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Preformation, the initiation of organs one or more years prior to maturation and function, is reported to be common and crucial for plant survival in arctic and alpine environments, yet the phenomenon is remarkably little studied. In order to understand the role of preformation in the ecology and evolution of tundra species, this investigation takes a developmental and architectural approach to the analysis of plant growth and reproduction in the alpine perennial Polygonum viviparam L. Analyses show that the extent and duration of preformation in P. viviparam are extraordinary. Four years are required for each leaf and inflorescence to progress from initiation to functional and structural maturity. This single salient feature of development has profound consequences for basic architecture, dynamics of resource allocation, and the timing of plant responses to environmental variation. As a consequence of the protracted duration of leaf and inflorescence development, five cohorts of primordia, initiated in successive years, are borne simultaneously by an individual plant. In the year prior to maturation leaves reach 30% of their maximum size, and the maximum potential reproductive output of each inflorescence is determined. Thus, developmental processes that affect final morphology and resource allocation occur at least 1 yr before functional maturity. From the developmental and architectural models constructed for P. viviparum, a 1-yr delay in measurable plant responses to environmental variation is predicted. The models also apply generally to arctic and alpine species and provide a mechanistic explanation for observed patterns of productivity at the community and ecosystem scale.

Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years.

Unisexual flower morphology was examined within a phylogenetic context in order to identify developmental transitions associated with the multiple origins of dioecy in flowering plants. Historically, two categories of unisexual flowers have been recognized: type I flowers exhibit rudiments of the nonfunctional organ type, while type II flowers bear no vestigial sexual organs. Mapping of these flower types onto a composite phylogeny shows that type II morphology is homoplasious and has resulted from at least four distinct evolutionary developmental pathways. The historical assignment of unisexual flowers into only two morphological types has masked important developmental and evolutionary dynamics.