Cladoxylopsida
| Cladoxylopsida | ||||||||||||
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Eospermatopteris erianus , roots |
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| Temporal occurrence | ||||||||||||
| Devon to Mississippium | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Cladoxylopsida | ||||||||||||
| Pic.Serm. |
The Cladoxylopsida are an extinct group of plants that can be found near the base of the ferns .
features
The vasculature consists of a variable number of segments (plates) made of primary xylem and radially elongated ribs made of primary xylem. The position of the protoxylem strands is variable, but mostly at the end of the xylem plates. This arrangement was originally also called a polystele , but is no longer considered correct today. The vascular system structure that occurs only in the Cladoxylopsida could have developed from an actinostele . The location of the small protoxylemic elements resembles structures in some other groups of early fern-like plants, the structures of which are known as peripheral loops. Secondary xylem is also known from some fossils.
The size of side branches indicates that at least some representatives were large plants.
There are nests made of sclereids in the bark .
Systematics
Taylor, Taylor and Krings put two orders in the Cladoxylopsida class:
The earliest representatives come from the Middle Devon , some species reach into the Mississippian ( Tournaisium ). It is believed that the Cladoxylopsida evolved from the Trimerophytophyta . They should not be direct precursors of the plant groups that follow them.
The group itself is considered paraphyletic .
Due to the few distinctive features and the incomplete fossils, the systematic position of the Cladoxylopsida is quite unclear. According to one hypothesis they form a monophyletic group with the ferns and Sphenophyta , the Moniliformopses . According to a second hypothesis, they form a group with the Rhacophytales and Zygopteridales . A third places them within the Sphenophyta, a fourth sees them close to the real ferns .
supporting 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.
