As part of an investigation of the extent of habitat-specific variation in Thuja occidentalis L., cones were collected from cliff (dry upland) and swamp (wet lowland) sites in southern Ontario. The number of seeds per cone, number of fully developed seeds per cone, seed fresh weight, length, and width, length and width of embryo area, and length and width of right wing were determined. Seed yield on a per cone basis did not vary between habitat types or among sites within habitats. There was, however, significant variation among trees within sites. Individual seed characters did not vary between habitat types, but significant variation existed among sites within habitats, among trees within sites, and among cones within trees. Only the width of right wing failed to show cone to cone variation within individual trees. The majority of explainable variance for all characters could be apportioned to trees within sites. This and a relatively low degree of cone to cone variation suggest that the seed morphological characters were under strong maternal control. Differences among sites are thought to be the result of local environmental variation rather than genetic differences. The lack of habitat-specific seed character variation indicates that contrasting moisture regimes have little effect on quantitative seed morphology. No evidence exists for ecotypic variation with respect to seed morphology. Key words: Thuja occidentalis, eastern white cedar, seed morphology, ecotypes, cliff, swamp.
