Rediscovery of Marsilea vestita subsp. vestita in Pulaski County, Arkansas After 162 Years

We report first vouchered record of Marsilea vestita Hook, and Grev. subsp. vestita from Pulaski County Arkansas in 162 years. Two patches of hairy water fern, M. vestita subsp. vestita were discovered by W. Shepherd on 20 September 1997 at edge of a backwater pond along Arkansas River at Murray Park in Little Rock. Prior to this record, most recent collection of this species from Pulaski County was taken from the margin ofsmall swamps in deep bottom woods on Arkansas River, not far below Little inJuly of 1835 by German botanist and physician George Engelmann. Witsell visited Shepherd's site to make collections on 24 September 1997 and again on 9 October 1997 withJ.H. Peck to conduct a census and evaluate status of population. A total of 53 patches covering 124 m2 was discovered along shoreline of backwater ponds behind a series of five wingdamdredge-spoil islands created by Corps of Engineers' McClellan-Kerr Navigation Project. Voucher specimens are located in LRUherbarium at University of Arkansas at Little Rock [Shepherd 452 (LRU), Witsell 18 (LRU)]. Marsilea vestita subsp. vestita occurs over western U.S., but is most abundant in central Great Plains region (Johnson, Systematics of new world species of Marsilea (Marsileaceae). Vol. 11. Systematic Botany Monographs. University of Michigan at Ann Arbor. 1986). Arkansas populations are at eastern edge of species's range and are rare enough for species to be on Arkansas Natural Heritage Commission's special plant list of rare and sensitive species. Other occurrences of Marsilea vestita subsp. vestita in Arkansas have been recorded in Arkansas, Ashley, Bradley, Chicot, Crawford, Desha, and Faulkner counties as Marsilea mucronata A.Braun, M. uncinata A. Braun and M. vestita var. uncinata (A.Braun) Baker (Peck, J. and C. Taylor. Checklist and distribution of Arkansas Pteridophytes. Proc. Arkansas Acad. Sci. 49:130-137, 1995). There is great genetic and environmental variability in genus Marsilea and taxa are often difficult to determine in absence of more taxonomically reliable sporocarps. However, relative development of roots and lateral shoots, degree of development of lateral shoots, and leaflet shapes are of some value to distinguishing taxa (Johnson, Systematics of new world species ofMarsilea (Marsileaceae). Vol. 11. Systematic Botany Monographs. University of Michigan at Ann Arbor. 1986). Since no sporocarps were present in these Pulaski County populations, we had to rely on vegetative characters inmaking our identification. Plants exhibiting two distinct growth forms were found during all three visits to site: a short form growing on sandy-to-muddy substrate at edge of water with some plants entirely submerged and a taller form found on bank above water level. Heterophylly inamphibious plants is not uncommon and is exhibited inMarsilea by phenotypic plasticity of leaves resulting in distinct floating, submerged, or aerial (land) leaves (Johnson, Systematics of new world species of Marsilea (Marsileaceae). Vol. 11. Systematic Botany Monographs. University of Michigan at Ann Arbor. 1986). Johnson (1986) reported that land leaves are smaller than aquatic leaves, though opposite was observed at this site. The plants with largest leaves, in excess of 20 cm tall, were found growing on dry land behind a partially submerged logalong edge of water. The taller terrestrial plants had fewer leaves than smaller aquatic ones. Patch size ranged from isolated individual plants to dense clusters up to 20 m long and 3 m wide. 56.6% of patches covered less than 1 m2,24.5% covered from 1 to 5 m2,13.2% covered from 5 to 10 m2,and 5.7% covered from 10 to 20 m2.A typical patch was shoreline linear, extending less than 1 m into water but often twice as far onto shore, depending on slope of bank. The area of greatest density fell within 0.5 m of shore ineither direction, with plants farthest from water's edge being fewer and more widely spaced. Patches on more steeply sloping banks were restricted to shoreline more than patches on less steeply sloping banks. Marsilea was absent from flat areas along shoreline, possibly excluded by abundant grasses. The plants were concentrated on calm banks of backwater ponds and gentle, meandering streams connecting these ponds to river.Only one small patch of plants was found on more turbulent river-side of islands, and itwas approximately 2.5 m up bank from waters edge. Associated genera were Pluchea, Rotala, Polygonum, Sagittaria, and several grasses. Acknowledgments. — The authors would like to thank Dr.James H. Peck and Harriet Jansma for their help in this research.