The majority of homosporous ferns are characterized by a life-cycle which permits the production of a genetically homozygous zygote following selffertilization of a single gametophyte (intragametophytic selfing). This homozygosity leads to the expression of recessive deleterious or lethal genes (genetic load, as defined here) present in the genotype, unless this expression is buffered by the polyploid system. Sporophytes expressing such genes will be eliminated rapidly and the spore genotypes produced individually by the remaining viable sporophytes will be genetically uniform, barring mutation and meiotic irregularities (e.g., homeologous pairing; Klekowski, 1979). In species which regularly undergo selfing, genetic load will be absent or will be expressed at low levels (Klekowski, 1979). Thus, analysis of genotypes for genetic load allows for an estimate of the genetic variability in a population. The fern life-cycle also permits reproduction which is genetically analogous to inbreeding and outbreeding in angiosperms, the latter facilitating the storage of recessive deleterious and lethal genes (Wallace, 1970). Although none of the above patterns of reproduction are mutually exclusive, work of the past decade has led to the hypothesis that specific morphological and developmental features of the gametophyte generation will increase the probability of selfing or crossing (intergametophytic mating) and that these probabilities can be correlated with estimates of heterozygosity in the form of genetic load (Lloyd, 1974). However, more recent work with Ceratopteris (Lloyd & Warne, 1978) and Acrostichum (Lloyd & Gregg, 1975) suggests that the past hypotheses are insufficient to explain the genetic diversity expressed in these species and that other factors are involved. This paper summarizes our most recent work on the gametophyte morphology, reproductive biology, and genetic diversity in a number of populations of Acrostichum aureum distributed from Florida to the northern coast of South America and attempts to circumscribe the current problems in this field. The genus Acrostichum consists of at least three species: A. danaeifolium Langsd. & Fisch., a New World endemic which is widely distributed in fresh water and slightly saline swamps (Adams & Tomlinson, 1979); A. aureum L., circumtropical in distribution and usually most abundant in mangrove habitats where it can withstand partial tidal immersion (Holttum, 1954; Small, 1938); and A. speciosum Willd., a species of tropical Asia and Australia which is abundant in mangroves through Malaya in areas frequently inundated by tides (Holttum, 1954). These types of habitats are extreme; few species of plants have evolved the necessary physiological and morphological features to successfully colonize them. Previous work on the gametophyte generation in Acrostichum includes mor-