Oogamy

Isogamy is considered to be the most primitive and oogamy the most advanced type of sexual reproduction. The evolution from isogamy to oogamy through unisogamy is seen in different groups of the Chlorophyceae. Since oogamy has arisen quite independently in several groups, sometimes even within the limits of a single genus (e.g., Chlamydymonas), not much phylogenetic significance can be attached to it.

In the majority. motile zoospores or gametes are formed; sexual processes have evolved independently in various divisions and have included the development of oogamy.

Throughout the process of algal and plant evolution, the mode of mating has evolved from isogamy to unisogamy, and, finally, oogamy. While all three types are seen among algae, only oogamy is found among land plants.