Gymnosperms are the small group of plants, which constitutes a sub division of spermatophyta or phanerogams. There are about 73 genera and 7000 species in subdivision Gymnospermae. Most of the genera are entirely extinct and only a few are living. Gymnosperms act as a connecting link between pteridophytes and angiosperms. K.R. Sporne in 1962 classified the whole gymnosperms into three classes and they are cycadopsida, coniferopsida and gnetopsida.
Characteristic of Gymnosperms
1. Vessels are absent except order Gnetales (Gnetum, Ephedra, Welwitschia). Gnetales act as connecting link between gymnosperms and angiosperms
2. Companion cells are altogether absent.
3. Reproductive organs form cones or strobilus except female organs of Cycas.
4. Ovule is generally orthrotropous, unitegmic with three layers.
5. Endosperm is formed before fertilization and is always haploid.
6. Smallest archegonium of plant kingdom is present in this group.
7. Fertilization occurs by pollen tube (siphonogamy). Double fertilization is absent.
8. Pollination is anemophilous.
9. Polyembryony is the usual feature.
10. Wood is manoxylic (soft and loose) eg., Cycas or Pycnoxylic (Compact and hard) eg., PinusRead more: Classification of Gymnosperms / Economic Importance of Gymnosperms