Fern life history and reproductive biology of 14 species was investigated from 1973-1978 at Woodman Hollow State Preserve, a small, isolated mesic canyon in central Iowa. A microclimate study was conducted to characterize the local diversity of microhabitats and to assess the likelihood that the canyon is a topographically controlled refuge for mesic species. A bryofloristic analysis was conducted to establish whether the canyon was and has continued to be a refuge for mesic species until the present. A phytogeographic analysis of the pteridophyte flora was conducted to assess whether the study species were peripheral, disjunct, or possibly relictual in their occurrence at Woodman Hollow. Observations were made on a quantitative basis throughout the year on each stage of the life cycle of each species. Aspects studied included the distribution, abundance, and foliar phenology of sporophytes, the production, release, dispersal, and germination of spores, the occurrence, demographics, mortality, sexuality, and periodicity of gametophytes, and the production, mortality, and maturation of sporelings. Environmental factors (physical, chemical, biotic) were identified which promoted or prevented the completion of the sexual cycle. Efforts were made to discern species specific (intrinsic) attributes from environmental (extrinsic) influences. Experimental investigations were conducted in the field and laboratory to verify observations. The character of vegetative reproduction was contrasted with sexual reproduction;The study species included three species which annually form sporeling plants (Adiantum pedatum, Cystopteris fragilis var. mackayi, and Woodsia obtusa), three species which infrequently form sporelings (Botrychium virginianum, Dryopteris goldiana, and Dryopteris spinulosa), and eight species which did not produce gametophytes or sporelings during the study (Athyrium angustum, Camptosorus rhizophyllus, Cryptogramma stelleri, Cystopteris bulbifera, Cystopteris protrusa, Matteuccia struthiopteris, Osmunda claytoniana, and Polypodium virginianum);Six aspects were identified at Woodman Hollow as significant to the biology of fern sexual reproduction and its comprehension. These aspects are (1) physical structure and complexity of the study area, (2) phytogeography of the study species, (3) differential reproductive capacity and capability of the study species, (4) importance of timing and extent of substrate disturbance, stability, and moisture, (5) variability of gametophyte breeding system through time (in nature), and (6) separation of plants which complete the sexual cycle (effective reproduction) from plants which do not (reproductive noise).