Oenothera riparia Nutt. (ONAGRACEAE) – Charleston and Colleton Counties: In the drawdown zone on both the Charleston and Colleton County sides of the Edisto River near Jacksonboro, South Carolina, dozens of plants were observed growing primarily around stumps and on logs adjacent to both freshwater tidal swamp forests and freshwater tidal marshes along a 12 km stretch of river. Nearby swamp forest species overhanging the O. riparia plants frequently included Acer rubrum L., Liquidambar styraciflua L., Morella cerifera (L.) Small, Platanus occidentalis L., Taxodium distichum (L.) Rich., and Viburnum nudum L. Oenothera riparia was also observed growing adjacent to former rice impoundments composed of freshwater tidal marshes dominated by Pontederia cordata L., Sagittaria lancifolia L., Spartina cynosuroides (L.) Roth, and Zizania aquatica L. Native vines, Apios americana Medik. and Clematis crispa L., co-occurred with O. riparia along the banks of the Edisto River adjacent to both swamp forest and marsh habitats. Specimens of this O. riparia population were vouchered at The Citadel Herbarium (CITA), 32845052.4200N, 80826048.4400W, 8 July 2016, J.M. Gramling s.n. (CITA-2455, CITA-2456, & CITA- 2457) and later collected by Daniel Castillo s.n. at the same site, 13 June 2017 (USCH).
Commonly called the riverbank evening primrose, O. riparia is a southeastern Coastal Plain endemic known from the Cape Fear andWaccamaw River systems in North and South Carolina and in southeastern Virginia from the Northwest and North Landing Rivers. In South Carolina, this species was previously known to occur only in the Waccamaw River Basin and has been collected from the banks of the Waccamaw, Greater Pee Dee, and Black Rivers in that basin system (Weakley 2015). The Black River in Georgetown County was previously considered the southernmost occurrence of O. riparia. The Edisto River population represents two new county records and extends the southern limit of this taxon by roughly 120 km to the southwest. NatureServe has it ranked as a G2– Globally Imperiled to G3–Globally Vulnerable taxon, but no state rank has been assigned (NatureServe 2017). We would recommend that O. riparia be listed as S2–Imperiled in South Carolina, indicating that this plant is likely made up of fewer than 20 populations statewide.