Background:

Microorganisms have traditionally been considered cosmopolitan. Nevertheless, recent studies of diverse groups demonstrated that this is an erroneous concept. Reviews of diatoms from the Neotropics have shown high biodiversity and numerous endemic species. Colombia has great habitat diversity in relatively small areas due to its latitudinal position and topography, so it is an ideal site for biogeographic studies. One of the better represented genera in lowland rivers, Eunotia and Eunotia parasiolii, a Neotropical species, was reported in several countries in the region.

Goals:

In order to establish whether the three morphotypes found are discrete taxonomic entities, their morphometric data, fine morphology and geographical distribution were analyzed.

Methods:

170 periphyton samples corresponding to 83 lotic systems were analyzed. Samples were prepared following the CENT/TC 230 (2002) protocol. They were observed with light (LM) and scanning electronic microscope (SEM). Distribution maps were made using GIS and a Moran’s I autocorrelation spatial index was applied.

Results:

The analyses of several specimens collected at 83 lotic systems allowed us to differentiate a priori 3 morphotypes based on the valve outline, development of subapical costae, and striae density. The species was extensively distributed in the study area, in basins with different hydrogeomorphology and chemical characteristics. The morphological characteristics that distinguish these morphotypes varied gradually; besides, the morphotypes were randomly distributed.

Conclusions:

We conclude that Eunotia parasiolii is a species with a great morphological variability and wide distribution. We propose to emend the description of the species, since the original diagnosis does not include characteristics of the fine structure of the frustules and therefore is insufficient to differentiate it from its allied taxa.