As an homosporous fern, Ceratopteris has two independent, autotrophic phases: a developmentally simple haploid gametophyte and a vascular diploid sporophyte. The gametophyte phase, which develops after germination of the single-celled spore, can be cultured axenically on a simple inorganic nutrient medium. Development of this haploid phase is very rapid. Germination occurs at three days from inoculation and full sexual maturity is attained within six days from germination.. At maturity, the gametophyte consists of a small (<2 mm), simple two dimensional thallus with rhizoids, vegetative cells and sexual organs (archegonia and antheridia). Sexual differentiation is under the control of a pheromone, A_Ce (biosynthetically related to GA) and two sexual types exist. In the absence of A_Ce, gametophytes develop initially as females with archegonia and subsequently as hermaphrodites with both archegonia and antheridia. A meristem region is present and growth is indeterminate until fertilization of an egg occurs via swimming sperm that are released from antheridia in the presence of water. In contrast to females/hermaphrodites, gametophytes developing in the presence of Ace develop into small, determinate males that lack a meristem and produce large numbers of antheridia. The vascular sporophyte stage consists of 5 - 20 cm plants composed of a short upright stem (rhizome) with roots and leaves. In contrast to many ferns, the Ceratopteris sporophyte is not woody and grows rapidly as an annual. Spore production via meiosis occurs within sporangia that are located on the margins of fertile leaves. Upon maturity spore production is continuous and unlimited in number. Because individual haploid gametophytes can be self-fertilized, sporophytes completely homozygous across all genetic loci can be produced in one generation of selfing. Such sporophytes produce an unlimited number of genetically identical spores. Spores remain viable for many years and can be stored at room temperature. Further details about the life cycle and culture of Ceratopteris can be found in the Ceratopteris Bibliography (e.g., Hickok, Warne and Slocum, 1987; Hickok, Warne and Fribourg, 1995).