Uncorrelated evolution of leaf and petal venation patterns across the angiosperm phylogeny


Early angiosperm evolution, beginning approximately 140 million years ago, saw many innovations that enabled ow- ering plants to alter ecosystems globally. These included the development of novel, ower-based pollinator attrac- tion mechanisms and the development of increased water transport capacity in stems and leaves. Vein length per area (VLA) of leaves increased nearly threefold in the rst 30–40 million years of angiosperm evolution, increasing the capacity for transpiration and photosynthesis. In contrast to leaves, high water transport capacities in ow- ers may not be an advantage because owers do not typically contribute to plant carbon gain. Although owers of extant basal angiosperms are hydrated by the xylem, owers of more recently derived lineages may be hydrated predominantly by the phloem. In the present study, we measured leaf and ower VLA for a phylogenetically diverse sample of 132 species from 52 angiosperm families to ask (i) whether flowers have lower VLA than leaves, (ii) whether owers of basal angiosperm lineages have higher VLA than more recently derived lineages because of differences between xylem and phloem hydration, and (iii) whether ower and leaf VLA evolved independently. It was found that oral structures had lower VLA than leaves, but basal angiosperm owers did not have higher VLA than more derived lineages. Furthermore, the independent evolution of leaf and petal VLA suggested that these organs may be devel- opmentally modular. Unlike leaves, which have experienced strong selection for increased water transport capacity, owers may have been shielded from such selective pressures by different developmental processes controlling VLA throughout the plant bauplan.

Journal of Experimental Botany