Flowering plants - from corn, wheat, rice and potatoes to maple, oak, apple and cherry trees as well as roses, tulips, daisies and dandelions and even the corpse flower and voodoo lily - are cornerstones of Earth's ecosystems and essential for humankind.
New research based on genome data for 9,506 species, as well as an examination of 200 fossils, provides the deepest understanding to date of the evolutionary history of flowering plants, called angiosperms - the largest and most diverse plant group. It details how angiosperms appeared and became dominant during the age of dinosaurs and how they have changed over time.
The scientists devised a new tree of life for angiosperms, covering 15 times more types of flowering plants - nearly 60% of them - than the nearest comparable study.
"It is a massive leap forward in our understanding of plant evolution," said botanist William Baker of the Royal Botanic Gardens, Kew (RBG Kew) in London, senior author of the research published on Wednesday in the journal Nature.
Angiosperms, plants that produce flowers and generate their seeds in fruits, encompass about 330,000 species and comprise about 80% of the world's plants. They include, among others, all the major food crops, grasses, most broad-leaved trees and most aquatic plants. Their closest relatives are the gymnosperms, a group that preceded them on Earth and includes conifers and some others, with a bit more than 1,000 species.
The study identified two pulses of diversification among angiosperms. The first one occurred around 150-140 million years ago at the dawn of their existence during the Mesozoic era, with 80% of major angiosperm lineages arising during that time. The next one happened about 100 million years later during the Cenozoic era, after the demise of the dinosaurs and the rise of mammals, amid decreasing global temperatures.
"Angiosperms have many structural adaptations that confer advantages over gymnosperms, but chief among these are those contributing to reproductive success," Baker said.
Gymnosperms and angiosperms both have seeds, but the flowering plants have enclosed seeds that protect them from dehydration and enable them to prosper in a wider range of environments, from tropics to deserts to Antarctica.
They also evolved the flower, a structure that allowed them to form relationships with animal pollinators, especially insects, while gymnosperms usually rely upon the wind for pollination. Angiosperms evolved a high diversity of fruit types, permitting effective seed dispersal.
"With these innovations, angiosperms have become invincible," Baker said.
Charles Darwin, the 19th century British naturalist and architect of evolutionary theory, was astonished by how flowering plants exploded onto the scene in the Mesozoic fossil record.
In an 1879 letter to Joseph Hooker, RBG Kew's then-director, Darwin wrote that "the rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery."
"Remarkably," Baker said, "we have been able to use the 'molecular fossil record,' the accumulated change in DNA over time, to see real evidence of that explosion happening at the dawn of the angiosperms."
Flowering plants provide the majority of calories consumed by humans - grains, fruits and vegetables - including indirectly as feed for livestock. They also have enthralled people with their beauty - fields of sunflowers, bouquets of roses, bunches of calla lilies - and their pleasant fragrance.
"They are sources of many of our medicines and hold potential solutions to global challenges, such as climate change, biodiversity loss, human health, food security and renewable energy," Baker said.
The study could help scientists better understand disease and pest resistance in angiosperms and navigate potential new medicinal uses - for example, to combat malaria.
"Combining the tree of life with extinction risk assessments for each lineage allow us to prioritize lineages for conservation based on their uniqueness," RBG Kew botanist and study lead author Alexandre Zuntini said. "This is extremely important for mankind, as these lineages may hold chemical compounds or even genes that can be useful for survival of our species."
