Rare and Unusual Aquatic Sedge is Invasive in Florida

by Colette Jacono, US Geological Survey; E-mail: colette_jacono@usgs.gov

Heavy growth of Scleria lacustris covers several hectares in water 40 cm deep. Many additional colonies are scattered in the distance.

What could be unusual about another invasive plant in Florida? Our most southern and species-rich state has surely received an overly generous share of "out-of-place" plants. In fact, Scleria lacustris C. Wright, more simply called Wright's Nut-rush, is strikingly unusual in many respects.

As a sedge (family Cyperaceae) it is atypical in existing as an annual species, truly aquatic in nature. The juvenile plants are well adapted to water influx during the summer growing season, developing thick, spongy stems and rooting at the nodes when submersed. The fibrous, floating roots help support the upright growth of plants until maturity and later the lodging that ensues across standing water in late season.

Scleria lacustris is extraordinary for its large size and robust stature. Where late season water levels reach 30 cm, single stemmed plants can grow to over two meters long while the stems expand to a hefty thickness of 2.5 cm. Plants develop multiple culms and a smaller stature; yet mature equally well where water has withdrawn in autumn.

Scleria lacustris is exceptional not only for its singular beauty but for its beastly touch. Silica impregnated prickles along the stem and leaves impart a deep slicing wound when handled. And finally, Scleria lacustris is rarely found in its native range, which extends across the tropics of Africa and America.

What may not be unusual about Scleria lacustris is the time lag, in this case twelve years, that has elapsed between early collections and the first troubling populations in Florida. Researchers acquainted with the task of reviewing herbarium specimens to analyze invasion processes typically find similar initial lag patterns in distribution.

Emergent with maidencane (Panicum hemitomon) and Eleocharis spp. in 30 cm of water, Scleria lacustris exceeds a height of 1.5 m.

In conservation marshes of central Florida, Scleria lacustris has demonstrated the ability to disperse rapidly and to develop into dense colonies. Open marshes subjected to hydroperiod fluctuations appear especially vulnerable. It is suspected that ducks and airboats may disperse the shining white nutlets. Nutlets may also float through drainage systems, leaving vast open water marshes, including the Everglades, at risk.

Recognize Scleria lacustris by its wide (~2 cm) pleated leaves, thick, three-angled stem streaked in red, and upright branching inflorescences full of large (to 4 x 2.5 mm), whitish shining nutlets.

Full results of findings are in press: Jacono, C.C. 2001. Scleria lacustris (Cyperaceae), an aquatic and wetland sedge introduced to Florida. Sida, Contributions to Botany 19(4). If you know of this plant, either in or out of its native place, please contact:
Colette Jacono, U.S. Geological Survey, 7920 NW 71st St., Gainesville, Fl 32653; (352) 378-8181 X 315; colette_jacono@usgs.gov

Go to the new USGS website about Scleria lacustris which includes detailed ID information, a distribution map and a downloadable flyer: http://www.fcsc.usgs.gov/Nonindigenous_Species/Scleria_lacustris/scleria_lacustris.html

See more Scleria lacustris pictures here.