Heterocarpy was studied in Cakile edentula var. edentula (Brassicaceae) populations from Michigan and North Carolina. C. edentula var. edentula produces a fruit that is transversely divided into two morphologically distinct proximal and distal segments. Seeds from the distal fruit segment and seeds from the North Carolina population were significantly heavier than seeds from the proximal fruit segment or Michigan, respectively. Both fruit segments typically produced one seed; however, double seed set and failed seed set were most prevalent in the proximal fruit segment from the Michigan Morphological differences between proximal and distal fruit segments were found to affect wind and water dispersal. During the wind tunnel observations, distal segments traveled in a straight line or broad arc; whereas, the proximal segments exhibited circular rotation without moving away from the wind source. Distal fruit segments stayed afloat in salt water significantly longer than did the proximal segments. Flotation time for proximal and distal segments was statistically equal in freshwater but significantly less than either of the salt water treatments. Germination dimorhpisms were found between seeds from Michigan and North Carolina but not between proximal and distal seeds. Physical barriers provided by the fruit and seed coat equally inhibited germination in the proximal and distal seeds. Neither proximal nor distal seeds were influenced by cold stratification. Though heavy seeds had a greater percent emergence, the heavier distal seeds emerged at the same rate as the light-weight proximal seeds. Differences between seeds from Michigan and North Carolina may involve a population genetic component or variable conditions under which the seeds matured, as opposed to seed mass. Strong environmental selection for particular seed morphs was observed between populations and between microsites in populations. Thus, the most important factor controlling seedling establishment may not be the inherent germination potential of a seed, rather the habitat in which the seed is found.