Linked from
The 7 pages that link to Oogamy, each with the reason it gives.
ArchegoniumRelated: The archegonium protects the large egg characteristic of oogamy.
Brown algaeRelated: Oogamy is common among brown algae, including kelps.
CharophytaRelated: Oogamy occurs in stoneworts and other complex charophytes.
Yellow-green algaeRelated: This reproductive pattern occurs in some members of the group.