Cladoxylopsida

Eospermatopteris erianus, roots

Features

The vascular system consists of a variable number of segments ( plates) of primary xylem and radially extending ribs of primary xylem. The position of the protoxylem strands is variable, but usually at the end of Xylemplatten. This arrangement was originally referred to as Polystele, but is now no longer seen as correctly. The occurring only at the Cladoxylopsida vasculature structure could have evolved from a aktinostele. The position of the small protoxylem elements similar structures in some other groups earlier farnähnlicher plants, their structures known as peripheral loops. Some fossils also secondary xylem is known.

The size of lateral branches indicates that at least some representatives were large plants.

In the cortex there are nests of sclereids.

System

Taylor, Taylor and Krings put two orders in the class Cladoxylopsida:

• Pseudosporochnales
• Iridopteridales

The earliest representatives come from the Middle Devonian, some species extend into the Mississippian ( Tournaisian ). It is believed that the Cladoxylopsida have developed from the Trimerophytophyta. They should not be a direct precursor of them following groups of plants.

The group itself is considered to be paraphyletic.

Because of the few distinctive features and the incomplete fossils, the systematic position of the Cladoxylopsida is quite unclear. One hypothesis is that they form with the ferns and Sphenophyta a monophyletic group Moniliformopses. A second hypothesis is that they form a group with the Rhacophytales and Zygopteridales. A third it provides within the Sphenophyta, a fourth sees them close to the genuine ferns.

Documents

• Thomas N. Taylor, Edith L. Taylor, Michael Krings: Paleobotany. The Biology and Evolution of Fossil Plants. Second Edition, Academic Press 2009, ISBN 978-0-12-373972-8, pp. 387-401.