Taxonomic significance of inflorescences, floral morphology and anatomy in Passerina (Thymelaeaceae)

Abstract

Comparative studies were undertaken on the inflorescence, bracts and floral morphology of all taxa of the genus Passerina L. in southern Africa. Information is given in tabular form and a key based on bract morphology is presented. Floral morphology supported the status of the infrageneric taxa and also proved to be of taxonomic significance in the genus. Controversy surrounding the interpretation of a number of floral morphological structures in Passerina has been resolved. Morphological and anatomical evidence allowed a re-interpretation of the structure of the receptacle, hypanthium and sepals, ovary type and position, structure of the seed coat, ovule type and position, obturator, fruit and seed. On this basis an authentic generic description of the floral morphology was compiled. Passerina is distinguished by the following set of characters, a very short floral receptacle, tubular hypanthium, petaloid calyx, absence of petals and petaloid scales, diplostemonous dimorphic androecium, extrorse anthers, superior ovary, anatropous, ventrally epitropous ovule, an obturator of elongated cells, a 1-seeded berry or an achene and tegmic seed with nuclear endosperm becoming cellular throughout. On this basis the flower in Passerina is considered a phylogenetically advanced structure, supporting the view that the genus is advanced within the Thymelaeoideae. The proposed taxonomic relationship between Thymelaeaceae and Malvales is confirmed by floral morphological evidence.