General shape and ultrastructure as taxonomic characters in diatoms: the case of the genus Bacteriastrum

Abstract

Ultrastructural studies conducted in the last three decades have redefined the circumscription of genera and species in diatoms. However, in the genus Bacteriastrum there is evidence that the general shape of the frustule is more informative than ultrastructural details, which are not significantly different from homologous characters of some Chaetoceros species. This clearly shows that also for some diatoms, as well as for many unicellular organisms, distinctive taxonomic characters have been chosen mainly opportunistically. Different approaches are discussed aimed at verifying whether these characters are appropriate to build a phylogenetic systematics.

Key Words:

• Bacteriastrum
• diatoms
• taxonomic characters