Floral ontogeny, pattern formation, and evolution in Hibbertia and Adrastaea (Dilleniaceae)

Floral development was compared with scanning electron microscopy in 12 Aus tralian species of Hibbertia representing most of its morphological variati on, and in the related Ardastaea (Dilleniaceae). Calyx and corolla arise in quincuncial helices in radially symmetrical species, while the petals init iate unidirectionally from one side in zygomorphic species. Stamen number ( 3-200+) proliferates by centrifugal addition of individual primordia or by innovations of common primordia and ring meristems. Common primordia arise in single-stamen positions alternately with petals, and each produces one t o several stamens centrifugally that remain attached to a shared base and f orm a stamen fascicle. A ring meristem in Adrastaea initiates a whorl of fi ve stamens, alternate with the first stamens but outside their whorl. In ra dially symmetrical species of Hibbertia, a first ring of stamens is supplem ented centrifugally by additional stamens on a meristem ring. The first sta mens in zygomorphic species of Hibbertia initiate as a terminal ridge on th e floral apex, with subsequent stamens added centrifugally on one side and two carpels initiated on the opposite side. The carpels arise as a simultan eous ring in radially symmetrical flowers, or as a simultaneous pair in zyg omorphic species. Staminodial presence is viewed as of minor significance. Four pollinator syndromes are proposed for Hibbertia, related to differing floral architecture.