A new West African species of Trichosolen (Chlorophyceae)

Trichosolen retrorsa sp. nov. was collected on calcareous cobbles at a depth of 15 m below Chart Datum off the coast of Ghana (tropical West Africa). This species is distinct from all others in the genus in that the gametangia arise laterally near the base of the ramelli, are directed back towards the central axis, and develop one or two distinct terminal papillae. Trichosolen has priority over Pseudobryopsis with which it is congeneric. The following new combinations are therefore necessary: T. blomquistii, T. gracilis, T. longipedicellata, T. planktonica and T. solomonensis.