The study of fossil pollen grains by a group of researchers, including Kew scientists, revealed the daisy family, Asteraceae, to be 20 million years older than previously assumed.
'Fossil finds like this are hugely important in our task to fill in the gaps of knowledge on the evolution of plants, adding a crucial calibration point to the tree of life. In the case of the Asteraceae family, we can now safely say that the oldest daisies were probably trampled by the last surviving dinosaurs – this would probably come as a great surprise to most gardeners!', explained Luis Palazzesi, Marie Curie Fellow from Kew.
Asteraceae are the single most diverse family of flowering plants, made up of about 23,000 species. The family includes many popular garden plants and edibles such as daisies, sunflowers, chrysanthemums, lettuce and artichokes.
Because the fossil evidence was scarce researchers were previously unable to explain why such a large family didn’t have a longer history; discovering daisies evolved at an earlier time resolves this puzzle.
Advancing our understanding of the tree of life
As Luis explains discovering and dating these fossil pollen grains from Antarctica will help to show how and when the daisy family spread throughout the world, as well as its potential influence on the evolution of pollinators:
'This discovery will allow us to begin to unearth how this enormous family, dominant for the past several millions of years, expanded outside of Antarctica and other Gondwanan continents. It also has important implications for our understanding of pollinators, with Asteraceae regarded as one of the most influential families in both the diversification and evolution of animals such as bees, hummingbirds and wasps. Now we can begin to unlock how the Asteraceae family tree expanded.'
Constructing a detailed plant family tree might sound like quite an abstract scientific project. However, it provides the backbone for understanding how our ecosystems function, as well as delivering a tool for identifying plants that will provide future sources of food and medicine.
Analysis shows the daisy family is around 80 million years old
The fossil used as the basis for the research had remained buried for more than 65 million years. The deposits which were found in Antarctica contained other extinct groups such as dinosaurs and ammonites.
Scientists were able to demonstrate fossil specimens were part of the daisy family by comparing samples to pollen grains from several groups of flowering plants. They found very similar morphological features in both the fossil pollen and the pollen grains produced by Asteraceae today. However, the fossil pollen could be shown to belong to an extinct lineage, as it shared some but not all features with a living member of the family. This, and other analyses, revealed the Asteraceae family to be about 80 million years old. The fossil pollen grains belong to the species Tubulifloridites lilliei.
Using the Antarctic findings, the team has also now been able to unambiguously place a number of other Cretaceous fossilised pollen grains from New Zealand in the Asteraceae family. This implies that the Cretaceous distribution of this family was relatively broad, making it likely that once this family had evolved it spread rapidly across the Earth.
Institutions involved in the study:
Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (CONICET), Argentina
Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, UK
Laboratorio de Sistemática y Biología Evolutiva Museo de La Plata, Argentina
Centro Austral de Investigaciones Científicas, Tierra del Fuego, Argentina
Department of Palaeontology, GNS Science, New Zealand
Read the full paper: Early evolution of the angiosperm clade Asteraceae in the Cretaceous of Antarctica
The plant family tree
Professor Mark Chase, Senior Research Professor at Kew, explains how scientists are compiling the plant family tree.