Lyginopteridales
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Crossotheca , pollen organ |
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The Lyginopteridales are a Paleozoic order of the extinct plant group of seed ferns . The group is relatively poorly known to this day, but it played an important role in the history of science in recognizing the group of seed ferns.
The Lyginopteridales are a heterogeneous and arguably an artificial group. Common features that appear in most of the representatives are the structure of the stele and the presence of sclerenchyme in the cortex . The steles are transitional forms from those of the Calamopityales to real Eusteles. Younger forms increasingly have more parenchyma . The early seed ferns like the Lyginopteridales are likely to have emerged from progymnosperms such as the Aneurophytales .
Lyginopteris
Vegetative characteristics
Lyginopteris has shoot axes up to 4 cm in diameter. The stem axis is a eustele , it has a central, parenchymatic marrow in which there are scattered nests of sclerotic cells. Five to ten primary xylem strands are arranged around the medulla . The xylem is mesarch, the tracheids of the metaxylem have multi-row pits. The amount of secondary xylem is relatively modest compared to the stem diameter. The secondary xylem consists of large tracheids with angular pits in the radial walls. In some specimens there is a small amount of secondary xylem on the pith side, so there was a second cambium that formed xylem on the inside. Well-preserved strains have thin-walled cells at the topographically corresponding point of the phloem , but sieve plates were not observed. On the outside of the phloem, there is a zone of cells that are interpreted as a pericycle , and in which sclerotic cells are also embedded. A periderm connects to the outside . The cortex is divided into two zones: the inner one is seldom preserved and consists mainly of parenchyma, the outer cortex is relatively wide, includes parenchyma and radially arranged fiber bands that extend longitudinally over the trunk. These ligaments anastomose like a network.
In young strains of Lyginopteris numerous multicellular glands can be observed on the epidermis , which can also be found on all other parts of the plant with the exception of the roots. The glands are around 3 mm long, have a broad base and a glandular head. There are stomata on the stalk of the gland . The epidermis at the distal end consists of tubular cells that surround a secretory tissue.
The leaf marks are created by a tangential division of a strand of the primary xylem. In the bark, the leaf trail divides to reunite in the base of the petiole . The resulting bundle has a V or W shape. Petioles with this anatomy are placed in the genus Lyginorachis . The leaves are in a 2/5 arrangement , the individual leaves branch out in a bifurcated manner below the lowest pinna. The side feathers are opposite or almost opposite, the large frond is conspicuously two-dimensional. The leaflets correspond to the genus Sphenopteris . They are lobed and arranged alternately.
The roots are adventitious roots . They arise on all sides of the trunk, sometimes in vertical rows. They are triarch to polyarch and have secondary xylem. The roots of Lyginopteris are often listed as the genus Kaloxylon .
Seed organs
The seed organs of Lyginopteris - provided they are preserved as mineralized fossils - are known as ply ostomas . The ovule is ellipsoidal with a length of around 5.5 mm and a width of up to 4.2 mm. The integument consists of thick-walled cells in two layers: the inner cells are stretched in the longitudinal axis of the ovule, the outer ones are oriented radially. At the micropylene end, the integument forms a cap made of nine lobes, each of which is supplied by a vascular bundle . The thick-walled cells are covered by a narrow, thin-walled parenchyma , which is mostly not fossilized.
The inner part of the integument is fused with the nucellus , with the exception of the distal end. Here the nucellus has a bottle-shaped structure (lagenostome), which relatively loosely surrounds a parenchymal central column. The positional ostome may have protruded beyond the integument flaps. The central column could have played a role in the production of a pollination drop or otherwise in the transmission of the pollen grains to the archegonia . The structure is also interpreted to mean that pollen was trapped in the pollen chamber. The megagametophyte , surrounded by a thin wall of spores, can be seen in well-preserved specimens . It is differentiated into an outer area made up of elongated cells and an inner area made up of isodiametric cells. Up to three archegonia are located near the distal end, lacking neck cells.
The ovules sat individually in cupules . If they are found without ovules, they are assigned to the genus Calymmathotheca . The cupula is tulip-shaped, consists of several lobes that are fused in the lower area and are wrinkled on the outside. The outside bears the head-bearing glands characteristic of Lyginopteris . The lobes are each supplied by a vascular bundle. The seeds are very often found alone, with no cupula, so it is believed that they were released from the cupula at maturity. The cupules sit at the ends of branched axes.
Pollen organs
There are no known pollen organs that can be clearly assigned to Lyginopteris . Crossotheca is often viewed as the pollen organ, but only because of its connection to the leaves of Sphenopteris and the stratigraphic occurrence. But it is also interpreted as a eusporangiate fern . It consists of pinnate leaves, the leaflets of which are fertile and arrow-shaped. On the underside are up to 30 sporangia, each 4 mm long . The pollen grains have a diameter of 70 micrometers and are trilet (have a three-pointed stigma). Feathers of the Pecopteris or Sphenopteris type sit at the base of the leaflets .
Feraxotheca could be another form of conservation of Crossotheca . The axes are threefold branched here, the last-order pinnacles are alternate. The leaflets are greatly reduced; 6 to 10 elongated sporangia are pressed together on a parenchymatic cushion. The center of the synangium is hollow, in this cavity the emptying of the sporangia took place. The pollen grains are 40 to 60 micrometers in size, trilobed and covered with small cones. Sterile leaflets in Feraxotheca culcitaus are lobed and have dichotomously branched vascular bundles.
Further trunk genera
Several other genus strains are added to the Lyginopteridales.
- Heterangium is similar to Lyginopteris , but is found in North America and Europe. The trunks have a diameter of 2 cm and are not very branched. They have a protostele , which consists of tracheid bundles and parenchyma. In Heterangium grievi , large metaxylem tracheids turn into smaller tracheids on the periphery, which are in around 20 mesaric xylem strands. Around this primary xylem there is a band of secondary xylems. Many Heterangium strains that is phloem get. Heterangium americanum has primary and secondary phloem: the primary are small groups of cells on the edge of the secondary. This is strongly developed and exceeds the xylem in width. It consists of elongated sieve cells , phloem parenchyma , and phloem rays that continue the xylem rays. The cortex of heterangium is divided into two parts: the inner zone consists of parenchyma with evenly distributed plates of thick-walled cells, the outer zone consists of longitudinally oriented fibers embedded in a parenchyma. The leaves belong to the Sphenopteris type. Finds from the Upper Mississippium have branched petioles and leaves of the Rhodean type: they do not have a flat leaf blade, the ends of the pinna consist of dichotomously branched, sterile segments.
- Microspermopteris is known from North America and Germany. The small stems have a pentarch protostele, the metaxylem wedges being separated by radially arranged parenchymal plates. The protoxylem is located on the sides of the parenchymal plates on the edge of the xylem. There is secondary xylem in the thicker stems. The leaves are in 2/5 phyllotaxis and have large, stem-encompassing, V-shaped leaf bases. The leaves belong to the Sphenopteris type. The roots are triarch and may also have had secondary xylem. Adventitious roots can often be observed.
- In Middle Pennsylvanian Schopfiastrum , the primary xylem consists of two to four protoxylem strands surrounded by the metaxylem. The latter consists of large tracheids and a few, scattered parenchymal cells. The protostele is oval in cross section. The secondary xylem is broad and has wood rays . Large channels 1 mm in diameter extend through the inner bark and phloem and are filled with an amber-colored material that some authors believe to be resin . In the outer cortex there are longitudinal sclerenchymal fibers.
- Genera from the Lower Carboniferous, which are assigned to the Lyginopteridales, are Rhetinangium , Tetrastichia with a cruciform and Tristichia with a triangular protostele.
- Pitys , also from the Lower Carboniferous, is a genus with several species of large forest trees, some of which are over a meter in diameter. Belonging to the order is, however, very uncertain, as is that of Eristophyton with 25 cm in diameter and Stanwoodia .
More seeds and cupules
The number of seed forms that are assigned to the Lyginopteridales is much greater than that of the stem forms. Except for the positional ostoma , however, none of the seminal forms has been found to be physically associated with any other organ.
- Sphaerostoma ovale from the Lower Carboniferous Scotland is considered to be part of Heterangium grievii . The ovules are around 2.5 mm long, the integument is three-layered with a fibrous middle layer (sclerotesta). The ovule is tightly enclosed by the cupula.
- Salpingostoma dasu from the volcanic ash of Oxroad Bay (Scotland) is up to 5 cm long with a diameter of 6 mm. The integument has six longitudinal ribs that end in free lobes at the tip. The pollen chamber and Lagenostom are similar to the Lagenostoma . The pollen found in the ovules is 104 micrometers in size.
- Conostoma includes several species from the Upper Carboniferous of Europe and North America. The seeds are radial symmetry with a maximum diameter of one centimeter. The position ostome is toroidal. Conostoma kestospermum has an unusual integument. The sclerotesta consists of two zones: the cells of the outer zone are perpendicular to the longitudinal axis and form pronounced, irregular bands that run around the seed.
- Other seeds are Coronostoma , Physostoma , Calathosperma and Gnetopsis .
Other pollen organs
Pollen organs are much less well known than the seeds. Besides Crossotheca / Feraxotheca there is a second type of pollen organs: at Telangium and Telangiopsis that in the Upper Tournaisium first occur pollen organs sit at monopodial branched structures that may replace a portion of a vegetative frond or all Wedel. Telangium scottii is widespread in Great Britain and consists of 1.7 mm long synangia of eight thick-walled, basal fused sporangia. Telangium -Fossilien from Illinois consist of eight radially disposed sporangia form a cup-shaped synangium with a parenchymatous center. Telangiopsis similar Telangium , but are obtained as compression fossils. The sporangia groups are at the ends of dichotomous or monopodial branched axes that have no leaf blades.
The younger Phacelotheca from Scotland sit on stems, in Mellissiotheca , also from Scotland, the synangium consists of 50 to 150 sporangia in a parenchymal pad. You resemble crested giangium from North America.
Dichotangium quadrothecum from the lower carbon consists of istomic branched branches, other tips are synangiae, which are flat structures of 12 or 24 non-fused sporangia. A sporangium is around 2 mm long with a pointed end. These structures are assigned to the leaf fronds of Diplopteridium holdenii , which consists of double to triple forked fronds. The leaflets are flat and severely slashed.
Early pollen organs such as telangium are very similar to those found in progymnosperms . The development from the progymnosperm sporangia to telangium can be interpreted as the formation of a flat frond structure with its synangia on the underside of the leaf.
Botanical history
The presence of the characteristic glands on all Lyginopteris plant organs made it possible for Oliver and Scott in 1904 to reconstruct the entire plant from individual parts. This established the existence of the seed ferns .
supporting documents
- Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants . Prentice Hall, Englewood Cliffs 1993, ISBN 0-13-651589-4 , pp. 494-522.
