What are the main classes of gymnosperms ? Briefly mention their properties

Gymnosperms include three main classes :

  1. Cycadopsida (Cycads):
    (a) Cycades constitute a small group of gymnosperms with palm like habit and fern like foliage.
    (b) Cycades are mostly xerophytic and occur in warm regions.
    © They are also grown as ornamental plants e.g.,Cycas.
    (2) Coniferopsida (Conifers):
    (a) Conifers are the dominant gymnosperms including more than 500 living species
    (b) They are cone bearing plants with excurrent habit or conical canopy.
    © They possess an aromatic, antiseptic semi fluid resin.
    (d) Conifers mostly occur in colder region, e.g.,Pinus, Cedrus, Juniperus, Picea etc.
    (3) Gnetopsida:
    (a) This group includes climbing shrubs and small trees.
    (b) Their xylem possess vessels.
    © The reproduction organs are borne in whorls or inflorescence.