Naked seed plants
The Nacktsamigen plants (gymnosperms, from ancient Greek γυμνός Gymnos "naked" and σπέρμα sperm "germ", "seed" - literally "naked seed"), short gymnosperms are in the subdivision Coniferophytina with classes Ginkgoatae and Pinatae and the subdivision Cycadophytina with divided into the classes Cycadatae and Gnetalae . The seed ferns form the class Lyginopteridatae .
The gymnosperms are seed plants (spermatophytina) whose ovules not, as in the flowering plant in an ovary are included. The carpels are unlike angiosperms , not closed (angiosperms) completely. This represents the original state within the seed plants.
Since the Upper Permian , 270 million years ago (270 Ma ), the groups of naked samers developed. Later, in the Middle Cretaceous , 120 million years ago, the Bedecktsamer developed (individual precursors are already known from the Upper Jurassic ). All bare-seeded taxa are now relic groups . Compared to the hundreds of thousands of species there are now only a good five hundred species. Even the higher taxa like classes often contain only a few species. The areas are often disjoint , which also shows that these groups are only relics. The Nacktsamer had the peak of their development with most of the species in the Jura, they served, among other things, as food for many dinosaurs . Today the coniferous plants (Pinophyta) are rich in species and are widespread, with over 350 species. Fossil finds give a small overview of the earlier biodiversity of the naked-seed taxa and the ecosystems that formed them at that time.
All of today's naked plants are woody plants with secondary growth in thickness . Of the angiosperms , the gymnosperms plants differ in the arrangement of their pathways . In addition, in contrast to the flowering plants, they only have tracheids in the xylem. Furthermore, the ovules of angiosperms of carpels included (carpels) and the seed is spread by a fruit.
The flowers are separate sexes and consist only of micro- and megasporophylls (the terms stamens or carpels should be limited to the bedecktsamer). Many flowers of one sex are often grouped together in cones . Gymnosperms are usually monoecious ( monoecious ), but there are also dioecious ( dioecious ) species. The pollen is mostly spread with the help of the wind ( anemophilia ). But insect pollination was also observed. Then the pollen reaches the unprotected micropyle , the point of conception. In ginkgo plants (Ginkgophyta) and cycads (Cycadophyta) there are flagellated sperm cells (spermatozoids), similar to many algae . These are released from the pollen tube into a liquid-filled depression at the vertex of the nucellus (pollen chamber) so that they can swim to the egg cell. In the other groups, the pollen tube grows to the egg cell , where it releases a gamete nucleus that fertilizes the egg cell. There is only a short path without barriers between pollination and fertilization . However, a lot of time can pass between the two processes.
- Cycads (Cycadopsida): with around 200 to 300 species
- Ginkgo plants (Ginkgoopsida): with only one recent species
- Softwood family (Pinophyta or Coniferopsida ): with around 600 to 630 species
- Gnetophyta : with about 69 to 81 species
Welwitschia mirabilis , Gnetophyta
Ephedra distachya , Gnetophyta
Ginkgo biloba , Ginkgo plants (Ginkgophyta),
twig with leaves
- Gymnosperms - Chapter from "Botany online", an Internet hypertext book from the Department of Biology at the University of Hamburg
- Information on all taxa within the gymnosperms (Engl.)
- A. Bresinsky, Ch. Körner, JW Kadereit, G. Neuhaus, U. Sonnewald: Strasburger - Textbook of Botany . 36th edition, Spektrum Akademischer Verlag, Heidelberg 2008, p. 833. ISBN 978-3-8274-1455-7