly or in numbers of several hundred.
Louisiana quillwort is known to exist in three locations in Washington and St. Tammany Parishes in Louisiana. The largest two populations contain several hundred individuals each; the smallest contains only four immature individuals. It is possible the species was once more widespread, but there is no concrete evidence to support this. The most extensive population occurs in portions of Thigpen and Clearwater Creeks. Four individuals are known from the Mill Creek area. A population in the Little Bogue Falaya Creek contains several hundred individuals.
The primary threats to Louisiana quillwort are activities that would affect the hydrology or stability of the streams in which it occurs. The species has been eliminated from one location by construction activities and canopy removal. It has been affected in another portion of this area by changes in vegetation composition due to clearcutting of stream-bank timber and flow diversion.
All known stream habitat supporting this species is associated with a well-developed stream canopy. Canopy removal alters the light regime under which the species is currently known to exist. Some streambank timber harvest have occurred at various locations along all streams supporting Louisiana quillwort. It is believed that these harvests have adversely affected the species. Stream-bank timber removal can also lead to an increase in surface runoff and contribute to stream erosion and/or siltation.
Sand and gravel mining along the species' range is affecting the hydrology, water quality, and substrate stability of that area. Portions of the area have been completely cleared, channelized or rerouted by sand and gravel mining activities. Headwaters into one area have been ditched to direct surface drainage away from the mining operation. Excessive algal growth and sediment pollution has occurred due to this alteration of the hydrologic regime. All of these factors threaten the existence of this species.
Conservation and Recovery
The recovery efforts of Louisiana quillwort include the following. Further searches for undiscovered individuals in similar habitats need to be conducted. Studies into the reproductive cycle and specific habitat requirements could lead to a better understanding of the species. This information could be used to develop a cultivation and seed bank program that could be used to reintroduce the species in appropriate habitat. Binding agreements with private landowners or possible land acquisition should be considered to protect the few remaining populations that occur on private land. Timber harvesting throughout the species' range should be carefully monitored to help keep the canopy intact. Further mining permits and water diversions throughout the species' range should be carefully considered so as not to further impact Louisiana quillwort.
Louisiana Natural Heritage Program
Louisiana Department of Wildlife and Fisheries
P.O. Box 98000 (70898)
2000 Quail Drive
Baton Rouge, Louisiana 70808
U. S. Fish and Wildlife Service
Ecological Services Field Office
825 Kaliste Saloom Road, Suite 102
Lafayette, Louisiana 70508-4231
Telephone: (337) 291-3100
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
U.S. Fish and Wildlife Service. 28 October 1992. "Endangered and Threatened Wildlife and Plants: Determination of Endangered Status for the Plant Isoetes louisianensis (Louisiana Quillwort)." Federal Register 57: 48741-48746.