1	Fronds nutshell-like, upper surface flattened, 0.5−1 × as deep as wide, a small portion not flattened and with minute central papillae, fronds brownish punctate above (best seen in dead fronds), cells of fronds inflated in the lower portions and becoming progressively smaller and more compact toward the upper surface	Wolffia brasiliensis Fig. 209
–	Fronds globoid to ovoid, upper surface convex, 1−1.5 × as deep as wide, a small portion slightly flattened and roughened with minute central papillae, fronds not brownish punctate above, cells of frond uniformly inflated throughout	Wolffia columbiana

Key adapted from Weakley (2012).

Note: The first author did not encountered taxa within this genus in the field; however, the Carolina Vegetation Survey reported “Wolffia spp.” from the southwest side of Lake Waccamaw. Although a species-level identification has not been made, a key to the two species most likely to inhabit this location is provided below.