Seed shape quantification in diverse species of the families belonging to the order Cucurbitales is done based on the comparison of seed images with geometric figures. Quantification of seed shape is a useful tool in plant description for phenotypic characterization and taxonomic analysis. J index gives the percent of similarity of the image of a seed with a geometric figure and it is useful in taxonomy for the study of relationships between plant groups. Geometric figures used as models in the Cucurbitales are the ovoid, two ellipses with different x/y ratios and the outline of the Fibonacci spiral. The images of seeds have been compared with these figures and values of J index obtained. The results obtained for 29 species in the family Cucurbitaceae support a relationship between seed... shape and species ecology. Simple seed shape, with images resembling simple geometric figures like the ovoid, ellipse or the Fibonacci spiral, may be a feature in the basal clades of taxonomic groups.