The taxonomie position of Cyclotella andina Theriot, Carney et Richerson, a tropical freshwater planktonic diatom originally identified from Lake Titicaca, is modified based on morphological characters. The presence of striae arranged in discrete fascicles on the valve- face, coupled with the placing of fiilto- and rimoportulae on the same internal costa below the position of external spines (or on the valve face/mantle region in spineless individuals), form the basis to transfer this species from the genus Cyclotella Kützing to the genus Cyclostephanos Round. Morphometric analyses of 350 valves from seven populations from three Andean lakes demonstrate a morphological continuum in fossil and modern assemblages. Principal Component Analysis (PCA) shows that three main factors characterize most of the variability in morphology. PCI (λ1 = 71.7%) is a size-related component (e.g. valve diameter); PC2 (λ2 = 23.9%) is a size-free component that relates the length of biseriate to uniseriate areolae, and PC3 (λ3 = 1.73%) represents the ratio between the number and distance of biseriate or uniseriate areolae. We herein propose the taxonomie transfer of Cyclotella andina as Cyclostephanos andinus comb. nov. © 2004 Taylor & Francis Group, LLC.