How Flowers Conqured the World

The great explosion in flowering plants during the Cretaceous Period is one of the great enigmas of evolution.

Charles Darwin had no explanation, calling it an "abominable mystery".

But now scientists think they have solved the riddle of how flowers came to dominate the conifers and ferns that preceded them.

The flowers' secret, they say, was to exploit a change in soil fertility, and create a feedback loop that allowed new flowers to feed off dead ones.

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Initially, gymnosperms flourished in poor soils. Such plants have longer-lived leaves which are capable of squeezing more nutrients out of the ground, but the litter they create tends not to decompose very fast. So while gymnosperms benefit from poor soils, they also do little to improve soil quality.

But then came some subtle changes in soil fertility. Angiosperms started colonising more fertile soils, gaining a foothold.

These early flowering plants then began changing the ecology of the soil. As they perished, they create a greater turnover in litter that replenished the soil, allowing yet more flowers to grow.

"From that time a positive feedback developed, where an increase in angiosperm dominance led to an increase in soil fertility and an increase in soil fertility led to a further accelerated expansion of the angiosperms," says Berendse.