Bennettitales

Flower -like structure

Worldwide

The Bennettitales are an extinct group of seed plants. They lived in the Mesozoic and formed flower- like structures. In her traits they resemble the one the cycads, but on the other hand the angiosperms and the Gnetales. They will be discussed as one of several possible precursors of angiosperms.

Features

Stems

The Stems are often stocky and often pachycaul. The habit of the plant, however, ranging from short and stocky to slender branches and strong. The branch acts mostly dichotomous.

The trunk is a Eustele with a strong cord. The bark is also highly trained. The wood is relatively narrow. The family of occurring in otherwise similar cycads belt of leaf traces missing.

In the secondary xylem are slim Leitertracheiden, rarely Tüpfeltracheiden. The Rays are uni- or biseriat. In the basic tissues are long resin channels.

The sheets are available in the Bennettitales to the log ends as Schopf of fronds. The leaves are morphologically very similar to those of extant cycads. In contrast to these, the stomata are syndetocheilisch formed. There are here two equatorial stationary subsidiary cells which are the same length as the guard cells. Both side as guard cells arise from a common parent cell, a form of education that is rare and about still occurs in the Welwitschia. In most plants, secondary and guard cells arise from different cells.

Young leaves are rolled ( circinate Verna Transportation ). The leaves are usually simply pinnate, rarely ungefiedert or bipinnate. Feathered double are about Banatozamites, Coreanophyllum and Nipponoptilophyllum. The nerve endings are often open, more rarely closed. Several known only as leaf fossils forms are counted among the Bennettitales due to stomatal anatomy: the most common are Nilssoniopteris, Pseudocycas, Dictyozamites, Ptilophyllum, Pterophyllum, and Otozamites Zamites. Leaves are rarely get anatomically, an example is Otozamites mortonii, feathery leaves of which form vascular bundles in the rachis in cross section omega- shaped system. Each vascular bundle is surrounded by a sclerenchyma sheath.

The Bennettitales possess not only the foliage leaves scale-like leaves that Cataphylle. Two generic names for these are Deltolepis and Cycadolepis.

Reproductive organs

The reproductive organs are in small to medium sized, hermaphrodite ( bisporangiaten ) or unisexual ( monosporangiaten ) peg-like short shoots, which are often referred to as bloom.

The axis of the pin is short, has a determined ( limited) growth and is referred to as Receptaculum. The receptaculum is cylindrical, conical or kuppfelförmig. Anatomically, it is a Eustele with a large marrow. From the Eustele branch leaf traces from in schraubiger arrangement. You can also stand so close that no arrangement can be seen.

In bisporangiaten pin the Mikrosporophylle are at the base of Receptaculums and are pinnate or fleshy. Distal are the ovules between sterile Interseminal - shed. In each bract or microsporophyll draw several leaf traces. In the distal region where the ovules begin to branch and merge the leaf traces. In each Megasporophyll or Interseminal Scale attracts only a single, circular in cross-section blade tracking. Although each ovule is surrounded by several Interseminal shed, they form no particular structure as a cupula.

Microsporangia

The pollen -forming organs are whorled, are free or fused, pinnate or simple. They carry numerous microsporangia. Several sporangia are fused ( Synangium ). In addition to some clearly attributable to Bennettitales microsporangia, there are also some isolated microsporangia found ( Morphotaxa ) that are often assigned to the Bennettitales, due to their conservation status and isolated occurrence but are not clearly assigned as Legumimanthus.

Ovules

The ovules are individually upright at the end of reduced, narrow sporophylls. The sporophyll consists of a circular Xylemstrang, which is surrounded by several layers of thin-walled cells.

The ovule is radial symmetry in cross-section: circular at William and Sonia Cycadeoidella, square up in a star pattern Cycadeoidea. The ovule tapers to a narrow, round Mikropylen opening. This may, depending on the type extend over the tops of the surrounding Interseminal shed or not.

The ovule is oriented orthotropic and has a single, several cell layers thick integument, which has no vascular bundles. The inner epidermis of the integument is near the micropyle of radially elongated cells below it are rounded or angular. The nucellus already separated at the base of the ovule integument from. It is powered by a cup-shaped bundles of tracheids, which also represents the end of the vascular tissue of the stem. The tip of the nucellus forms a cylindrical- conical plug parenchyma. This hugs the Mikropylen channel, there is, unlike virtually all gymnosperms including Gnetales, no pollen chamber. In the tissue of the nucellus megagametophytes can be seen in many fossil specimens, as an embryo. The latter has two cotyledons.

Ecology

There are numerous indications that the pollination was targeted by insects. The resinous synangia in the pollen cones of Weltrichia be interpreted as a kind of lure. In several types of Cycadeoidea coproliths found in the journal.

Spatial and temporal distribution

Fossils of Bennettitales are from the Triassic to the Cretaceous and were found on both the northern and the southern hemisphere.

Evolution and systematics

The systematic position of the Bennettitales within the seed plants is not clear. Any such requests in the past due to the very similar vegetative characteristics often in the vicinity of the Cycads ( Cycadales ), they were seen in the work of Arber and Perkin in 1907 in connection with the origin of angiosperms. See Virtually all comprehensive phylogenetic studies Bennettitales together with the Gnetales and angiosperms. This group is referred to as Anthophyten. Molecular genetic studies that did not include forced the fossil Bennettitales, but the Gnetales and angiosperms show virtually never in a common clade.

The order Bennettitales is now divided into two families:

• Cycadeoidaceae have bisporangiate journal
• Williamsoniaceae have monosporangiate cones that on a plant ( monoecious ) or on different plants ( dioecious ) sit.

Documents

• Gar W. Rothwell, William L. CREPET, Ruth A. Stockey: Is the anthophyte hypothesis alive and well? New evidence from the reproductive structures of Bennettitales. American Journal of Botany, Volume 96, 2009, pp. 296-322. doi: 10.3732/ajb.0800209
• 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. 722-741