General characteristic features of Gymnosperms

General characteristic features

•            Most of the gymnosperms are evergreen woody trees or shrubs. Some are lianas (Gnetum)

•            The plant body is sporophyte and is differentiated into root, stem and leaves.

•            A well developed tap root system is present. Coralloid Roots of Cycas have symbiotic association with blue green algae. In Pinus the roots have mycorrhizae.

•            The stem is aerial, erect and branched or unbranched (Cycas) with leaf scars.

•            In conifers two types of branches namely branches of limited growth (Dwarf shoot) and Branches of unlimited growth (Long shoot) is present.

•            Leaves are dimorphic, foliage and scale leaves are present. Foliage leaves are green, photosynthetic and borne on branches of limited growth. They show xerophytic features.

•            The xylem consists of tracheids but in Gnetum and Ephedra Vessels are present­.

•            Secondary growth is present. The wood may be Manoxylic (Porous, soft, more parenchyma with wide medullary ray -Cycas) or Pycnoxylic (compact with narrow medullary ray-Pinus).

•            They are heterosporous. The plant may be monoecious (Pinus) or dioecious (Cycas).

•            Microsporangia and Megasporangia are produced on Microsporophyll and Megasporophyll respectively.

•            Male and female cones are produced.

•            Anemophilous pollination is present.

•            Fertilization is siphonogamous and pollen tube helps in the transfer of male nuclei.

•            Polyembryony  (presence  of  many embryo)­ is Present. The naked ovule develops into seed. The endosperm is haploid and develop before fertilization.

•            The life cycle shows alternation of generation. The sporophytic phase is dominant and gametophytic phase is highly reduced. The photograph of some of the Gymnosperms is given in Figure 2.38