Preformation, architectural complexity, and developmental flexibility in Acomastylis rossii (Rosaceae).

The duration of preformation and the seasonal pattern of development were studied in the architecturally complex alpine perennial Acomastylis rossii. Each leaf and inflorescence requires 3 yr to progress from initiation through structural and functional maturity to senescence. As a consequence, three cohorts of preformed organs, initiated in successive years, are borne simultaneously by each individual plant. The oldest cohort matures immediately following snowmelt, after which no additional leaves are matured until the following spring. A second cohort remains below ground in the apical bud and continues development, while a third cohort is initiated. Initiation and development of primordia proceed below ground throughout the summer and continue for at least 2.5 mo after aboveground structures have senesced. Acomastylis rossii maintains numerous dormant vegetative buds containing preformed leaf primordia in the axils of senesced leaves. Developmental preformation has been widely reported in arctic and alpine tundra environments and has been theorized to severely constrain rapid responses to environmental variation. The presence of many such preformed structures may mitigate some of the constraint on plant response to environmental variation imposed by the long developmental trajectories of leaves and inflorescences in apical buds.