Seed banks of Aeschynomene virginica may have significant implications for population dynamics and conservation of this rare, freshwater wetland, annual plant. Little work, however, has been done on the size and extent of the seed bank of this threatened plant. Experimental seed banks were placed at three sites to estimate overwinter seed survivorship and the potential for long-term seed dormancy. The soil beneath 5 extant populations was sampled after current-year seed germination and before seed fall to determine the presence and spatial distribution of seeds surviving more than one season. An average of 47.4 ± 2.8 (± 1 SE) of the 125 seeds placed in the field survived over winter. Of those seeds that were recovered from experimental seed banks, an average of 37.3 ± 1.7 germinated under greenhouse conditions. When the seed coats of ungerminated seeds recovered from experimental seed banks (10.3 ± 0.3) were scored, 4.9 ± 0.8 seeds germinated. Analysis of soil cores from the field showed high variability in natural seed distribution. Significantly more potentially viable seeds were found in plots with standing A. virginica plants than in those with no standing plants. Results indicate that A. virginica forms a Type III seed bank. The seeds in a seed bank may augment population size following poor seed production years, or they may reestablish locally extinct A. virginica populations.