Phyllotactic spectra in cacti: Mammilaria species and some genera from Rebutia group

Abstract

Phyllotaxis of globular or hemispheric cacti from Mammillaria genus and from Rebutia group shows the significant differences between the two groups. An extremely wide spectrum of phyllotaxis with many infrequent patterns has been found in Rebutia group while in Mammilluria genus it appears to be quite narrow with the main Fibonacci pattern dominant. Therefore one of possible factors responsible for these differences might be a genetic one. Ontogenetic transformations of phyllotaxis both continuous (quantitative) and discontinuous (qualitative) have been found in studied cacti. These developmental events together with dichotomy frequently occurring in some taxa increase the level of phyllotaxis diversity. As more than one expression of the pattern occurred due to continuous transformations in many studied cacti - the numbers of opposite spirals can no longer be treated as a feature of the diagnostic value in cactus taxonomy. Because of intense developmental changes significant is rather a range of phyllotaxis diversity (phyllotactic spectrum) than a single pattern or its expression in a given taxon.