A team of paleontologists led by Oxford University researcher Prof. Liam Dolan has discovered the oldest known population of plant root stem cells in a fossil 320 million years old (Carboniferous period). The discovery was detailed in a paper published this week in the journal Current Biology.

Stem cells – self-renewing cells responsible for the formation of multicellular organisms – are located in plants at the tips of shoots and roots.

The 320 million-year-old stem cells discovered by the team, which gave rise to the roots of an ancient plant, were found in a fossilized root tip from a Carboniferous coal swamp forest.

As well as revealing the oldest plant root stem cells identified to date, the research also marks the first time an actively growing fossilized root has been discovered – in effect, an ancient plant frozen in time.

Prof. Dolan and his colleagues have named the stem-cell fossil Radix carbonica (Latin for ‘coal root’).

The Carboniferous stem cells are different to all those living today, with a unique pattern of cell division that remained unknown until now.

That tells paleontologists that some of the mechanisms controlling root formation in plants and trees have now become extinct and may have been more diverse than thought.

These roots were important because they comprised the rooting structures of the plants growing in the Earth’s first global tropical wetland forests with tall trees over 160 feet (50 m) in height and were in part responsible for one of the most dramatic climate change events in history.

The evolution of deep rooting systems increased the rate of chemical weathering of silicate minerals in rocks – a chemical reaction that pulled carbon dioxide out of the atmosphere, leading to the cooling of the Earth and thus one of the planet’s great Ice ages.

“These fossils demonstrate how the roots of these ancient plants grew for the first time. It is startling that something so small could have had such a dramatic effect on the Earth’s climate,” Prof. Dolan said.

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Alexander J. Hetherington et al. 2016. Unique Cellular Organization in the Oldest Root Meristem. Current Biology 26 (12): 1629-1633; doi: 10.1016/j.cub.2016.04.072