The evolution of annual lifeforms is a repeated step in the evolution of angiosperms. Despite obvious advantages of a short life cycle, the annual lifeform embodies great risks, such as necessity for rapid growth, dependence on favorable weather and pollinating agents in a single season, plus competitive disadvantages with perennial species occupying the same sites. Annual species have evolved features to circumvent these risks, many of them associated with an "annual syndrome." This includes more rapid growth to maturity and sexual reproduction, reduced stature and number and position of inflorescences, smaller genome size (associated with a shorter cell cycle, allowing faster development), increased rate of molecular evolution (probably correlated with a shorter generation time), and reduction in phytochemical arsenals (perhaps related to lower risk of herbivory during a shorter life span). Other characters not as closely associated with the annual lifeform (e.g., ultrastructure of pollen and seeds) may, therefore, provide better evidence of phylogenetic history in annual taxa. A good system in which to address questions of the evolution of annual taxa from perennial sister species is in the annual species of Veronica (Scrophulariaceae). These taxa previously have been classified together in section Alsinebe (also called Pocilla), but different base chromosome numbers and seed morphology have long suggested that the group is polyphyletic. Molecular data from nuclear (ribosomal DNA, ITS) and chloroplast (trnL-F) strongly support this polyphyly. This provides the opportunity to study repeated morphological, karyological, and phytochemical trends and convergences during the repeated evolution of the annual lifeform in this genus.

Key words: annual lifeform, genome size, Lamiales, molecular evolution, molecular phylogenetics, Scrophulariaceae