The study of plant fossil is an important part of modern science. By observing plant fossils and their structures, scientists can clarify questions about the origin of life and evolution of species. The earliest known plant fossil are from the Silurian and Devonian periods, from 443 to 359 million years ago, and include Cooksonia, Baragwanathia, Nematothallus, Parka and Pachytheca fossils.
Cooksonia are the first fossils of macroscopic land plants, dated 425 million years old. They have been found in many locations, including Ireland, Wales, Scotland, England, Czech Republic and Canada. These plants were less than two-inches high, reproduced through spores and became extinct in the Early Devonian, from 416 to 359 million years ago. Cooksonia paranensis is the most recent species in this genus. It was found in 2001 in Brazil. (ref.2)
The first occurrence of Baragwanathia date from Late Silurian, about 420 million years ago. This was a club-moss-like plant, with stems of up to 8 inches,which were covered with needle-like leaves. Baragwanathia longifolia fossils have been found in Australia and Canada (ref. 3). These plants also reproduced through spores, and were the first vascular plants, with internal vessels to distribute the sap, bearing leaves.The Melbourne Museum, in Australia, has a baragwanathia fossil on display. (ref. 4)
Nematothallus fossils show a primitive cell structure, consisting of capillary threads or tubes, and an external cuticle dotted with pores. Nemtothallus were extinguished more than 300 million years ago, but some species of modern lichens resemble this primitive plant. However, the evolutionary link is not entirely clear. Nematothallus fossils were found across the United Kingdom.
Parka and Pachytheca
Parka fossils are abundant in Forfar, Scotland. They were small circular plants of humid to aquatic habitats, with up to 3 inches in diameter and internal spores, which were first discovered in a fossil in 1891. Before that, Parka decipiens fossils were mistaken for snail’s eggs, frog-spawn or berry fruits (ref. 5). Pachytheca fossils are smaller than Parka, but equally circular and dotted with spores. Both plants were living species at 400 million years ago.