• Origin: zygotic embryos are the result
  of the fusion of gametic cells, which
  results in the formation of a zygote;
  for somatic embryos (syn. asexual
  embryos) fusion is not required.
• Morphology: a fully developed embryo
  is a bipolar axis with a shoot meristem
  on the one end and a root meristem
  on the other one; it is also characterized
  by a special type of leaves, the cotyledons.
• Evolution: embryo development is
  characterized by a succession of typical
  morphological stages (globular, heart
  shaped and torpedo shaped)

Typical morphological
stages during embryo
development: (A) globular,
(B) heart shaped, (C) torpedo