The breeding system of Laguncularia racemosa is variable among populations; some populations are androdioecious while other populations lack male plants. To determine whether androdioecy is widespread in L. racemosa, 65 populations were surveyed in Florida and the Bahamas. Fruits are water-dispersed, so the observed distribution of breeding systems was compared to local and regional water currents in order to determine whether dispersal could be important to the maintenance of male plants in androdioecious populations. Twenty-two of the 36 populations surveyed in Florida were androdioecious, with male frequencies that ranged from 1–68%. On the Florida east coast, all populations north of latitude 26°30′ N lacked males while all populations south of this latitude were androdioecious, which suggests that northern populations may lack males due to dispersal limitation. The pattern of distribution on the Florida west coast suggests that males may be maintained in some populations via dispersal. Nine islands in north-central Bahamas were surveyed, and androdioecious populations were found only on San Salvador Island, where male frequencies ranged from 5–28%. Dispersal, fragmentation, and selection hypotheses are suggested to explain the observed pattern of distribution; these hypotheses will be tested in future studies.
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