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SynopsisAutecology of pteridophytes may be refined by defining the plant community and habitat, and phytogeographic occurrence, of the species studied. Work with Blechnum spicant in the Pacific Northwest, and with Lorinserea areolata in the Southeastern U.S.A. has uncovered autecological differences for these species across habitats differing in overstory and hydrology. Natural history observations are necessary to suggest the most appropriate hypotheses to investigate objectively. A modification of Daubenmire's Canopy-Coverage method provides a grid across which many factors may be recorded or tested in repeatable objective manner. Such an analysis was used to test the association between L. areolata life-history classes and hummocks in hardwood swamps. Contingency tables were used to disprove the null hypothesis that L. areolata was distributed randomly with regard to hummocks. Hummocks were thus ‘safe sites’ for the completion of the life-cycle of L. areolata, and additional considerations of safe sites for Lygodium japonicum and Dryopteris ludoviciana are introduced. Analysis of biomass and coverage of Onoclea sensibilis where it is very abundant suggests that it is highly susceptible to competition where it shares plots with L. areolata. The concept of the optimum habitat with regard to abundance of the taxon, frequency of the habitat-type, successful reproduction, and susceptibility to competition between similar life forms is discussed.

Early gametophyte ontogeny was quantitatively distinct for Olympic Peninsula, Alaskan, and disjunct Idaho populations of the homosporous fern Blechnum spicant (L.) J. Sm. Although variable, gametophyte sex expression was shown to have a genetic component. Statistically different patterns of sex expression characterize each population. The Olympic Peninsula populations were distinct from each other but consistent in having a predominantly unisexual pattern. The disjunct Idaho population was predominantly bisexual at the time when comparable field collected gametophytes bear sporophytes. Preliminary experiments suggest that an antheridogen operates in this species. Increased sowing density favors maleness, and an extract from soil cultures of gametophytes shifts cultures to an exclusively male pattern after a dramatic suppression of growth. Mating experiments revealed that all populations are interfertile, although fertility was highest when the test Idaho population underwent intergametophytic‐selfing. The Idaho population evidenced a low level of genetic load consistent with predictions based on its sex expression. Although Olympic Peninsula populations evidenced apparent high genetic load in some experiments, failure to produce abundant sporophytes in other experiments suggested that additional cultural factors operated to reduce sporophyte formation. Moderate density mating experiments produced single sporophytes that were comparable to field collections. Isolated gametophytes underwent polyembryony after a time delay and gametophyte proliferation. Cultural conditions which allow sporophyte formation on isolated gametophytes without this delay or proliferation must be sought before further genetic analysis is undertaken.

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