The pollen grains and spores constitute an important morphological entity, reflecting the facts and facets of plant evolution. Among the various characters of the exine, the aperture is considered to be the most conservative. The grains are primorphous (apertures indistinct) in Thallophyta, trimorphous (trilete, monolete and alete) in Archegoniatae and polymorphous (colpate, colporate, porate, etc., the apertures varying in number and form), in the angiosperms. The trimorphous condition is characteristic of the preangiospermous Archegoniatae, and its occurrence in the angiosperms may be considered to provide an indication of the primitive taxa of the group. Against this background, it is argued that the angiosperms are triphyletic, having three independent phylogenetic stocks, namely the Monocot stock, the Magnolian dicot stock, and the Ranalean dicot stock, in that order of phylogenetic succession