Morphology and life history of Amphora commutata (Bacillariophyta) I: the vegetative cell and phylogenetic position

Abstract

Sato S., Tamotsu N., and Mann D.G. 2013. Morphology and life history of Amphora commutata (Bacillariophyta) I: the vegetative cell and phylogenetic position. Phycologia 52: 225–238. DOI: 10.2216/12–072.1Amphoroid diatoms are recognized in the light microscope by their strongly dorsiventral frustules; their raphe system lies close to the ventral margin of the valve, and their girdle is much wider on the dorsal side. Historically, these diatoms were classified into the genus Amphora, although heterogeneity has long been pointed out based mainly on frustule fine structure, chloroplast arrangement, and molecular phylogeny. In this study detailed observations were undertaken on the frustule of an amphoroid species Amphora commutata. Distinct features of this species were the hyaline ventral side of the valve and hitherto unknown apical pores. The ontogeny of the valve and girdle bands was also reported. A molecular phylogenetic analysis of Amphora species, including representatives of the subgenera Amphora, Oxyamphora and Diplamphora, was performed, based on nuclear encoded small subunit (SSU) rDNA. The best tree showed paraphyly of amphoroid diatoms and also suggested that the subgenus Diplamphora, which includes Amphora commutata and was characterized by the structured, porous girdle bands, may be paraphyletic with respect to the monophyletic subgenus Amphora, which has mostly plain girdle bands; however, hypothesis testing with constrained topologies did not reject the monophyly of either group.