Seed ferns
| Seed ferns | ||||||||||||
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Leaves of a Samenfarns from the Pennsylvanian of Ohio |
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| Temporal occurrence | ||||||||||||
| Carbon to chalk | ||||||||||||
| 360 to 65 million years | ||||||||||||
| Locations | ||||||||||||
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worldwide |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pteridospermopsida | ||||||||||||
The seed ferns or Pteridospermae (Pteridospermopsida) are an extinct group of seed plants . They do not represent a natural family group, but merely a level of organization or development. Some representatives from the Paleozoic era in a certain way occupy an intermediate position between ferns and other seed plants. Seeds and spores were formed on foliage leaves. Some Mesozoic representatives are associated with the evolution of the bed covers.
features
Some seed ferns were small trees with upright trunks, arranged in a spiral, with large, fern-frond-like leaves . Others were lianas. The structure of the stele was very different depending on the group and ranges from a protostele to an eustele. The wood is mainly composed of parenchyma and thin-walled tracheids . The cortex of many groups is characterized by longitudinally oriented sclerenchymal bands .
Seeds as well as the spore-forming structures were formed on leaves. Seeds were formed too many in many-seeded cups or individually. The spore organs stood together in clusters and in some groups formed a large, synangial organ.
Temporal and geographical distribution
The seed ferns first appeared in the Carboniferous , which began around 360 million years ago. The last representatives, the Caytoniales , died out in the Cretaceous , which ended 65 million years ago.
Systematics
Taylor and Taylor name the following orders:
- Paleozoic orders:
- Mesozoic orders: their systematic position within the seed plants and among each other are by no means clear.
- Caytoniales
- Corystospermales
- Peltaspermales
- Petriellales : from the Triassic of Antarctica
supporting documents
- Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants , pp. 558-574. Prentice Hall, Englewood Cliffs 1993. ISBN 0-13-651589-4
Individual evidence
- ^ A b Edith L. Taylor, Thomas N. Taylor, Hans Kerp, Elizabeth J. Hermsen: Mesozoic seed ferns: Old paradigms, new discoveries . Journal of the Torrey Botanical Society, Volume 133, 2006, pp. 62-82.