What are trends of the gametophyte in the evolution of plants?

The tendency of the gametophyte evolution in plants has been towards the formation of gametes that are self-determining from water. In the bryophytes and in the pteridophytes the fecundation is totally dependent on water. In the phanerogamic plants such dependency doesn't exist.

An additional tendency is the reduction in the size and duration of the gametophyte.

In the bryophytes gametophyte is indeed the lasting stage. In gymnosperms, pteridophytes and angiosperms it became the temporary stage and its relative size was successively reduced.

A third evolutionary trend that is relates to the interdependency between gametophytes and sporophytes. In the bryophytes the sporophyte is completely dependent on the gametophyte to survive. In remaining plants the sporophyte is the independent stage and the once autotrophic gametophyte in the bryophytes and the pteridophytes became dependent upon the sporophyte in the phanerogamic plants.