AN ANNOTATED CHECKLIST OF THE VASCULAR FLORA OF WASHINGTON COUNTY, MISSISSIPPI 1 Charles T. Bryson Daniel A. Skojac, Jr. USDA, ARS USDA, FS, Southern Region Crop Production Systems Research Unit Chattahoochee NF Stoneville, Mississippi 38776, U.S.A. 3941 Highway 76 Chatsworth, Georgia 30705, U.S.A. ABSTRACT Field explorations have yielded 271 species new to Washington County, Mississippi and Calandrinia ciliata (Ruiz & Pav.) DC. and Ruellia nudiflora (Engelm. & .A. Gray) Urban new to the state. An annotated list of 809 taxa for Washington County is provided and excludes 59 species that were reported from counties adjacent and included in the 1980 Washington County and environs flora, but have yet to be docu- mented from Washington County. RESUMEN Exploraciones de campo han dado como resultado 271 especies nuevas para Washington County, Mississippi y Calandrinia ciliata (Ruiz & Pav.) DC. y Ruellia nudiflora (Engelm. & .A. Gray) Urban nuevas para el estado. Se aporta una lista anotada de 809 taxa para Washington County y se excluyen 59 especies que estaban citadas de condados adyacentes e incluidas en la flora de 1980 de Washington County y alre- dedores, pero que no se han documentado aún para Washington County. INTRODUCTION The flora of Mississippi, especially the Yazoo-Mississippi River Alluvial Plain, is poorly reported (Bryson & Carter 1994; Skojac et al. 2007) compared to other physiographic regions of Mississippi and of adjacent states. Lowe’s Plants of Mississippi (1921) still remains the only effort at a comprehensive flora of the state. Several county floras have been compiled, mostly by graduate students at various universities; however, comprehen- sive floras are lacking for more than 80% of Mississippi’s 82 counties. Gunn et al. (1980) prepared a Flora of Washington County and Environs. This work has been the standard for plant identification by researchers, consultants, educators, farmers, and the general public for the past quarter century. Gunn et al. (1980) listed 669 taxa for Washington County and environs; however, 131 species were collected in the adjacent counties of Bolivar, Humphreys, Issaquena, Sharkey, and Sunflower. Because supplies of Gunn et al. (1980) were depleted almost a decade ago and collection efforts have yielded additional species to the county, our objective is to provide an updated list of the species found only within the confines of Washington County, Mississippi. Washington County is in the Mississippi-Yazoo alluvial plain of the physiographic or land use area known as the Delta Region (Lowe 1921). The county is bordered by the Mississippi River on the west and lies about half way between Memphis, TN and Vicksburg, MS (Lowe 1921; Skojac et al. 2007). The county is about 20,000 ha and the elevation ranges from 27.5 to 43 m above sea level. Thus, the topography of the region is relatively flat except along the natural and man-made levees of creeks, streams, oxbow lakes, and the Mississippi River. Little of the county remains undisturbed. Most of the land was cleared for row crop production, espe- cially the well-drained areas, and many areas have been under cultivation since the mid 19th century. Soils of Washington County are deep and fertile and of alluvial origin, and range from poorly drained fine clays to well drained silt loams and sands (Morris 1961). The five main soil associations found in Washington County are nearly level and range from poorly, moderately, and excessively drained. These soil associations occur in areas that are classified as alluvial, slack-water, low terraces, old natural levees and recent natural le- vees. Over one third of the soils in the county are highly productive sandy loams (e.g., Dundee & Bosket soils) 1Formerly at USDA, FS, Southern Research Station, Center for Bottomland Hardwoods Research, Stoneville, MS 38776. J. Bot. Res. Inst. Texas 5(2): 855 – 866. 2011 856 Journal of the Botanical Research Institute of Texas 5(2) and have been historically used for cotton production. Recently, the crop diversity on these soils includes corn, cotton, and soybean, while silt and clay soils are primarily utilized for rice and soybean production, farm raised catfish ponds, or scattered remnant forests. The native mixed deciduous bottomland forest is a product of edaphic rather than climatic conditions (Gunn 1980). The climate of Washington County is considered temperate with average temperatures ranging from 8°C in January to 24°C in July. The summers are hot and humid with daytime temperatures occasionally over 38°C. During short cold periods in the winter, temperatures are rarely below -10°C. The average growing season is about 200 days with an average killing frost on November 2 and the last hard freeze usually occurs in early to mid March. Vouchers for the additions to the Washington County flora are deposited in herbaria at the USDA-ARS Jamie Whitten Delta States Research Center (SWSL) and the USDA Southern Hardwoods Research Laboratory (CBHRL) both at Stoneville, MS as indicated in Table 1. Duplicates of many of these collections were distrib- uted to other herbaria within Mississippi (DSC, IBE, MISS, MISSA, MMNS, or USMS) and elsewhere depend- ing on the number of duplicates. Collector, collection number, and herbarium or a publication that reported additional species to Washington County are cited following each species added since Gunn et al. (1980). RESULTS AND DISCUSSION As a result of fieldwork during the past three decades, 271 species have been added to the flora of Washington County, Mississippi. Calandrinia ciliata (Ruiz & Pav.) DC. and Ruellia nudiflora (Engelm. & A. Gray) Urban, both new to the state, are reported in the annotated flora of Washington County (Table 1). Since Gunn et al. (1980), 72 species listed from adjacent counties were collected within the county; 59 species have not been detected yet in Washington County and are listed in Table 2. A few species were misidentified (e.g., the vouch- er for Sida elliottii Torr. & A. Gray was an abberant specimen of S. rhombifolia L.), and thus not included in the annotated list for Washington County (Table 1) but retained in those species yet to be collected within the county (Table 2). Nomenclature changes since Gunn et al. (1980) were updated to follow published volumes of Flora of North America, e.g., Urochloa ramosa (L.) R.D. Webster for Brachiaria ramosa (L.) Stapf. Other taxa were redetermined or aligned with currently accepted nomenclature or where species concepts have changed, such as Carex aureolensis Steud. rather than C. frankii Kunth, now defined as taxa with a distribution well north of the Delta Region. Alignment of families not yet treated yet in Flora of North America follow Missouri Botanical Garden’s Tropicos (Tropicos 2011). Author abbreviations follow The International Plant Names Index (IPNI 2011). With these additions and realignments as mentioned above, 809 taxa are now known within the bounds of Washington County. Of the 117 Family cited as occuring in Washington County and environs by Gunn et al. (1980), one fam- ily, one family, Asclepiadaceae, was lumped into Apocynaceae (Table 1), and Melastomataceae, was excluded because no species within the family were found within the confines of Washington County (Table 2). Eleven families were added to the flora of Washington County and include Annonaceae, Berberidaceae, Dioscoreaceae, Cannabaceae, Fumariaceae, Haloragaceae, Hippocastanaceae, Lygodiaceae, Simaroubaceae, Sterculiaceae, and Thelypteridaceae (Table 1). Fumariaceae was included in Gunn et al. (based on a collection of Corydalis flavula (Raf.) DC. from an adjacent county and was included based on a recent collection. Other family names provided by Gunn et al. (1980) were changed to conform to new classification schemes, e.g., Dryopteridaceae for Asplidiaceae; Amaryllidaceae folded into Liliaceae; and Smilaceae segregated from Liliaceae. Ultimately, 122 plant families are listed for Washington County (Table 1). Additional field research should add native taxa to this list. Also, species not native to the Delta Region will undoubtedly be added because of human activities and the vast areas under cultivation. Bryson and Skojac, Flora of Washington Co., Mississippi 857 TABLE 1. Annotated list of the species collected within Washington County, Mississippi cited in Gunn et al. (1980) or confirmed as noted by literature citation or as new data (collector, collection number, and herbaria where vouchers are deposited). PTERIDOFITAS Bromeliaceae Tillandsia usneoides L. Aspleniaceae Asplenium platyneuron (L.) Britton, Sterns & Poggenb. Cannaceae Canna X generalis L. H. Bailey Azollaceae Azolla caroliniana Willd. Commelinaceae Commelina communis L. Dryopteridaceae Commelina diffusa Burm. f. Athyrium filix-femina (L.) Roth. var. asplenioides (Michx.) Hulten Commelina virginica L. Onoclea sensibilis L. Murdannia nudiflora (L.) Brenan (Bryson 23762) Equisetaceae Tradescantia ohiensis Raf. Equisetum hyemale L. Tradescantia virginiana L. Lygodiaceae Cyperaceae Lygodium japonicum (Thunb.) Sw. (Bryson 16767, SWSL) Carex abscondita Mack. (Carter et al. 1990) Carex albicans Willd. ex Spreng. (Carter et al. 1990, cited as C. phy- Marsileaceae sorhyncha Liebm. ex Steud.) Marsilea vestita Hook. & Grev. Carex annectens E.P. Bicknell Ophioglossaceae Carex blanda Dewey Botrychium virginianum (L.) Sw. (Skojac 454, CBHRL) Carex bromoides Schkuhr subsp. bromoides (Carter et al. 1990) Ophioglossum vulgatum L var. pycnostichum (Fernald) Love & Love Carex bulbostylis Mack. (Bryson 11522, SWSL)