Significance of floral axis and staminal features in tracing phylogeny of Cleome species

Abstract

Taxonomic delimitation, phylogeny of Cleome L. species and relative closeness between three allied families, Capparaceae, Cleomaceae and Brassicaceae, are enigmatic and yet to be resolved comprehensively. The genus Cleome of Cleomaceae represents a cosmopolitan assemblage of species with wide variability in morphological features sharing morphological similarity with both Capparaceae and Brassicaceae. In the present study, floral-axis and staminal features, along with habit and leaf characters, were employed in tracing the phylogeny of Cleome species not explored earlier. The parameters proved unique in solving the phylogenetic puzzle of Cleome, allowing to speculate on the origin of woody and non-woody herbaceous species of Cleome from two separate species aggregates of Capparaceae (palmate-leaved Crateva aggregate and simple-leaved Capparis aggregate, respectively), also to establish phylogenetic linkage between three families, Capparaceae, Cleomaceae and Brassicaceae. Evolutionary changes were directed towards the gradual shortening and suppression of elongated floral axis to discoid thalamus, gradual reduction in the number and size of stamens, and flower size with habitual transformations from shrubby to herbaceous form. Cleome appeared as a connecting link between Capparaceae and Brassicaceae, and the interpretations derived showed significant concomitance with APG IV classification system.