Sporolithon molle (Heydrich) Heydrich (Sporolithales, Corallinophycidae, Rhodophyta): an addition to the Atlantic flora found on a remote oceanic island

Sporolithon molle (Heydrich) Heydrich has previously only been reported from the Red Sea, Arabian Gulf, Indonesia, and eastern Australia. The species is reported for the first time from the Atlantic Ocean where it was found in the remote oceanic island of Trindade, Brazil. This study provides a comparative account of tetrasporic plants from the Atlantic Ocean against those from the other known locations and from other well-described species of the genus Sporolithon. The specimens reported here, presented all the features of the genus, namely: flared epithallial cells, cells of adjacent filaments joined by both cell fusions and secondary pit connections, cruciately divided tetrasporangia formed within sori; and tetrasporangia bearing apical pore plugs and formed on a single stalk cell. Sporolithon molle differs from other species of Sporolithon mainly by the absence of a layer of elongate cells at the base of tetrasporangial sori. Samples from Trindade differ slightly from the type collection and from specimens from other known locations by the tetrasporangial sori which can be flush to slightly raised (to 3 cells) above the surrounding vegetative thallus surface as opposed to being flush only in all material reported previously.