Schoenoplectus hallii, S. saximontanus, and the Putative S. hallii X S. saximontanus Hybrid: Observations from the Wichita Mountains Wildlife Refuge and the Fort Sill Military Reservation 2002 - 2010

Schoenoplectus hallii, S. saximontanus, and the putative S. hallii × S. saximontanus hybrid are obligate wetland sedges that occur in the sparsely vegetated margins of ponds, ditches or swales with fluctuating water levels. The species are amphicarpic and have easily identified differences between spikelet and basal achenes. We surveyed selected sites at the refuge in 2001, 2002, and 2007 – 2010, surveyed 4 sites on the Fort Sill Military Reservation in 2009 and 2010, and collected voucher specimens from all populations. Scanning Electron Microsope (SEM) photographs of spikelet and basal achenes indicate distinct morphological differences between species and the presence of “winged” ridges on S. saximontanus. Field observations indicated that populations at all sites vary in size and species distribution annually, and that both parental species appeared to be declining in number. We concluded that in populations where S. hallii and S. saximontanus co-occur, hybridization may be a threat to one or both parental species. The distribution of achenes by waterfowl and ungulates indicates that management to prevent establishment of mixed populations, and therefore hybridization, is not practical. We recommend that S. hallii be evaluated for federal listing under the Endangered Species Act, a range-wide assessment be completed for S. saximontanus, and that all sites with mixed populations should be examined for the presence of hybrids.