Morphometric Analysis of Shape of Specimens From the Neotype of Tabellaria Flocculosa (Bacillariophyceae)

Shape variation of 67 specimens from the neotype slide of Tabellaría flocculosa was analyzed by computer‐assisted morphometric techniques. Coefficients of a Legendre polynomial expansion of specimen shapes are shape descriptors used in principal component analysis (PCA). The first PC axis (PC1) is highly correlated with valve length. Variation along PC, is a combination of increase in width with a reduction in the distance between central and terminal inflations. The second axis (PC2) is the major length‐free component of shape variation. Variation in PC2 scores is related to the degree of constriction between the poles and the center. Shape variability increases as specimen length decreases. Three nonexclusive hypotheses can explain this: 1) different genetic entities are involved, 2) control of shape is strict in specimens longer than 35 μm, but not for those less than 35 μm, 3) the pattern of variation reflects environmental variation during the period of development of the population.