Pseudosporochnales
| Pseudosporochnales | ||||||||||||
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Eospermatopteris erianus , roots |
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| Temporal occurrence | ||||||||||||
| Devon to Mississippium | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Pseudosporochnales | ||||||||||||
| Emberger |
The Pseudosporochnales are an extinct group of plants that are systematically close to the base of the ferns . With Eospermatopteris it belongs to the oldest known tree-shaped plants.
features
Many representatives of the Pseudosporochnales are now considered to be tree-shaped. With some representatives there are three-dimensional appendages at the last branches, with others flattened, foliage-like structures. The sporangia are terminal and are usually paired. With some representatives they are grouped together and are in pseudo whorls . All species are regarded as homospor (only spores of the same size ).
Systematics
The Pseudosporochnales are related to the Cladoxylopsida due to their stele structure .
- Cladoxylon
The genus Cladoxylon was established by Unger in 1856 for anatomically preserved stem axes . Today the genus is used by most authors as a form of fossilized shoot axes with a characteristic anatomy, with the primary xylem being at least partially divided into segments. Cladoxylon radiatum comes from the Mississippium of Germany. The stem axes have a diameter of up to 6.5 cm and have around 17 stele segments. The side branches are spiraling. There is only primary xylem with ladder tracheids . Thick-walled cells occur in the base tissue of the trunk. When lateral axes develop, four to six xylem arms branch off into the petiole , branch out further and form a flattened ring of up to eight xylem strands. With the Cladoxylon taeniatum , which is only 3.5 cm in diameter, there are two stele zones in the trunk. Around the trunk periphery there are numerous but less than 20 radially elongated xylem strands; in the center of the trunk there are three to four cylindrical xylem strands. Each of these produce bipolar leaf traces (with two protoxylemic poles).
Several finds with cladoxylopsid anatomy have been described from the Mississippium of Scotland. Cladoxylon waltonii is known to have stem axes and petioles of two size classes. One group comprises radially symmetrical stems with a diameter of less than 1.2 cm and helically arranged petioles with clepsydroid-like (dumbbell-shaped) xylem strands. The second group includes small stems 2 to 7 mm in diameter with alternate petioles. The larger stems have 9 to 15 xylem arms, the smaller 4 to 9, which are in a U-shape.
- Polyxylon
Polyxylon australe from the Upper Devonian Australia has small stem axes with a diameter of 2.7 cm. In the cross section one can see 19 elongated, mesarche arms of primary xylem (mesarch: the protoxylem is in the middle of the metaxylem, the maturation of the xylem takes place from the middle inwards and outwards). Each of the arms branches dichotomously at the end and forms at least six tracks that move into the swirling side axes.
- Hierogramma
Small shoot axes are known from Hierogramma , which have a bilateral vascular system with two elongated xylem bands, one of which is T-shaped. The vascular system then becomes a little higher in a U-shape. In Hierogramma mysticum , the leaf traces alternate as small, circular strands.
- Pseudosporochnus
Pseudosporochnus nodosus was reconstructed as a small tree with a bulbous base. It should have been 2 to 4 m high. The side axes are likely to have been thrown off after a certain time. The side branches branched dichotomously several times. The last branches are three-dimensional. There is hardly any distinction between sterile and fertile units; the latter have pairs of seated, ellipsoidal sporangia . The sporangia are up to 3 mm long. The spores are unknown. On all parts of the plants there are round-elongated structures, these represent nests of bark fibers.
Pseudosporochnus hueberi is native to the Middle to Upper Devonian in eastern New York . The axes are up to 58 cm long and several centimeters in diameter. There are 40 to 50 xylem segments in the main axis and 20 to 25 in the side axes.
- Wattieza
Wattieza givetiana comes from the central Devon of Belgium. There are also finds from Venezuela. The branches are even more branched than in Pseudosporochnus , the last axes are three-dimensional.
- Lorophyton
Lorophyton from the Givetium has forked roots, the side branches are partly dichotomous. The last lateral axes also branch dichotomously. The fertile units consist of the last segments bent back, each of which has two sporangia.
- Eospermatopteris
Eospermatopteris was first described by Winifred Goldring in 1924 based on finds from the Middle Devonian by Gilboa ( New York ). At that time only trunk spouts were known. The plant has been estimated to have been around 9 to 12 m tall, with massive, fern-like fronds and seeds at the ends of the branches. Eospermatopteris was thus considered the oldest seed fern for some time . In 2007 more finds were published. These findings showed that Eospermatopteris had a crown of short, upright Wattieza- type twigs that are finger-like and whose last appendages are three-dimensional. Real leaves are missing. The findings suggest that the plant was around 8 m high. The branches were regularly shed and replaced with new branches at the top of the plant.
- Pietzschia
Pietzschia is anatomically similar to Pseudosporochnus . The trunks have a diameter of around 2.5 cm and have a cylinder made of radially arranged xylem plates. In Pietzschia polyupsilon from the New Albany Shale of Kentucky , the number of xylem segments is 54. In some places there are sclerenchymal plates between the xylem segments . The track in the side axes is formed by four bundles. A little further from the junction, these strands form an inverted U-shaped strand. The main axis of Pietzschia polyupsilon had determined (limited) growth, the side axes were arranged in a whorl. Pietzschia levis from the lower Famennium (Upper Devonian) of Morocco has ground tissue with aerenchyma and lived in wetlands. Pietzschia schulleri , also from the Famennium of Morocco, has only primary tissue. The trunk diameter is often over 15 cm, the trunk has both central and peripheral xylem cords.
- Xenocladia
A liana habit was suggested for Xenocladia from the middle to late Devonian . Specimens of Xenocladia medullosina are around 10 cm in diameter and have secondary xylem.
- Stenoxylon
Stenoxylon has abundant secondary and reduced primary xylem. Stenoxylon ludwigii has vascular segments that anastomose and thus form a complex network of vascular systems. There are numerous small leaf stalks in a spiral arrangement on the trunk. Stenoxylon irvingense from the New Albany Shale has more secondary xylem formation on one side of the xylem arm than on the other. The vascular bundles are rather circular. There are irregular strips of thick-walled fibers in the parenchymal base tissue.
- Rhymokalone
Rhymokalon trichium from the Upper Devonian of New York is known to have up to 3 cm thick stem axes. The side axes of the second and third order are in a helical arrangement. Cross-sections show a multi-ribbed strand of primary xylem less than 1.8 cm in diameter. The xylem consists of tracheid plates with parenchyma between them. The metaxylem has ladder and spotted tracheids. The cortex consists of elongated parenchymal cells .
- Duisbergia
Duisbergia mirabilis is native to the Central Devonian. The plant is reconstructed as an upright, unbranched trunk about 2 m high with a club-shaped base. At the top of the stem is a dense crown of leaves arranged in a tight screw. The leaves appear to be in vertical rows. The last segments consist of fan-shaped leaves around 5 cm long. There are stripes on the surface that indicate leaf veins. Well-preserved specimens have up to 60 ribbon-shaped xylem strips, which are interpreted as secondary xylem , which is arranged in a ring. Duisbergia macrociccatricosus resembles Pseudosporochnus in the trunk . Duisbergia could thus represent the lower stem part of Pseudosporochnus .
- Polypetalophyton
Polypetalophyton comes from the late Devonian of China and was first described in 2003. There are four side branches at each node, the internodes between them are long. The vascular system consists of several stripe-shaped strands of primary xylems located on the periphery. In the middle of the axis there is a central, circular vascular bundle . The sporangia are terminal on fertile branches. The sterile terminal segments are flattened and correspond to the Sphenopteridium type .
- Calamophyton
Calamophyton is a plant a few decimeters high with dichotomous branches.
Other genera that anatomically correspond to the Pseudosporochnales are Syncardia , Voelkelia and Arctopodium .
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. 388-398.
