Iridopteridales
| Iridopteridales | ||||||||||||
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Reconstruction by Ibyka amphikoma Skog & Bank , 1973 |
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| Temporal occurrence | ||||||||||||
| Middle Devon to Upper Devon | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Iridopteridales | ||||||||||||
| WEStein |
The Iridopteridales are an extinct group of plants that can be found near the base of the ferns .
features
The representatives are characterized by a strongly fissured, ribbed protostele , which has permanent protoxylem strands. The vascular bundles branch off in whorls. The branching takes place iteratively, so the branching pattern is repeated several times in the higher-order side branches. Two types of lateral axes are formed at the nodes , each of which is supplied with a single vascular bundle trace that arises from a rib of the stele. The xylem is mesarchic, the largest tracheids are located near the center of the xylem ribs. The main characteristic by which the Iridopteridales differ from the otherwise similar Pseudosporochnales distinguish is the origin of the vascular bundle track on the stele rib.
Systematics
The systematic position of the Iridopteridales is unclear. They stand near the base of the ferns . Taylor, Taylor and Krings (2009) place them in the Cladoxylopsida with the Pseudosporochnales .
- Arachnoxylon
Arachnoxylon is a genus of anatomically preserved stele fragments. They have a ribbed protostele that consists only of primary tissue. In the cross-section at the end of each xylem arm there is a strand of protoxylem or a cavity that corresponds to a peripheral loop. There are three types of leaf marks, which differ in size and position. The lateral axes are in whorls. The primary xylem is mesarchic, the secondary wall of the tracheids is ladder-like or round to elliptical pits. There are two types, Arachnoxylon headii (Givetium of New York) and Arachnoxylon minor .
- Compsocradus
Compsocradus is native to the mid to late Devonian and is similar to Arachnoxylon . The finds are interpreted as pseudo monopodial with upright first-order branches. The last appendages are bent back. The fertile end in paired sporangia . Fertile as well as sterile appendages are in whorls, with the fertile ones up to 64 are in a whorl. Spores are not known. The stele consists of six ribs of primary xylems, each of which carries a strand of protoxylem at the top. The tracheids have single-row, round to oval pits.
- Iridopteris
Iridopteris has a five-ribbed protostele with a mesarchic xylem. Iridopteris eriensis has axes over 5.5 cm in diameter and shows two types of leaf marks. The smaller ones are round in cross-section and are created by radial division at the edge of the primary ribs. The larger tracks are elliptical and have a protoxylem strand at each end. Iridopteris is similar to Arachnoxylon , but differs from it in its bilateral symmetry and smaller size.
- Metacladophyton
Metacladophyton from the Givetium of China has whorled side axes of the first order with two to seven axes per whorl. The trunks are 1.5 cm in diameter, the lobed primary xylem forms a U-shaped stele
- Ibyka
Ibyka amphikoma comes from the middle Devonian and was initially counted among the Sphenophyta , only later was it assigned to the Iridopteridales. The plant has a monopodial branching system with whorled side axes. The appendages are formed by side axes on several orders. The plant is covered with delicate hair . The vascular system consists of a three-lobed stele. Some of the arms branch out in bifurcation and form rounded leaf marks. Protoxylem tracheids and parenchyma sit near the tip of the xylem lobe and form a persistent protoxylem. The sporangia on the last branches are egg-shaped and around 1 mm long. A species from the Middle Devon, originally placed in its own genus Hyenia , was also transferred to this genus in 2005 as Ibyka vogtii .
- Serripteris
Serripteris from the middle Tournaisium of southern France is provisionally counted among the Iridopteridales. It has several orders of side axes. The stele is four-ribbed and mesarch.
- Asteropteris
Astopteris from the late Devonian has a star-shaped protostele with conspicuous protoxylemic strands.
- Anapaulia
Anapaulia moodyi from the middle to late Devonian of Venezuela is provisionally counted among the Iridopteridales. It is reconstructed as a monopodial plant with side branches in pseudo whorls. The last side branches have bent back tips. The sporangia are elliptical. The whole plant is covered with delicate spines.
- Rotoxylon
Rotoxylon dawsonii from the late Devonian has a variable xylem. The xylem ripening takes place mesarchically, at the tip of each xylem arm there are one to three permanent protoxylem strands. The tracheids have elliptical to elongated pits . The classification to the Iridopteridales is not certain, the species could also belong to the Pseudosporochnales.
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. 398-400.