Many systems of classification of Gymnosperms have been proposed by different authors. According to the Classification of Sporne (1965), Gymnosperms are classified into three classes. Among them, Gnetopsida is the third one.
In this article, the only order of Gnetopsida is discussed in detail.
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The Order Gnetales is considered as the most advanced group among gymnosperm.
Gnetales is represented by three families, viz. Gnetaceae, Ephedraceae and Welwitchiaceae.
Characteristic features of gnetales
- Plants are usually shrubs, lianas, sometimes trees.
- Leaves are spirally arranged, opposite or whorled.
- Leaves are simple, may be scale-like, strap-shaped or sometimes ovate to elliptic.
- Vessels are found in xylem.
- Companion cells present in phloem.
- No resin canals found.
- Flowers unisexual.
- Male flowers are surrounded by sterile perianth scales.
- Ovule is surrounded by extra envelops.
- The sporangiophores in the male flowers have 1-8 synangia.
- Pollen grains are devoid of wings.
- Embryo has two cotyledons.
- The inner integument of the ovule is produced into a long and tube-like micropyle.
e.g. Gnetum oblongum
(Discussion about the families of gnetales will be added later…)
Class Lecture of Dr. M. Oliur Rahman,
Department of Botany, University of Dhaka.