On the type specimens of Fragilaria siamensis Østrup, its transfer to Fragilariforma and comments on the biogeography of the genus

Biogeography is a valid scientific endeavour for exploring diatom distributions because the concept of endemism is generally accepted and not considered an irrelevant idea – endemism is taken seriously because it has been documented for many species in many areas around the globe. But to study biogeography meaningfully one does not just need the recognition of endemism. What is required is a problem, such as explaining the diversity of species or species groups in the Southern hemisphere. This requires the identification of species or species groups that are demonstrated to be endemic in at least some of the areas of interest and are related in a very specific way (monophyly). This paper deals with the genus Fragilariforma, which has ca. 30 + included species (taxa) that can be divided into a Northern component and a Southern component, the latter potentially speaking to the origin of the southern hemisphere biota.