Figure 1.

Developmental path to unisexuality in male and female flowers in monoecious and dioecious species. In Quercus suber, Populus tomentosa, Spinacea oleracea, and Thalictrum dioicum, sex differentiation occurs prior to flower organ primordia initiation (Varela and Valdiviesso, 1996; Boavida et al., 1999; Sheppard et al., 2000; Di Stilio et al., 2005; Pfent et al., 2005; Sather et al., 2010). In Carica papaya, the pistil degeneration is clear at early stages of organ development in male flowers but female flowers have no traces of stamens (Ronse Decraene and Smets, 1999). Stamen and pistil development in Cucumis sativus, Cucumis melo, and Zea mays arrests during early organogenesis (Le Roux and Kellogg, 1999; Bai et al., 2004; Boualem et al., 2008). The abortion of stamens in Silene latifolia and Diospyros lotus occurs later than the abortion of the pistil, at a pre-meiotic stage (Grant et al., 1994; Akagi et al., 2014). In Asparagus officinalis, the arrest of stamens occurs somewhat early than the arrest of pistils (Caporali et al., 1994). Stamen and pistil degeneration in Vitis vinifera occurs at the post-meiotic stage (Caporali et al., 2003).