There is nothing more emblematic of spring and summer than flowers, but why do plants have flowers, and how did they evolve?

Botanists know that flowering plants, that is, plants that reproduce by producing seeds, evolved from non-flowering plants. According to evolutionary theory, nature would have selected plants with flowering tendencies because it gave these plants a reproductive advantage. It's within the protective casing of flower petals, after all, that flowers are pollinated and make seeds. The strategy has been hugely successful. The vast majority of plants today are flowering plants.

The precise origin of flowering plants, though, is puzzling. In fact, exactly when, how, and why plants first developed flowers remains one of the biggest mysteries of evolutionary paleontology.

However, two discoveries have begun to unravel the mystery of how plants got flowers. Four years ago, scientists in China found a fossil of the oldest known flowering plant. The reed-like plants lived at least 125 million years ago in a lake, suggesting that flowering plants first evolved in water. The scientists speculate that the plant's seeds floated along the shore and germinated near the banks.

More recently, scientist William Friedman of the University of Colorado found a clue in a plant called Amborella trichopoda, which grows in South Pacific rain forests. The plant's female reproductive system has an extra, sterile egg cell. Friedman thinks that the extraneous part is a remnant from a more primitive reproductive apparatus and could link the plant to non-flowering plants like pines and firs.

The origin of flowers is still a difficult puzzle, of course, but with further discoveries and research, flowering plants will become a bit less mysterious.