THE ancestors of plants that use seeds to reproduce began diverging from other plants around 385 million years ago.
When land plants appeared about 450 million years ago they reproduced by releasing spores. The oldest known seeds date from 365 million years ago, but several types are known, so they must have evolved earlier. Now a new examination of a little-known, 385-million-year-old plant fossil called Runcaria has helped pin down when this occurred.
Philippe Gerrienne of the University of Li猫ge in Belgium reports that Runcaria, which is a centimetre long and a few millimetres wide, has a central column with a phallus-shaped tip that caught wind-blown pollen. Filaments spiral down from the tip to the base like streamers on a maypole, with four lobes protecting an enlarged megaspore at the base, which the pollen fertilised.
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The whole structure is a precursor of later seeds, Gerrienne says, because in later plants the filaments fused and evolved into the seed coat that protects the embryo from drying (Science, vol 306, p 856).
While Runcaria was not a true seed because it lacked a sealed coat, says David Dilcher of the University of Florida in Gainesville, it was 鈥渁 pioneering breakthrough in reproduction potential for land plants鈥�.