Two 400-million-year-old fossil plants are the oldest known examples of wood. They are small herbs, suggesting that wood did not evolve to help plants grow tall.
Both fossils date from the early Devonian period, by which time simple plants had long colonised the land and begun diversifying. One was found in France and dates from 407 million years ago, while the other, from Canada, is 397 million years old.
According to lead researcher Philippe Gerrienne of the University of Liège, Belgium, they predate the previous record-holders by at least 10 million years.
Trees would not evolve until about 385 million years ago, at which point they began scrambling to grow taller in order to capture more light. Wood was crucial for this, because it made their trunks sturdier.
But Gerrienne thinks that was not why wood first evolved. His fossils are stems only 12 centimetres long, so they wouldn't need the support. Instead he thinks the wood improved the flow of water up the stems.
Journal reference: Science, vol 333, p 837.
Image: Science/AAAS. This post originally appeared on New Scientist.