Lyginopteridales

Crossotheca, pollen organ

The Lyginopteridales are a Paleozoic order of extinct group of plants the seed ferns. The group is relatively poorly known until today, but they played an important role in the history of science in identifying the group of seed ferns.

The Lyginopteridales are a heterogeneous and probably artificial grouping. Common features that are found in most representatives, the structure of the stele and the presence of sclerenchyma in the cortex. The stelae represent transitional forms from those of Calamopityales to real Eustelen dar. younger forms have increasingly more parenchyma. The early seed ferns such as the Lyginopteridales expected from Progymnospermen, about the Aneurophytales, have emerged.

Lyginopteris

Vegetative characteristics

Lyginopteris has Stems with up to 4 cm in diameter. The shoot axis is a Eustele, it has a central, parenchymatous marrow, in which scattered nests of sclerotic cells are located. To the marrow of five to ten primary xylem strands are arranged. The xylem is mesarch, the tracheids of Metaxylems have vielreihige wells. The amount of secondary xylem is relatively modest compared to the diameter of the tree. The secondary xylem consists of tracheids with large square -rimmed pits in their radial walls. In some instances, a small amount of secondary xylem is on the Mark- side, so there was a second cambium, xylem formed towards the inside. Well-preserved strains possess thin-walled cells at the site topographically corresponding to the phloem sieve plates, however, were not observed. At the phloem to the outside a zone of cells follows, which are interpreted as pericycle, and are embedded in the co- sclerotic cells. Outwardly, followed by a periderm. The bark is separated into two zones: the inside is rarely obtained, and consists mainly of parenchyma, the outer bark is relatively wide, including the parenchyma, and radially arranged fiber ribbons which extend in the longitudinal direction over the trunk. These bands anastomose reticulate.

In young stems of Lyginopteris numerous multicellular glands are observed in the epidermis, which can also be found on all the other parts of the plant except the root. The glands are about 3 mm long, have a broad base and a glandular head. Lolly's gland are stomata. The epidermis of the distal end is composed of tubular cells surrounding secretory tissue.

The leaf traces are caused by a tangential division of a strand of primary xylem. In the bark splits the leaf-trace to reunite in the base of the petiole. The resulting beam has a V- or W -shape. Petioles with this anatomy are placed in the form genus Lyginorachis. The leaves are in a 2/5-Anordnung, the individual leaves branch forked below the lowermost pinnae. The lateral leaflets are opposite or nearly opposite, the large fronds is striking in two dimensions. The leaflets correspond to the shape genus Sphenopteris. They are arranged lobed and alternate.

The roots are adventitious. They arise on all sides of the stem, sometimes in vertical rows. You are triarch to polyarch and possess secondary xylem. The roots of Lyginopteris are often performed as a form genus Kaloxylon.

Seed organs

The seed organs of Lyginopteris are - if they are obtained as mineralized fossils - known as Lagenostoma. The ovule is ellipsoidal with a length of approximately 5.5 mm and a width of up to 4.2 mm. The integument is made of thick-walled cells in two layers, the inner cells are stretched in the longitudinal axis of the ovule, the outer radially oriented. On Mikropylen end the integument forms a cap of nine lobes, which are supplied by a vascular bundles each. The thick-walled cells are covered by a narrow, thin-walled parenchyma, which is, however, fossil usually not obtained.

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 ( Lagenostom ), the relatively loosely surrounding a parenchymatous central column. The Lagenostom probably have overlapped the Integumentlappen. The central column could have played a role in the production of a pollination drop or otherwise in the forwarding of the pollen grains to the archegonia. The structure is also interpreted to the effect that pollen was included in the pollen chamber. In well-preserved specimens is the Megagametophyt, surrounded by a thin spore wall to recognize. It is differentiated into an outer region of elongated cells and an inner region of isodiametric cells. Near the distal end are up to three archegonia, lacking the neck cells.

The ovules were seated individually in cupulae. If they are found without ovules, they are in the form genus Calymmathotheca. The cupula is tulip-shaped, consisting of several lobes that are fused at the bottom and are wrinkled on the outside. The outside bears the characteristic of Lyginopteris kopfchentragenden glands. The lobes are supplied by each one vascular bundles. The seeds are very often alone, without cupula, found, therefore it is assumed that they were fired to maturity of the cupula. The cupulae sit at the ends of branched axes, respectively.

Pollen organs

There are no pollen organs known that Lyginopteris can be assigned unambiguously. Crossotheca is often used as the pollen organ considered, but only because of the connection to the leaves Sphenopteris and the stratigraphic occurrence. However, it is interpreted as eusporangiater fern. It consists of pinnate leaves whose leaflets are fertile and arrow-shaped. At the bottom sit up 30 per 4 mm long sporangia. The pollen grains have a diameter of 70 microns and are trilet ( have a three-rayed scar ). Sitting at the base of the pinnules pinnate leaves of the type Pecopteris or Sphenopteris.

Feraxotheca could be another form of conservation Crossotheca. The axes are branched here three times, the leaflets of the last order are alternate. The leaflets are greatly reduced, sit on a pillow parenchymatous 6-10 together pressed, elongated sporangia. The center of the Synangiums is hollow, in this cavity was the emptying of the sporangia. The pollen grains are 40 to 60 microns in size, trilet and studded with small cones. Sterile pinnules at Feraxotheca culcitaus are lobed and have dichotomously branched vascular bundles.

More ordinary genera

Several other master classes will be provided to Lyginopteridales.

• Heterangium Lyginopteris similar, but occurs in North America and Europe. The stems have a diameter of 2 cm and are little branched. They have a protostele consisting of tracheids bundles and parenchyma. In Heterangium grievi go large metaxylem tracheids - over at the periphery into smaller, tracheids, which are around 20 mesarchen Xylemsträngen. To this primary xylem there is a band secondary xylem. In many Heterangium strains, the phloem is obtained. Heterangium americanum has primary and secondary phloem: the primary are small groups of cells at the periphery of the secondary. This is highly developed and exceeds the xylem in width. It consists of elongated sieve, phloem parenchyma and Phloemstrahlen who continue the Xylemstrahlen. The bark of Heterangium is divided into two: the inner zone consists of the parenchyma with uniformly distributed plates of thick-walled cells, the exterior of longitudinally oriented fibers embedded in a parenchyma. The leaves belong to Sphenopteris type. Finds from the Upper Mississippian have branched petioles and leaves of rhodea type: they do not have flat leaf blade, the ends of the leaflets consist of dichotomously branched, sterile segments.
• Microspermopteris is known from North America and Germany. The small tribes have a pentarche protostele, the metaxylem wedges are separated by radially arranged Parenchymplatten. The protoxylem is located on the sides of Parenchymplatten on the edge of the xylem. In the thicker stems, there are secondary xylem. The leaves are in 2/5-Phyllotaxis and have large, stem comprehensive, V -shaped leaf bases. The leaves belong to Sphenopteris type. The roots are triarch and perhaps also had secondary xylem. Adventitious roots are frequently observed.
• In Schopfiastrum from the Middle Pennsylvanian, the primary xylem of two to four protoxylem strands that are surrounded by metaxylem. The latter consists of large tracheids and a few scattered parenchymal cells. The protostele is oval in cross section. The secondary xylem is wide and has wooden beams. The inner bark and the phloem -rich large channels of 1 mm in diameter that are filled with an amber material which is held by many authors for the resin. In the outer cortex, there are longitudinal sclerenchyma fibers.
• Genera from the Lower Carboniferous, which are assigned to Lyginopteridales are Rhetinangium, Tetrastichia with cross-shaped and triangular Tristichia protostele.
• Pitys, also from the Lower Carboniferous, is a genus with several species of large forest trees with partly over a meter in diameter. Belonging to the order, however, is very uncertain, as is the Eristophyton of 25 cm diameter and Stanwoodia.

Other seeds and cupulae

The number of seeds forms which are assigned to the Lyginopteridales is substantially greater than that of the parent forms. However, it has been found out Lagenostoma in physical connection with other organs no seed forms.

• Sphaerostoma oval from the Lower Carboniferous of Scotland is considered to Heterangium grievii. The ovules are about 2.5 mm long, the integument has three layers with a fibrous middle layer ( Sklerotesta ). 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, which terminate at the top in free flap. Pollen chamber and Lagenostom are similar to Lagenostoma. The found in the seeds of plants pollen is large with 104 microns.
• Conostoma includes a number of species from the Upper Carboniferous of Europe and North America. The seeds are radial symmetry with a maximum of one centimeter in diameter. The Lagenostom is toroidally. Conostoma kestospermum has an unusual integument. The Sklerotesta consists of two zones: the cells of the outer zone are perpendicular to the longitudinal axis and form distinct, irregular bands that run around the seed.
• Other seeds are Coronostoma, Physostoma, Calathosperma and Gnetopsis.

More pollen organs

Pollen organs are much less well known than the seeds. Besides Crossotheca / Feraxotheca there is a second type of pollen organs: in Telangium and '' Telangiopsis that first appear in the Upper Tournaisian, sit the pollen organs of monopodial branched structures that may replace a portion of a vegetative frond or the whole frond. Telangium scottii is widely used in the UK and consists of 1.7 mm long synangia of eight thick-walled, basal fused sporangia. Telangium fossils from Illinois consist of eight radially arranged sporangia that form a cup-shaped Synangium with a parenchymatous center. Telangiopsis Telangium resemble, but are obtained as compression fossils. The Sporangiengruppen at the ends of dichotomous or monopodial branched axes that do not have leaf blades.

The younger Phacelotheca from Scotland sitting on stems, at Mellissiotheca, also from Scotland, there is a Synangium from 50 to 150 sporangia in a parenchymatous cushion. Your similar Schopfiangium from North America.

Dichotangium quadrothecum from the Lower Carboniferous consists of istom branched twigs, other peaks are synangia, the flat structures of 12 or 24 unfused sporangia are. A sporangium is about 2 mm long tip sharpened. These structures are associated with the fronds of Diplopteridium holdenii, consisting of two to three times forked fronds. The leaflets are slashed flat and strong.

Early pollen organs such Telangium are very similar to those of Progymnospermen. The development of the Progymnospermen sporangia to Telangium can be considered the formation of a flat frond structure that supports their synangia on the underside of leaves, are interpreted.

Botanical history

The presence of the characteristic glands at all plant organs of Lyginopteris has allowed Oliver and Scott, 1904, to reconstruct from individual parts, the whole plant. Thus the existence of the seed ferns was established.

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.