Drepanophycales
| Drepanophycales | ||||||||||||
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Asteroxylon sp. |
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| Devon | ||||||||||||
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| Scientific name | ||||||||||||
| Drepanophycales | ||||||||||||
The Drepanophycales are the oldest group of bear moss plants (Lycopodiopsida) and only known from the Devonian .
features
The Drepanophycales were probably herbaceous plants . The upright axes have an exact maturation of the primary xylem . On the axes there are helically arranged appendages, which are sometimes almost whorled . These appendages are either free of vascular bundles or partially traversed by vascular bundles: The bundle extends into the proximal part, but does not extend through the entire structure. They are more like microphylls than real leaves . In contrast to those of the protolepidodendrales , the appendages are not dichotomously branched at the tips.
The sporangia probably did not stand together in cones. They are also not adaxially on the sporophylls as in other club moss plants, but arise directly from the stem axis just above an appendage, i.e. axially. All representatives are homospor , so they only form one kind of spores .
Systematics
The Drepanophycales are the oldest known group of bear moss plants. Sometimes they are also seen as a transition group from the Zosterophyllophyta to the real bear moss plants. They do not yet have all the typical characteristics of the bear moss plants. In the cladistic analysis by Kendrick and Crane (1997), the representatives examined by them are at the base of the club moss plants.
Taylor, Taylor and Krings (2009) list the following genera :
- Asteroxylon is one of the characteristic plants of the Rhynie Chert .
- Baragwanathia is known from the Silurian- Devonian rocks of Australia and is therefore one of the oldestclub mossplants.
- Drepanophycus is a poorly defined genus with sickle-shaped appendages.
- Halleophyton morphologically resembles Drepanophycus , the leaf bases are rhomboid to hexagonal, the sporangia open with two equally sized valves. It comes from the early Devonian of China.
- Haplostigma with Haplostigma baldisii has microphyll-like appendages that are simple and have approximately hexagonal bases.
- Haskinsia was previously assigned to Drepanophycus . The screw-like appendages are sickle-shaped and around 3 mm long. The metaxylem consists of various forms of courtyard pits . In Haskinsia hastata , the appendages are arranged in pseudo whorls and around 5 mm long. The sporangia are spherical.
- Hestia eremosa is quite original, its systematic position is uncertain. It was described from the Mississippium of Oxroad Bay , East Lothian (Scotland). The shoot axes have a star-shaped stele , ladder tracheids
- Smeadia from the Upper Devonian of the Cleveland Shale of Ohio combines characteristics of several groups of Bärlapp: It was herbaceous with a siphonostele and spirally arranged leaves. At the distal end there was an upright cone, in the sporangia of which triled spores 40 to 80 µm in diameter were formed.
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. 268-271.
Individual evidence
- ^ Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study . Smithsonian Institution Press, Washington DC 1997, p. 213, ISBN 1-56098-729-4
