A classical example of petal-to-stamen transition is the flower of white water lily (Nymphaea alba s.l., Nymphaeaceae). The description in terms of classical plant morphology cannot reveal all morphological variation of transitional organs. Our aim was to describe transitional structures of Nymphaea flower using an integrated approach, which could adequately reflect the nature of transitional structures. We collected 25 water lily flowers from four regions of European Russia. All the organs of the flowers were measured (2479 organs in total). Our data were analysed graphically and by various methods of multivariate statistics. To reduce the influence of size we computed two integrated "hybrid" morphological indices. The Euclidean distances from "typical stamen" and membership coefficients of fuzzy clustering were also calculated. In addition, we tested the descriptive ability of landmark-based geometric morphometrics. Besides traditional petal-to-stamen transition in Nymphaea flowers, we documented intermediate organs between sepals and petals, which were close to sepals by their morphology. Traditionally gradual petal-to-stamen shifts were postulated for Nymphaea flower. In spite of this postulate, our application of computing Euclidean distances method, of "hybrid" indices and of cluster membership of fuzzy clustering revealed that petals, stamens and transitional structures could be efficiently separated by their characters. The analysis of these characters shows diversity in morphology of flowers, collected from distinct regions of European Russia, which could be of taxonomic importance. It is remarkable that different morphological feature shifts, leading to substitution of sepals by petals and of petals by stamens, occur asynchronously. Flowers were investigated as "populations", where any separate organ represents a single "individual". Thus methods, used in plant population biology, may be applied to flower organs. Morphological nature of these organs is better revealed via integral characteristics such as "hybrid" indices, distances and cluster membership.
The Belgian Journal of Botany (now known as Plant Ecology and Evolution) is an international journal open to all fields of plant sciences. Please note, however, that papers restricted to purely nomenclatural matters or to floristical data of only local interest will not be accepted. The Journal appears in one volume of two issues per year. It publishes reviews, original research papers, short notes, letters to the editor, and book reviews. Click here for current issues of this journal