Which are the pioneer species in hydrarch succession of plants?

Hydrarch succession takes place in wetter areas and the successional series progress from hydric to mesic conditions.

The pioneer species in primary succession in water are small phytoplanktons.

These phytoplanktons are replaced with time by free-floating angiosperms, then by rooted hydrophytes, sedges, grasses, and finally trees.

Crustose lichens are the pioneer species in xerarch succession on bare rocks.

Answer: Small phytoplanktons