Palmaria mollis stat. nov.: a newly recognized species of Palmaria (Rhodophyceae) from the northeast Pacific Ocean

Attempts were made to hybridize Palmaria palmata (L.) O. Kuntze from the North Atlantic Ocean with Palmaria palmata f. mollis (Setchell and Gardner) Guiry from the eastern North Pacific Ocean. No hybrids were obtained in reciprocal crosses, although fertilization was readily achieved for control crosses within each taxon. The number and placement of carpogonia on well-developed female gametophytes (disc diameter, 100–150 μm) was different for the two taxa. The Atlantic plants had comparatively few carpogonia (1–10), which were always found at the center of the holdfast disc or on young upright fronds, whereas the Pacific plants had many carpogonia (15–60), which were most commonly located away from the centermost portion of the disc and were never observed on developing fronds. The two taxa also differed in their susceptibility to a small parasitic Oomycete of the genus Petersenia Sparrow, which is pathogenic for f. mollis but did not infect the Atlantic plants. Cytological examination revealed that f. mollis has n = 21 chromosomes, the same as P. palmata from the north Atlantic Ocean. In view of the genetic isolation between the two forms, P. palmata f. mollis is raised to specific status as Palmaria mollis (Setchell & Gardner) van der Meer & Bird.