New apomictic pathway in Myrtaceae inferred from Psidium cattleyanum female gametophyte ontogeny.
Adventitious embryony and aposporous apomixis have been described in Myrtaceae. Psidium cattleyanum Sabine is a South American species with commercial potential as a fruit tree in natural areas. Interestingly the species is listed among the 100 world's worst invasive alien species. Morphological and molecular uniformity of the offspring obtained from seeds suggests an apomictic pathway of reproduction. The aim of this study was to describe the ovule ontogeny and embryology of selected materials of Psidium cattleyanum for two infraspecific entities Psidium cattleyanum f. cattleyanum and Psidium cattleyanum f. lucidum O. Deg. and to identify possible ontogenetic evidence of apomictic embryo sac development. We collected and analyzed anatomical sections of flowers from very early stages of development until fruit formation started. Both taxa showed the typical ontogenetic pattern of Myrtaceae. Ovules are anatropous, bitegmic and crassinucelate and they show a zig-zag micropyle. As the megaspore mother cell enlarges in the nucellus no evidence of meiosis was registered. A megaspore-like cell was observed in the following stages of development. The embryo sac is Polygonum type with persistent antipodals. Immature seeds have nuclear endosperm. Development patterns of embryo sac and non-meiotic origin of the megaspore lead us to reject the adventitious embryony and apospory cited for other taxa in the family and, instead, a possible disploporic origin of the embryo sac is proposed for the first time for Myrtaceae.