GENERAL CHARACTERS :
- The plants shows alternation of generation. The gametophyte and sporophyte phases alternate with each other to complete the life cycle.
(a) Gametophytic Phase: It is subsidiary phase which is haploid and short lived.
(b) Sporophytic Phase: It is main phase which is diploid, long lived and occurs as a whole plant.
- Plants of this group possess naked ovule/seeds.
- Ovules are naked and not enclosed by the ovary therefore recognized as a Gymnosperm.
- Gymnosperms vary in size from small plants to very large gigantic plants.
Zamia pygmea is the smallest Gymnosperm having an underground tuberous stem (20-30 cm).
Sequoia sempervirens is the tallest tree of the world having height of about 150 m.
- Plant body is Sporophytic and differentiated into root, stem and leaves.
- Leaves are two types-
(a) Foliage leaves (Big and Green)
(b) Scaly leaves (Minute and Brown)
- The leaves may be simple or compound.
- Leaves having thick cuticles and sunken stomata.
- Plants are evergreen, perennial trees or shrubs showing xerophytic characters.
- Vascular tissues are present.
- Absence of true vessels and companion cells.
- The stems are unbranched (Cycas) or branched (Pinus, Cedrus).
- Gymnosperms show single fertilization.
- Pollination takes place through wind and formation of endosperm takes place before fertilization (pre-fertilized).
- The ovules are Orthotropous.
- True fruits are lacking because of the absence of ovary.
- Sporophylls are arranged on central axis in the form of cone or strobilus.
- Cones are unisexual and Gymnosperm are heterosporous.
- In a male cone, microsporophylls bear microsporangia which produce a large number of microspores and in female cone, megasporophyll bears megasporangia which produce four megaspores.
Note: At this point microsporophyll, microsporangia and microspores can be compared with stamen, anther and pollen grains of Angiosperms respectively. Similarly megasporophyll and megasporangia can be compared with gynoecium and ovule respectively.
- The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (Pinus). In other genera, specialised roots called coralloid roots (associated with N2-fixing Cyanobacteria in Cycas).
Eg.: Cycas, Pinus, Thuja (ornamental plant in gardan- Morpichh or Vidhya), Araucaria (Christmas tree), Bennettites (Fossil plant).