In 1905 Kylin collected a species of Porphyra from the west coast of Sweden, which he described as P. elongata (Aresch.) Kylin. However, P. laciniata var. elongata Aresch., the intended basionym, was never validly published so that the name P. elongata must be attributed directly to Kylin. Sequence data of the rbcL plastid gene obtained from Kylin's original material of P. elongata differed by only a single nucleotide transition from the rbcL sequences for the holotype and isotype of P. rosengurttii Coll et Cox. In this paper, we lectotypify P. elongata and propose P. rosengurttii as a synonym.