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Fossils from world's oldest trees reveal growth pattern never seen before

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oldest trees
Nature   A 374-million-year-old tree

Fossils from a 374-million-year-old tree found in northwest China showed that the first trees to have ever grown on Earth were also the most complex.

Writing in the journal Proceedings of the National Academy of Sciences, researchers from China, Britain and the United States said the trunk of the tree, about 70 cm in diameter, has an interconnected web of woody strands that is much more intricate than that of the trees we see around us today.

The strands, known as xylem, are responsible for conducting water from a tree's roots to its branches and leaves.

In the most familiar trees, the xylem forms a single cylinder to which new growth is added in rings year by year just un

er the bark. In other trees, notably palms, xylem is formed in strands embedded in softer tissues throughout the trunk.

The new fossils, found in Xinjiang, showed that the earliest trees, belonging to a group known as the cladoxlopsids, had their xylem dispersed in strands in the outer five cm of the tree trunk only, whilst the middle of the trunk was completely hollow.

The narrow strands were arranged in an organized fashion and were interconnected to each other like a finely tuned network of water pipes, they said.

"It is a chance event to find our silicified fossil," Hong-He Xu of the Nanjing Institute of Geology and Paleontology, part of the Chinese Academy Of Sciences, recalled in an email of his first discovery of the fossils in 2012.

"When I firstly saw the block, which is black and quite heavy and not looking as tree, only a few small cellular structures showing something of a plant."

Xu went back to Xinjiang for more fieldwork in 2015 and found in the next year the whole trunk in a remote and open desert area, a discovery he described as "new, special and unique."

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