Observations on navicula-ulvacea a rare foliose marine diatom

N. ulvacea (Berkeley ex Kuetz.) PT Cleve, a marine colonial blade-forming diatom originally discovered in Scotland, was collected at North Rustico, Prince Edward Island, Canada, during the winter of 1971. It formed dense stands of Porphyra-like fronds, ranging up to 60 mm long .times. 20 mm wide. These occurred under ice-covered water on rocks 1-2 m below zero tide. Comparisons made at the light and scanning electron microscope level compared favorably with original Aberdeen material. Clonal cultures established from single cells at first also formed blades, but rarely more than 10 mm long. In numerous serial subcultures made since 1971 no further blades were formed. Growth consisted of well-separated cells or short filaments scattered over the bottom and sides of the vessels. Older cultures developed prostrate sheets of filaments embedded in a mucilagenous matrix and occasional bubble-like eruptions. N. ulvacea probably occurs in a prostrate form in nature, perhaps more commonly than in the blade form. A discussion on nomenclature is included.