Evolution of the monocot gynoecium: evidence from comparative morphology and development in Tofieldia, Japonolirion, Petrosavia and Narthecium

We present new comparative morphological and developmental data on gynoecia of three genera of early-divergent monocots: Tofieldia (Tofieldiaceae, Alismatales), Petrosavia and Japonolirion (Petrosaviaceae, Petrosaviales) and one lilioid monocot: Narthecium (Nartheciaceae, Dioscoreales). Our data show significant differences between the genera examined, and are congruent with the splitting of former Nartheciaceae sensu Tamura (1998) into families Tofieldiaceae, Petrosaviaceae NB-cosistent with later and Nartheciacae (APG II 2003). Our investigation confirms the presence of at least partial carpel fusion in all taxa examined. Previous data indicating apocarpy in Japonolirion, some Petrosavia and Tofieldia could be due to late postgenital carpel fusion in these plants. Syncarpy also characterises other early-divergent monocot lineages such as Acoraceae and Araceae. It is most parsimonious to regard syncarpy as a primitive condition for monocots, but an alternative scenario suggests that apocarpy is plesiomorphic among monocots, involving multiple origins of syncarpy. The latter hypothesis is supported by significant differences between gynoecia of early-divergent monocots, including different modes of carpel fusion.