Taxonomy, morphology and distribution of the Sellaphora stroemii complex (Bacillariophyceae)

Live and treated materials from three populations of diatoms collected in Italy, Slovakia and Spain, identified in previous inventories as Navicula stroemii Hust. sensu Krammer et Lange –Bertalot, were examined under light and scanning electron microscopy. The analyses highlighted the typical single H–shaped plastid, characteristic of the genus Sellaphora. Considering this, we thoroughly investigated type materials from the Sellaphora stroemii complex. According to the standard European diatom flora of Krammer & Lange –Bertalot (1986: Süßwasserflora von Mitteleuropa 2/1), six species should be considered as taxonomic synonyms of Navicula stroemii, now Sellaphora stroemii (Hust.) H. Kobayasi in Mayama et al.: Navicula aggerica E. Reichardt, N. rivularis Hust., N. subbacillum Hust., N. subcontenta Willi Krieg ., N. vasta Hust. and N. ventraloides Hust. The type materials of these species were examined using both light and scanning electron microscopy and geometric morphometric analysis. The analysis of the valve ultrastructure demonstrated the affiliation of Navicula aggerica, N. subbacillum, N. vasta and N. ventraloides to the genus Sellaphora. A Principal Component Analysis based on the shape of the valve outline, allowed us to define the European taxa Sellaphora stroemii, S. ventraloides and S. aggerica as three separated taxa, clearly distinct from the Indonesian diatom Sellaphora subbacillum, comb. nov. Moreover, considering the need of a replacement name for Navicula subcontenta (Krieger 1943), already validly published by Hustedt in 1942, we propose the new name Navicula petrmarvanii nom. nov. for Krieger’s species.