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General characters of gymnospermic plants

Gymnosperm:-

  • Gymnosperm means naked seed. 
  • The word 'gymnosperm' is derived from Greek words- 'gymnos', means naked and 'sperma' means seed. 
  • Gymnosperm are those seed plants in which the ovules are not enclosed in ovary and the pollen typically germinate on the surface of the surface of the ovule. 
  • The term 'gymnosperm' was introduced by Theophrastus in 300 B.C.

General  character s of gymnosperms :-

  • All gymnosperm are perennial, none of them are herbs or annual. 
  • Double fertilization is absent. 
  • Pollination is of anemophilous type. 
  • Leaves are provided with thick cuticularised epidermis with waxy coating and sunken stomata. 
  • Vessel, xylem fibres and companion cells are absent in vascular tissue. 
  • Occurrence of transfusion tissue in the leaves. 
  • Ovules are not enclosed in an ovary. 
  • The reproductive organs are arranged in form of compact structures known as cones. 
  • The cones are Unisexual. 
  • Male cones are usually small and short lived than female cones. 
  • In male cones, several microsporophylls are spirally arranged on the central axis, each possessing several microsporangia containing microspores or pollen grains. 
  • Usually gymnosperm shows polyembryony, perhaps it occurs due to presence of more than one archegonia in the female gemetophyte of the ovule. 
Diversity and origin :-

  • There are over 1000 living species of gymnosperm.
  • It is widely accepted that the gymnosperms originated in the late Carboniferous period, replacing the lycopsid rainforests of the tropical region.
  • This appears to have been the result of a whole genome duplication event around 319 million years ago.
  • Early characteristics of seed plants were evident in fossil progymnosperms of the late Devonian period around 383 million years ago. It has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was by extinct species of scorpionflies that had specialized proboscis for feeding on pollination drops. 
  • The scorpionflies likely engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms.
  • Evidence has also been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct genus with members which (in an example of convergent evolution) resembled the modern butterflies that arose far later.

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