Amaranthus pumilus, a federally threatened species that inhabits the transient and highly variable barrier beach environment of the United States, has been extirpated from nearly three-fourths of its historic range. This study ascertained habitat requirements and determined how certain biotic and abiotic factors influence A. pumilus | populations on Figure Eight Island, North Carolina. Data obtained were then compared to findings of Cakile edentula studies (C. edentula is common throughout the range of A. pumilus) in an effort to explain differences in range and abundance. Scarification and temperatures of 35?C enhanced seed germination. The majority of A. pumilus plants were found on overwash fans. Mortality was greatest following storm periods that inundated seedlings through four tidal cycles. Density of seedlings had no affect on mortality rate. No evidence was found for biological control of A. pumilus populations. Maximum seedling emergence from burial by sand was less than 1 cm. Amaranthus pumilus populations on Figure Eight Island appeared to be physically rather than biologically controlled. Characteristics such as a shorter growing season and inability to emerge from depths greater than 1 cm may be adaptive disadvantages when compared with C. edentula.