ANALYSIS OF DEVELOPMENTAL PREFORMATION IN THE ALPINE HERB CALTHA-LEPTOSEPALA (RANUNCULACEAE)

Developmental preformation is ubiquitous among alpine and arctic tundr a plant species and may cause a delay in plant morphological responses to environmental variation. The duration of preformation and seasonal pattern of development were examined in Caltha leptosepala to identif y characteristics of architecture and development that may influence t he timing of plant responses to environmental cues, both within a sing le growing season and between years. All structures in C. leptosepala are preformed: leaves are initiated one or two growing seasons before they mature and flowers are initiated one growing season before matura tion. Features of development and architecture in C. leptosepala, howe ver, appear to differ from the determinate growth patterns of other ex clusively performing species, and may allow within-season variability in the seasonal development and maturation of structures. Cohorts of l eaves initiated are asynchronous with maturation cohorts, and each yea r the number of leaf primordia per plant at snowmelt exceeds the numbe r to mature aboveground. Therefore, some flexibility in whether leaves complete a 2-yr or 3-yr developmental trajectory might occur. Plastic ity in reproductive phenotype might also occur via the process of flor al abortion. Despite developmental characteristics that might facilita te the expression of phenotypic plasticity, only slight variability wa s observed in the duration of preformation or in the seasonal pattern of initiation and emergence of structures. Growth patterns of C. lepto sepala thus appear to be fundamentally constrained, and limitations to annual growth may assure that sufficient preformed primordia remain b elowground at the end of each growing season for maturation of a full cohort during the subsequent season.