Glossopteridales
| Glossopteridales | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Glossopteris spec. |
||||||||||||
| Temporal occurrence | ||||||||||||
| Permian to Triassic | ||||||||||||
| Locations | ||||||||||||
|
Australia, Africa, South America, Antarctica |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Glossopteridales | ||||||||||||
The Glossopteridales are an order of the extinct plant group of the seed ferns . They were widespread in the Permian on the southern continent of Gondwana , especially the eponymous genus Glossopteris , which is why this flora is called the Glossopteris flora . The tongue-shaped leaves are characteristic, from which the name is derived ( Greek glossis “tongue”, pteris “fern”).
features
Vegetative organs
From Glossopteris that they grew tree-like is assumed. The wood of Glossopteris is pyknoxyl (dense wood with little parenchyma) with distinct growth rings. It is sometimes placed in the morpho genus Araucarioxylon . Here the pits of the tracheids stand in rows on the radial walls, some pits are hexagonal. The xylem rays are uniseriate. The strain at Glossopteris skaarensis has a Eustele whose tracheides round bordered pits have.
The underground organs did not reach very deep and are placed in the genus Vertebraria . In the center is an exarches primary xylem surrounded by four to seven rays of secondary wood separated by cavities. The secondary xylem has growth rings. Around the secondary wood is a thin, corked periderm . The primary xylem is formed by ring tracheids, the secondary by spotted tracheids.
The leaves were alternate or arranged in tight screws on the axes. There are many indications that the leaves were on long and short shoots, similar to the ginkgo . Glossopteris shed its leaves in autumn. Most of the leaves are found individually.
Glossopteris is by far the most common genus. The leaves are lanceolate and have a pronounced midrib and network veins. Over 200 species have been described. One of the most common species is Glossopteris browniana , the leaves of which are over 30 centimeters long and have a rounded tip. The epidermis of Glossopteris fibrosa was examined: stomata are limited to the underside of the leaf and surrounded by four to eight accompanying cells . Some species have hair on the underside .
The leaf anatomy could only be examined in a few species. Glossopteris schopfii has four to five vascular bundles in the midrib . The vascular bundles are surrounded by a bundle sheath made of thick-walled fiber cells. The density of the stomata, which also only sit on the underside here, is 40 per mm². The midrib of Glossopteris skaarensis consists of a single, wide vascular bundle with ladder tracheids, which is surrounded by a thin-walled bundle sheath. Leaf stalks are also known for Triassic forms .
Gangamopteris is a genus that mainly occurred in the Lower Permian, its leaves do not have a distinct midrib. Other common leaf genera are Belemnopteris and Rhabdotaenia , while Rubidgea, Palaeovittaria and Euryphyllum are less common .
Reproductive organs
The reproductive organs - ovules and pollen sacs - are on leaves or on modified leaves. Male and female organs are always on separate leaves.
Ovules-bearing organs
The female organs consist of a dorsiventral structure on which the seeds are formed. This structure has been named differently: Capitulum, Megasporophyll, Cupula, Fertiliger. Some of these organs could have formed cones .
The morphology of the seed-bearing structures is very diverse compared to the vegetative structures. Some examples are:
- Scutum is a morpho genus whose ovules-bearing structure is shield-like. The central part, on which the ovules sit, is surrounded by a wing edge. Ottokaria has a slender stalk with a fan-like head, on the adaxially (towards the axis) sitting seeds. It is not certain whether the stalk arises from the midrib of the leaf or from the leaf axil. Austroglossa walkomii carries up to 20 sessile seeds on each stalked head, which are attached to the petioles of Glossopteris conspicua .
- Lidgeottia is a composite structure in which four to eight seed-bearing structures ( megasporophylls ) sit on a leaf. Each individual megasporophyll is disc-shaped and around seven millimeters in diameter. The edge is lobed to dentate. The seeds of the Samaropsis type have a diameter of two millimeters and are winged.
- In Rusangea from South Africa, two stems protrude from each leaf, each bearing only one seed. Rusangea elegans has leaves around 2.8 centimeters long with wingless, oval seeds 3.5 millimeters in size.
- Denkania has six seed-bearing cupules , each on a long stem on a Glossopteris leaf. Each is around an inch tall and carries only one seed.
- Megasporophylls of Glossopteris are known from the late Permian of Queensland , which are curled upwards. The approximately 1.5 mm large ovules are located in the cavity that is created in this way. The cavity is filled with filaments that may have played a role in steering the pollen grains.
Common seed forms are pterygospermum and stephanostoma .
Pollen-producing organs
Pollen-bearing organs were found much less often than those that bear seeds. One of the most common is Glossotheca : It consists of stalks that arise from the petiole of the leaf. At the end of the stalk there are groups of up to 100 elongated pollen sacs .
Individual pollen sacs that are assigned to the Glossopteridales are Arberiella , Lithangium and Polytheca , whose sporangia are unilocular. The pollen grains in Arberiella have two air sacs, so they are bisaccat. In Arberiella vulgaris , they are 85 micrometers long. In lithium the pollen grains are monolet (have only one scar), in Polytheca monocolpat (have a germinal furrow).
ecology
The Glossopteridales probably grew primarily on swampy terrain. This is concluded from the air-filled structures of the rhizomes.
They were adapted to a strongly seasonal climate, as they colonized the former major continent Gondwana up to high southern latitudes and developed clear annual rings. Thick layers of single leaves suggest that leaves are shed.
distribution
The Glossopteridales were widespread across the Gondwana continent and are now found in Australia, Africa, South America and Antarctica. They were the vegetation-defining clan in this area during the late Paleozoic .
Systematic position
The relationship of the Glossopteridales is not clear. They have characteristics of several groups, but are most similar to the seed ferns with which they are placed.
Schopf placed them near the Gnetales and suspected that the Glossopteridales were their ancestors. Cladistic investigations by Doyle and Donoghue placed them in the vicinity of the bedevils .
Botanical history
Glossopteris was first described in detail by Adolphe Brongniart in 1828. The Glossopteridales or their representatives were initially assigned to different groups, such as the cycads , seed ferns, Gnetophyta , Cordaitales and the Bedecktsamern . Only the discovery of seed-bearing megasporophylls in 1977, which belonged to already known representatives, made the classification of the seed ferns clear.
The spread of Glossopteris was one of the most important arguments in the early discussion about the theory of continental drift and the existence of a southern continent ( Gondwana , after Eduard Suess ).
literature
- Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants. Prentice Hall, Englewood Cliffs 1993, pp. 558-574, ISBN 0-13-651589-4
Individual evidence
- ↑ a b R.S. Hill, EM Truswell, S. McLaughlin, ME Dettmann: Evolution of the Australian Flora: Fossil evidence . In: AE Orchard (Ed.): Flora of Australia. Volume 1. Introduction . 2nd edition, ABRS / CSIRO Australia, Melbourne 1999, p. 260. ISBN 0-643-05965-2
- ↑ RE Gould, T. Delevoryas: The biology of Glossopteris : Evidence from petrified seed-bearing and pollen-bearing organs. In: Alcheringia , Volume 1, 1977, pp. 387-399.