ORIGINAL ARTICLE Maytenus obtusifolia Mart. (Celastraceae): a tropical woody species in a transitional evolutionary stage of the gynodioecy– dioecy pathway Cristine R. Benevides • Isabella V. N. Haddad • Nata ´lia P. Barreira • Ana Tereza de A. Rodarte • Leonardo Galetto • Lygia Dolores R. de Santiago-Fernandes • Heloisa A. de Lima Received: 19 November 2012 / Accepted: 16 April 2013 Ó Springer-Verlag Wien 2013 Abstract ‘Gynodioecy–dioecy’ is one of the pathways by which dioecy can arise from hermaphroditism. Studies on sex determination and development of gynodioecious sys- tems have focused on temperate and/or annual species. Little is known about the evolutionary dynamics of gyno- dioecy and dioecy in perennial tropical species, where these systems have more frequently evolved. Maytenus obtusi- folia is an abundant species in restingas in southeastern Brazil. The sexual system of M. obtusifolia was investi- gated by studying the floral structure and reproductive biology. We considered the sexual system as an interme- diate step in the pathway gynodioecy-dioecy. The charac- terization of the hermaphrodite morph was complex, because of a gradient of variation in floral morphology and reproductive characteristics (sizes of the style and stigmatic surface, pollen viability, embryo sacs containing hyper- trophied synergids, and fruit set). This variation leads to different proportions of functional male and female flowers among hermaphrodite plants and is responsible for the different levels of reproductive success. Female reproduc- tive success and pollen viability were negatively correlated with the hermaphrodite morph (r =-0.67). The higher fruiting intensity and fruit/flower ratio of females (41 %) compared to hermaphrodites (2 %) and the fact that female plants produce more and better-quality seeds support the female compensation. We suggest that female sterility may be linked to the set of changes in the carpels. The differ- ences in the quality and quantity of pollen grains of her- maphrodite plants, and the similar individual rates of pollen viability observed for three consecutive flowering events, may indicate a relationship with nuclear cytoplasmic sex determination. Keywords Sexual system Á Floral anatomy Á Female compensation Á Restinga Introduction Flowering plants exhibit a great diversity of sexual systems. Most of them are hermaphroditic and strong evidence indi- cates that the production of bisexual flowers is the ancestral condition in angiosperms. Dioecious systems (separate male and female individuals in a population) occur in approxi- mately 6–7 % of species; however, it is represented in close to half of all angiosperm families and has evolved repeatedly from hermaphroditism on at least 100 occasions (Renner and Ricklefs 1995; Charlesworth 2002). ‘Gynodioecy–dioecy’ is one of the recognized pathways by which dioecy can arise from hermaphroditism (Bawa 1980; Webb 1999; Torrices et al. 2011). The first step in this pathway involves the appearance and establishment of a male sterile mutant (i.e., female) in a cosexual population (Lloyd 1974, 1975; Barrett 2002). Since the mutants do not produce pollen grains, they have a reproductive disadvan- tage when compared with hermaphrodite individuals. So, an increase in production and quality of its fruits and seeds, formed only through cross-fertilization, compensates the loss of male function. This compensation allows the C. R. Benevides (&) Á I. V. N. Haddad Á N. P. Barreira Á A. T. de A. Rodarte Á L. D. R. de Santiago-Fernandes Á H. A. de Lima Departamento de Bota ˆnica, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 20940-040, Brazil e-mail: cristinebenevides@gmail.com L. Galetto Departamento de Diversidad Biolo ´gica y Ecologı ´a and Instituto Multidisciplinario de Biologı ´a Vegetal (CONICET), Universidad Nacional de Co ´rdoba, CC 495 5000 Co ´rdoba, Argentina 123 Plant Syst Evol DOI 10.1007/s00606-013-0826-6