Cooksonia were just a couple of centimetres high. They grew directly beside rivers or sea coasts . They probably had no roots.
These plants were extremely small: just a couple of centimetres high. From the deposits in which they have been found, researchers conclude that they grew directly beside rivers or sea coasts and were regularly submerged by the water.
It is not clear how they were attached to the soil. They probably had no roots, but stems growing horizontally over the ground. On top of these stems, there were bud- or saucer-shaped sporangia containing the spores that enabled the plant to reproduce. Ferns still reproduce this way.
The earliest Cooksonias have been found in Ireland and are 425 million years old. Cooksonias could grow taller than mosses and in drier places because they had a vascular system that conducted water to their tops.