ALBACH, DIRK C.* and MANFRED A. FISCHER. Institute of Botany, Department of Higher Plant Systematics, Rennweg 14, 1030 Wien, Austria. - Convergence and diversity in annual members of Veronica (Scrophulariaceae).
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