Zygopteridales
Alloiopteris erosa, Upper Carboniferous
Features
The representatives have elaborate, three-dimensional fronds the leaflets in four rows ( quadriseriat ) wear. The fronds have in cross-section characteristic stelae configuration, a C, E, H, I, X, or Y is similar and has been used to identify a subdivision of the order.
The sporangia are elongated and are available in large groups on the underside of leaflets, or at the tip of frond branches. The sporangia have significantly erkenntbare opening mechanisms ( annulus ). The annulus is V-shaped or consists of two longitudinal bands. Fertile fronds or at least the fertile frond parts are likely to be built morphologically different with most representatives.
The rachis is radial symmetry in cross section and is also known as Phyllophor to distinguish them from the C-shaped vascular bundles of the Real ferns. The Phyllophor has bipolar primary xylem strands, some have terminal loops. The tracks to the pinnae leave the Xlemstrang as crescent-shaped vascular bundles, of which branch off further bundles. The Zygopteridales are sometimes divided because of the frond morphology and anatomy in two groups: Etapteroiden with four rows of primary pinnules and open lateral loops; and the Clepsydroiden with two rows of primary pinnules as in living ferns, and an hour glass shaped in cross-section Phyllophor.
System
The Zygopteridales contain only one family, the Zygopteridaceae. This is provided by some authors in the order Coenopteridales. The family contains 13 genera and about 45-50 species.
The representatives are:
- Alloiopteris
- Asterochlaenopsis
- Austroclepsis
- Biscalitheca
- Brittsia
- Clepsydropsis
- Corynepteris
- Diplolabis
- Protoclepsydropsis
- Symplocopteris
- Yulebacaulis
- Zygopteris
Evolution
The Zygopteridales have evolved from clepsydroiden Phyllophor type to the forms of Zygopteris. In Viseum first appear on flat leaflets, but they always remain rather small.
Many features indicate adaptations to dry growing conditions and high light irradiance at the sites. Among them is the strong pubescence, the presence of locked shoot tips, which show a periodic dormancy.
The precursors of Zygopteridales may have been tree-like, as the earliest forms, the Clesydroiden, are also tree-like. These are unbranched ( Asterochlaenopsis ) or have a wrong root on ( Symplocopteris and Austroclepsis ).
A cladistic study saw the Zygopteridales together with the Pseudosporochnales and Rhacophytales in a clade, while the Stauropteridales and eusporangiaten and leptosporangiaten Ferns two clades formed.
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. 408-418.