Spermatophyte
Scots pine (Pinus sylvestris)
The seed plants ( Spermatophytina ) are one of the groups in the plant kingdom. They form seed propagation as organs.
- 4.1 Notes and references
Features
The seed plants are primarily woody plants with secondary growth, herbaceous growth forms are considered to be derived. They are seeds that contain the embryo protected in maternal tissue ( seed coat ) and represent a resting stage as well as the propagation organs. The fertilization is independent among them, in contrast to mosses and ferns, entirely on water.
The sporophylls are usually grouped into flowers or cones.
Reproduction
The seed plants go through a generational change: Change It - as with ferns and mosses - sporophyte and gametophyte from. The sporophyte is the plant that is commonly known as a tree, shrub or herb. The reproductive organs are in bloom. There in the pollen sacs of the stamens, the pollen grains are produced. In the carpels, the embryo sac is formed. The male gametophyte grows from the pollen grain ( the spores of a fern equivalent ) out as a pollen tube that grows through the style to the embryo sac and there fertilizes the egg. The embryo sac is the female gametophyte dar. It forms the ovum. Both gametophyte have only half the chromosomes of the sporophyte, they are haploid.
System
Outer systematics
As the precursors of seed plants are today accepted the Progymnospermen general. There are, however, there are two main theories:
- Rothwell assumes that the monophyletic seed plants from an ancestor that matches the Aneurophytales descended.
- Beck assumes that the seed plants have emerged diphyletisch: the seed ferns would thus descended from the Aneurophytales, Cordaitales and conifers of the Archaeopteridales.
The two hypotheses can be obtained by molecular genetic studies not verify because the question precursor groups are all extinct. Molecular genetic research has shown to be the closest related group, the ferns.
Inside systematics
There are four extant groups of seed plants. The first three are grouped as gymnosperms ( gymnosperms ):
- Cycads ( Cycadopsida )
- Ginkgo plants ( Ginkgoopsida )
- Coniferopsida including Gnetales
- Angiosperms ( Magnoliopsida )
There are also the only surviving group of fossil seed ferns, however, do not form a natural kinship group. Your Paleozoic representatives convey rather between the ferns and the other seed plants, the Mesozoic representatives are discussed as a precursor to the angiosperms.
Some groups of fossil gymnosperms, plants can no large group be assigned closer:
- Gigantopteridales
- Vojnovskyales
- Czekanowskiales
- Iraniales
- Pentoxylales
- Hermanophytales
- Dirhopalostachyaceae
- Cordaitales
About the phylogenetic relationships within the seed plants are in disagreement. We discuss four ways, in essence, the Anthophyten hypothesis the least support obtained by molecular biological studies. The hypotheses differ mainly by the different position of Gnetophyta in the pedigree. They come partly lie even within the conifers, so that they would then be paraphyletic.
The Anthophyten hypothesis:
Conifers (without Pinaceae )
Pinaceae
Ginkgo
Cycadophyta
Gnetales
Angiosperms
The Gnetales as the sister group of the angiosperms are often the result of phylogenetic studies based on morphological characteristics, which often also include fossil representatives. Molecular genetic studies contradict the generally.
The Gnetales - sister hypothesis ( Gnetales as the sister group of all other seed plants ):
Conifers (without Pinaceae )
Pinaceae
Ginkgo
Cycadophyta
Angiosperms
Gnetales
The Gnetifer hypothesis ( Gnetales as the sister group of conifers):
Conifers (without Pinaceae )
Pinaceae
Gnetales
Ginkgo
Cycadophyta
Angiosperms
The Gnepine hypothesis ( Gnetales as a sister group to Pinaceae ):
Gnetales
Pinaceae
Conifers (without Pinaceae )
Ginkgo
Cycadophyta
Angiosperms
The Gnetales as a sister group to Pinaceae is a fairly common result of molecular genetic studies. This result has been cited by other sources, that the Gnetales hardly can be derived from modern conifers and the molecular genetic results are distorted by the non- inclusion of many extinct groups.
Recent works show as a further option the Gnetales as the sister group of conifers (without Pinaceae ).
Documents
- Peter Sitte, Elmar Weiler, Joachim W. Kadereit, Andreas Bresinsky, Christian Körner: textbook of botany for colleges. Founded by Eduard Strasburger. 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010- X, pp. 750-783.