Byrsonima lucida (Mill.) DC is the only member of the tropical plant family Malpighiaceae native to North America, and is considered a threatened species by the state of Florida. In order to better conserve the remaining natural populations of B. lucida, we studied the breeding system of this species in natural and garden settings. We carried out floral biology and breeding system experiments over three flowering seasons from 2009–2012. We found that stigmas were receptive mostly during the first 2 d of flowering, but not in the final day. Self-pollination yielded few fruits and pollinator exclusion yielded no fruit set, indicating self-incompatibility and pollinator dependence in this species. Obligate outcrossing and complete dependence on a specialist bee pollinator make B. lucida's small, fragmented populations vulnerable to extinction. Conservation measures should include protecting its specialized bee pollinator.