The Rest of the Iceberg. Legume Diversity and Evolution in a Phylogenetic Context

Most readers of a special issue ofPlant Physiology on legumes will be familiar with only a handful of species, primarily pea (Pisum sativum) and the various economically important “beans” such as soybean (Glycine max), and of course, the model legumesMedicago truncatula and Lotus japonicus. That leaves around 700 other legume genera and 20,000 species left to consider—legumes are the third largest flowering plant family, behind only orchids (Orchidaceae) and asters (Asteraceae). And the numbers tell only part of the story. Neither these two larger families, nor the grasses, another large group, even begin to approach the legumes in their overall range of variation. The legumes are incredibly diverse in every way imaginable and defy generalization about almost any attribute. Even the characteristic fruit type that gives legumes their name is highly variable and ranges from tiny single-seeded forms to meter-long woody pods and from typical dehiscent legumes to indehiscent wind-dispersed winged fruits and articulated loments with “stick-tight” dispersal strategies.