چکیده
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Development of the capitulum inflorescence with different types of florets in Asteraceae is an interesting issue in
the field of plant evolution and development. In this study, ontogeny of the inflorescence and florets of Osteospermum
ecklonis (DC.) Norl., an ornamental and evergreen subshrub, was investigated using epi-illumination light microscopy. The
initiation and subsequent development of florets on the highly convex inflorescence apex occurred acropetally, except for
the ray florets, which showed a lag in initiation. Organogenesis in disc florets started with unidirectional initiation of corolla
lobes from the adaxial side and then proceeded by simultaneous appearance of five stamen and finally two median carpel
primordia. Significant developmental features included the lack of pappus differentiation, formation of nonsyngenesious stamens,
and formation of the ovule-less ovary. Ray florets showed significant differences from disc florets as reflected by the
zygomorphic shape of floral apex and shift of floral merosithy from pentamery to tetramery. Also, expansion of corolla
lobes to form the ligule and the formation of staminodia were observed. It is hypothesized that the actinomorphic pentamerous
disc florets are most primitive among the family from which the tetramerous ray florets are derived. Accordingly, ray
florets evolved from disc florets under long-term selective pressure and play a crucial role in enhancing reproductive success.
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