Abstract
Sporolithon is a non-geniculate, marine taxon that occurs in tropical to subtropical and warm temperate habitats worldwide. On the basis of specimens collected from offshore Louisiana and Florida in the Gulf of Mexico, Sporolithon sinusmexicanum sp. nov. is described. rbcL and psbA sequence analyses showed that S. sinusmexicanum is closely related to Sporolithon yoneshigueae (type locality: Bahia, Brazil). These two species can be distinguished by the number of rosette cells (10–12 in S. sinusmexicanum vs. 19–24 in S. yoneshigueae) and by the habit of the tetrasporangial structures after spore release (sloughed off in S. sinusmexicanum vs. overgrown and buried in Sporolithon yoneshigueae).