Evolutionary History of the Leguminous Flower

The contemporary evolutionary developmental biology includes molecular phylogeny, studies on morphology and morphogenesis, genetics, and genomics. The most reliable conclusions about main trends of floral evolution can result from investigations of highly polymorphic group, which is precisely characterized from the positions of both modern systematics and molecular developmental biology. The legume family, Leguminosae, is a group of such kind. It demonstrates an outstanding variation in flower structure. The ancestral floral structure in this family includes monosymmetry, pentacycly, pentamerous perianth and androecium, and a monomerous gynoecium. However, distinct evolutionary lineages resulted in origin of polysymmetric perianth, different patterns of staminal reduction or polymerization, as well as multicarpellate gynoecium. A strikingly high level of homoplasy is found in Leguminosae. Besides the existing evolutionary tendency to stabilize floral structure, the exact “instability syndrome” evolved repeatedly, associated with a polysymmetry and characterized with a highly variable number and position of floral organs.