Ancient trees could grow roots "backwards."

It is not that the roots physically grew upwards or "backwards". Scientists are talking about something else: the lateral roots of these ancient plants formed in an unusual pattern, more akin to the development of shoots.

Details

The researchers studied Stigmaria fossils, which are the underground structures of ancient tree-like plaunas. These plants grew in the swamp forests of the Palaeozoic hundreds of millions of years ago and could reach tens of metres in height.

Their underground parts were long thought to be roots. The surface of such fossils shows rows of small depressions - traces of where thin lateral roots once ran off.

To understand how these structures were organised inside, scientists used microcomputer tomography. This is similar to a medical CT scan, but with much higher resolution. This method allows you to look at the internal structure of a fossil without destroying it.

The researchers scanned three well-preserved specimens and created three-dimensional digital models of them. Thanks to this, they were able to see how the channels connected to the lateral spines ran inside the main axis.

The result was unexpected. The lateral roots appeared near the top of the growing axis - roughly the way plants form lateral structures on shoots. In modern roots, development is usually organised differently.

This is why scientists speculate that Stigmaria may have been a special type of underground organ: not an ordinary root in the modern sense, but a structure that evolved from a shoot and over time began to fulfil a root function.

Why it matters

The finding shows that ancient plants were able to solve the task of growing and anchoring themselves in the soil in a very different way from modern trees.

Today, it seems obvious to us that roots and shoots develop according to different rules. But Stigmaria fossils show: in the distant past, plants could experiment with other variations in structure.

This is important for understanding how the first large forests emerged. Tree-like plaunas were among the main plants of coal bogs. It was such forests that later became the basis of many coal seams.

If their 'roots' were unusually arranged, it helps to better understand how these plants were held in the boggy soil, how they obtained water and nutrients, and why they were able to form huge ancient forests.

Background

Stigmaria have been known to palaeontologists for a long time. As early as the 19th century, scientists realised that these structures were associated with ancient trees like Sigillaria and Lepidodendron. They were found together with stumps, which helped to prove that the coal bogs were real ancient forests and not just clusters of plants brought by water.

But for a long time the question remained: were these underground structures the same roots as modern plants, or did they represent something more unusual.

The new study gives the answer: at least in the samples studied, the development indeed looked unusual and resembled the work of a shoot.

At the same time, scientists emphasise that so far only a few fossils have been studied. Therefore, it is impossible to assert that all ancient trees grew in the same way. But the discovery already shows that even well-known fossils can hide important details.

Source

The study by Michael P. D'Antonio and co-authors is published in Proceedings of the Royal Society B: Biological Sciences in 2026: A shoot at the root? Unique development and evolution of the stigmarian apical meristem. The scientists studied Stigmaria fossils using microcomputer tomography and showed that their underground structures may have evolved in an unusual, "shoot-like" pattern.