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.
(c) 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.
(c) They possess an aromatic, antiseptic semi fluid resin.
(d) Conifers mostly occur in colder region, e.g.,Pinus, Cedrus, Juniperus, Picea etc.
(a) This group includes climbing shrubs and small trees.
(b) Their xylem possess vessels.
(c) The reproduction organs are borne in whorls or inflorescence.