What Charles Darwin famously called "an abominable mystery", the apparent sudden appearance and rapid spread of flowering plants in the fossil record, is the topic of a paper which proposes new evidence that flowering plants - angiosperms - evolved and colonized various types of aquatic environments over about 45 million years in the early to middle Cretaceous Period.

The researchers draw on fossil data from Europe to create a picture of how angiosperms evolved, and it connects their evolution with changes in the physical and biological environments. They say the scenario is consistent with findings from the fossil record in North America.

Darwin wrote to Joseph Dalton Hooker in 1879, about 20 years after the publication of "On the Origin of Species," that the rapid development of higher plants in recent geological times was "an abominable mystery." Solving the puzzle has fascinated biology, with competing ideas seeking to explain how angiosperms supplanted ferns and gymnosperms in many regions of the globe.

In the new paper, the researchers write that angiosperms successfully invaded certain environments, gradually spreading to others. They write that angiosperms migrated to new environments in three phases:

  • Freshwater lake-related wetlands between 130 million and 125 million years ago
  • Understory floodplains between 125 million and 100 million years ago
  • Natural levees, back swamps and coastal swamps between 100 million and 84 million years ago

Though once focused on collecting fossil flora and trying to make connections with present-day varieties,  Indiana University paleobotanist David L. Dilcher and colleagues in Europe  have produced new insights into the evolutionary biology of flowering plants through close analysis of morphology and anatomy.

Dilcher added that co-evolution with insects gave angiosperms an evolutionary advantage. Insects played a vital role in cross-pollinating plants and accelerating the spread of genetic material. Plants evolved the means to "advertise themselves" with fragrances and bright colors while producing pollen and nectar that provided food for insects.

Published in PNAS