Ovule and megagametophyte development in selected species of Apeibeae and Grewieae (Malvaceae–Grewioideae) from South America and its systematic implications

Abstract

This is the first embryological report of the Grewioideae subfamily, which is meant to contribute to the characterisation of the genera Corchorus, Luehea and Triumfetta. Ovule and female gametophyte development in C. argutus, L. divaricata and T. semitriloba was analysed. The ovules of all species are anatropous, bitegmic and of crassinucellate mixed type. The micropyle of the studied species is formed by the outer integument (exostome). The ovule of L. divaricata differs from those of the other two species because the chalazal tissue expands forming a cap, which gives rise to a wing in the seed. All species present one hypostase. The megaspore mother cell gives rise to a linear megaspore triad in C. argutus and L. divaricata, whereas in T. semitriloba, triads and diads can be observed in the same ovule. The chalazal megaspore develops a seven-celled and eight-nucleate female gametophyte corresponding to the Polygonum type. The synergids of L. divaricata have hooks and a conspicuous filiform apparatus. The antipodal cells in C. argutus are persistent, whereas in the other species, they are small and ephemeral. The embryological characters are compared with those of other taxa within the family and the megagametophyte formation in these species is discussed.