Peltaspermales
| Peltaspermales | ||||||||||||
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Lepidopteris stuttgartiensis |
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| Temporal occurrence | ||||||||||||
| Upper Carboniferous to Triassic | ||||||||||||
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worldwide |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Peltaspermales | ||||||||||||
The Peltaspermales are a Mesozoic order of the extinct plant group of seed ferns .
features
leaves
Lepidopteris is the most common leaf genus of the Peltaspermales on Gondwana , but occurs on both hemispheres. The leaves are double-pinnate, pinnate still stand between the leaflets. Small vesicles sit on the epidermis , a feature that also characterizes other organs.
Callipteris is widespread in the northern hemisphere from the Carboniferous to the Triassic. In the past it was considered a biostratigraphic marker for the lower Permian. Several species of the genus were transferred to new genera: Rhachiphyllum , Lodevia , Arnhardtia , Sphenocallipteris and Dichophyllum . The most common fossil is Callipteris conferta with double to triple pinnate fronds and alethopteroid leaflets: they sit at an acute angle on the rachis , the base runs down on the lower side, the supply is provided by a vascular bundle that branches out into bifurcations and so strongly curved lateral nerves forms. Other leaf genera that belong to the Peltaspermales are Tatarina, Scytophyllum, Vittaephyllum and Pursongia from Russia.
Pollen organs
Antevsia are double-pinnate, planar microsporophylls, on which the primary side branches (leaflets) alternate. These are divided into two to five side branches, on each of which there are four to twelve sessile pollen sacs on the abaxial side. The rachis and primary branches show vesicular swellings.
The pollen grains are oval, 30 to 40 µm in size, monosulcat (a germ groove) and have smooth walls. They correspond to the taxon Cycadopites .
Sperm-forming organs
The most common genus is Peltaspermum , which consists of a central axis with alternate side branches in one plane. Each branch has a lobed disc or head at the end. In Peltaspermum thomasii this head sits with the edge on its stem and has two ovules on the underside. In Peltaspermum rotula , the disc sits like a shield on the stem and carries 10 to 12 ovules.
Autunia has helically arranged, bilaterally symmetrical megasporophylls, which sit with a marginal stalk on the central axis. The sporophylls are flat and leaf-like, with one or two ovules on the underside. To Autunia includes the leaves of Callipteris conferta and the pollen-organs Ptermostrobus gimmianus .
The affiliation of Supaia from China and Karibacarpon from Zimbabwe to the Peltaspermales is not completely clear.
distribution
The Peltaspermales are known worldwide from the Upper Carboniferous to the Triassic .
Systematic position
The Peltaspermales should not represent a monophyletic group. In cladistic analyzes of the seed plants, representatives of the Peltaspermales were found both as a sister group of the Corystospermales and below the clade (Anthophyta + recent Nacktsamer).
supporting documents
- Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants . Prentice Hall, Englewood Cliffs 1993, pp. 579-585. ISBN 0-13-651589-4
- EL Taylor, TN Taylor, H. Kerp, EJ Hermsen: Mesozoic seed ferns: Old paradigms, new discoveries . Journal of the Torrey Botanical Society, Volume 133, 2006, pp. 62-82