ORIGINAL ARTICLE Inflorescence and floral development in Ranunculus and three allied genera in Ranunculeae (Ranunculoideae, Ranunculaceae) Liang Zhao • Julien B. Bachelier • Hong-li Chang • Xian-hua Tian • Yi Ren Received: 15 February 2011 / Accepted: 17 February 2012 / Published online: 30 March 2012 Ó Springer-Verlag 2012 Abstract The development of inflorescences and flowers of three species of Ranunculus and three allied genera (Ceratocephala, Halerpestes, and Oxygraphis) (Ranuncu- leae, Ranunculaceae) was studied comparatively using scanning electron microscopy (SEM). Our results showed that both the inflorescence branching patterns and the floral morphogenesis in Ranunculeae are extremely labile. Inflorescences range from a thyrsoid to a solitary flower, with intermediate branching patterns in which sometimes only the terminal flower of the inflorescence main axis fully develops, such as in Ceratocephala and Halerpestes. Only in Oxygraphis is the flower truly solitary. In all species, sepal primordia are broad, crescent-shaped, and truncate, and the primordia of petals, stamens, and carpels are rather small and hemispherical, and very similar to each other. The plastochron between the last sepal and the first petal is relatively long. At the onset of androecium or gynoecium development, the regular spiral pattern of the perianth may become irregular in Ceratocephala and Oxygraphis, whereas spiral and whorled patterns may co- occur in Ranunculus and Halerpestes. The development of the petals is delayed with regard to that of the other floral organs in all species studied here, except for Oxygraphis. Our study confirms that, for solitary flowers, increased number of petals and the shape of the ventral nectary may have evolved independently many times, as suggested by earlier molecular phylogenetic studies and ancestral char- acter reconstructions. With respect to the remainder of the tribe, Oxygraphis displays several autapomorphies, such as nondelayed development and increased number of petals, which will be of interest for comparative molecular developmental studies. Keywords Batrachium Á Ceratocephala Á Floral morphology Á Floral phyllotaxis Á Halerpestes Á Oxygraphis Á Inflorescence (branching pattern) Introduction Ranunculus is composed of about 600 species of annual and perennial herbs distributed nearly all over the world, although the species are scant in the tropics and subtropics (Tamura 1967). The circumscription of such a large and widespread genus is very difficult, and systematic treat- ments are often restricted to a geographic area (for URSS, Ovczinnikov 1937; for North America, Whittemore 1997; for Europe, Tutin and Cook 1993; for details on these classifications, see Ho ¨randl et al. 2005). Also, the sys- tematics and affinities of Ranunculus within Ranuncula- ceae vary greatly depending on the authors, and numerous classifications have been proposed, based mostly on L. Zhao Á X. Tian Á Y. Ren (&) College of Life Sciences, Shaanxi Normal University, Xi’an 710062, China e-mail: renyi@snnu.edu.cn L. Zhao College of Life Sciences, Northwest A and F University, Yangling 712100, China J. B. Bachelier Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA J. B. Bachelier Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA H. Chang School of Life Sciences, Northwest University, Xi’an 710069, China 123 Plant Syst Evol (2012) 298:1057–1071 DOI 10.1007/s00606-012-0616-6