Plant reproduction by means of flowers has long been thought to promote the success and diversification of angiosperms. It remains unclear, however, how this success has been come about. A recent review by Scott Armbruster published in AoB PLANTS considers the role of reproductive factors in the evolutionary success of flowering plants, with emphasis on flowers and pollination. Flowers are complex structures that have varying degrees of integration of parts and surprising evolutionary lability. Diversification of floral form usually accompanies plant diversification by speciation. This correlation has traditionally been interpreted as the result of floral specialization increasing speciation rates. However, another possibility is that species diversity generates selection for divergent specialized flowers when related species occur together, thereby reducing extinction rates.
Early-diverging angiosperms are important for studies of the origin and early evolution of the flower. Vialette-Guiraud et al. discuss the potential of the water lily Cabomba (Nymphaeales) as a model basal angiosperm, as it combines simplicity of floral structure, numerous pleisiomorphic angiosperm characters, and practical features that make it amenable to study using a broad range of molecular biological techniques. They also provide protocols for the growth and molecular analysis of Cabomba, a Cabomba flower EST database, and a genome size measurement of C. caroliniana.
There is relatively little information avialable regarding the role of plant growth regulators in the germination of recalcitrant seeds. Pieruzzi et al. determine an increase in the ratio of the polyamines (spermidine + spermine) : putrescine in the embryos of germinating Araucaria angustifolia (gymnosperm) and Ocotea odorifera (angiosperm), which could be used as a marker for germination completion. An unexpected increase of ABA levels was observed in A. angustifolia embryos, which suggests a potential role for this rgeulator in some recalcitrant seeds.