In many plants, flowers occur in inflorescences, clusters that develop through almost mathematical branching patterns. These patterns strongly impact the size and number of seeds and the success of pollination, which is why they are often conserved by natural selection over long evolutionary periods. But Elizabeth Kellogg from the University of Missouri, together with colleagues from Brazil, the UK, and Australia, here shows that around 40 million years ago there was an abrupt evolutionary transition in the branching pattern of inflorescences of cool-season grasses (subfamily Pooideae).
Through a series of Scanning Electron Microscopy images, Kellogg and colleagues show that inflorescences of most cool-season grasses grow in a "distichous" pattern, that is, in two opposite ranks of flower-bearing branches.
Furthermore, this branching is oddly asymmetrical, with most branches forming on one side of the inflorescence. In contrast, inflorescences of most other grasses retain the ancestral arrangement of branches in a spiral, which is likewise retained in the inflorescences of the most basal genus of the cool-season grasses.
The evolutionary innovation identified by Kellogg and colleagues helps to explain the great evolutionary success of this group, with contains approximately 3800 species spread across the Northern hemisphere, including important crops like wheat, barley, and oats.
Article: DOI:10.3389/fpls.2013.00250