Pseudo-nitzschia obtusa (Hasle) Hasle & Lundholm
Differences between P. seriata f. obtusa and P. seriata f. seriata ITS sequences justified raising P. seriata f. obtusa to the rank of species (Lundholm et al. 2005).
Growth rates of P. obtusa were similar to P. seriata (0.55 0.65 per day respectively) under the same conditions (Lundholm et al. 2005). The upper pH limit for growth in P. obtusa was 9.1.
P. obtusa is similar to P. turgidula, P. brasiliana and P. americana in having truncate ends in girdle view and rounded ends in valve view (Lundholm et al. 2005).
Pseudo-nitzschia obtusa can be found primarily in Arctic coastal regions. From Hasle 2002: Atlantic: Kings Bay, Svalbard, 79°N (Hasle and Heimdal, 1998) to Gulf of St. Lawrence, ca 51°N ( Bérard-Therriault et al., 1999) including Barents Sea and east and west coast of Svalbard ( Quillfeldt von, 1996), Bear Island ( Metzeltin and Witkowski, 1996. Metzeltin, D., Witkowski, A., 1996. Diatomeen der Bären-Insel. In: Lange-Bertalot, H. (Ed.), Iconographia Diatomologica, Annotated Diatom Micrographs, Taxonomy, Vol. 4. Koeltz Scientific Books, Königstein, Germany, pp. 3–232.Metzeltin and Witkowski, 1996), Norwegian coastal waters from ca 63°N and northwards ( Hasle et al., 1996), Helsingør, Denmark ( Hasle, 1965), Irish coastal waters ( Cusack et al., 2000); Resolute Bay, Canadian Arctic and northeast of Greenland ( Quillfeldt von, 1996), Hudson Strait ( Hasle, 1965). Pacific: off Kamchatcha, ca 60–55°N and Kuril Island, ca 45°N (unpublished observations).