Zosterophylls

The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta or Zosterophyta and the class or plesion Zosterophyllopsida or Zosteropsida. They were among the first vascular plants in the fossil record, and had a world-wide distribution. They were probably stem-group lycophytes, forming a sister group to the ancestors of the living lycophytes. By the late Silurian (late Ludlovian, about ) a diverse asse

Sawdonia is an extinct genus of early vascular plants, known from the Upper Silurian to the Lower Carboniferous (). Sawdonia is best recognized by the large number of spikes (enations) covering the plant. These are vascular plants that do not have vascular systems in their enations. The first species of this genus (Sawdonia ornata) was described in 1859 by Sir J. William Dawson and, was originally attributed to the genus Psilophyton. He named this plant Psilophyton princeps. In 1971 Francis Hueber proposed a new genus for this species due to its "Divergent technical characters from the generic

Zosterophyllum was a genus of Silurian-Devonian vascular land plants with naked branching axes on which usually kidney-shaped sporangia were arranged in lateral positions. It is the type genus for the group known as zosterophylls, thought to be part of the lineage from which modern lycophytes evolved. More than 20 species have been described.

The Sawdoniales are an order or plesion of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. In their major cladistic study of early land plants, Kenrick and Crane placed most of the zosterophylls in the Sawdoniales (which they treated as a plesion).