From a prehistoric plant series that Alexis assembled over the summer:
Today’s first photo shows a fossilized specimen (about 2.5cm tall) of Cooksonia pertoni from Shropshire, England, dating from the Upper Silurian. Much thanks to Hans Steur for permitting us to share his work!
The second photo shows a model of Cooksonia found in the Evolution House at the Royal Botanic Gardens, Kew. Thanks to Drew (Drew Avery@Flickr) for sharing the photo! Along with fossils, these models can help us imagine what Earth’s early plant life may have looked like.
In 1937, British botanist William Henry Lang was the first to describe the extinct genus Cooksonia, based on specimens he found in Wales. From his findings, he identified two species: Cooksonia pertoni and Cooksonia hemisphaerica. Since then, more fossils of the genus dating from the Silurian to Lower Devonian have been found in Europe, Africa, and North America (see: Thomas and Spicer’s The Evolution of Palaeobiology of Land Plants (1987)). It should also be noted that Cooksonia is not considered to be an evolutionary clade (not all the species have a common ancestor), but rather it is a grade, a group in which species share similar morphology.
Cooksonia is often credited with being the “first vascular land plant.” Despite its reputation, however, it is uncertain whether all Cooksonia species were vascular. Some fossilized impressions show evidence of vascular tissue in the form of a dark strand in the centre of the plant’s axis, but not all Cooksonia specimens do. What is certain is that Cooksonia was a small plant, no larger than 15cm tall, possessing several distinctive features such as a dichotomous branching pattern, lack of true leaves, and sporangia found on the tips of the branches, that are now associated with other early land plants.