The formation of capitulum inflorescence with two different types of floret is an interesting issue in floral biology and evolution. Here we studied the inflorescence, floral ontogeny and development of the everlasting herb, Xeranthemum squarrosum, using epi-illumination microscopy. The small vegetative apex enlarged and produced involucral bracts with helical phyllotaxy, which subtended floret primordia in the innermost whorl. Initiation of floret primordia was followed by an acropetal sequence, except for pistillate peripheral florets. The origin of receptacular bracts was unusual, as they derived from the floral primordia rather than the receptacular surface. The order of whorl initiation in both disc and pistillate flowers included corolla, androecium and finally calyx, together with the gynoecium. The inception of sepals and stamens occurred in unidirectional order starting from the abaxial side, whereas petals incepted unidirectionally from the adaxial or abaxial side. Substantial differences were observed in flower structure and the development between pistillate and perfect florets. Pistillate florets presented a zygomorphic floral primordium, tetramerous corolla and androecium and two sepal lobes. In these florets, two sepal lobes and four stamen primordia stopped growing, and the ovary developed neither an ovule nor a typical stigma. The results suggest that peripheral pistillate florets in X. squarrosum, which has a bilabiate corolla, could be considered as an intermediate state between ancestral bilabiate florets and the derived ray florets.

The inflorescence and floral ontogeny of the oleaceous tropical bush, Jasminum fruticans L. were studied using epi-illumination light microscopy and compared with other Oleaceae. The flowers are arranged in a thyrsoid inflorescence with a determinate pattern of development. Deviations from the common pathway of floral ontogeny in Oleaceae observed in J. fruticans are characterised by pentamery in calyx and corolla, diagonal position of sepals, some deviation from acropetal and simultaneous initiation of floral organs. Sepals are helically initiated, beginning with the abaxial sepal. Formation of petal lobes from the ring meristem also is not simultaneous with the initiation of three petals before the others. Concurrently with the formation of corolla ring, two stamens are initiated sequentially. Two median carpels are the last organs to be initiated. Unusual features of organ enlargement include the quincuncial-imbricate aestivation of the corolla and formation of trichomes on the distal portion of petals and stamens.