Heterodichogamy in Ascarina lucida (Chloranthaceae)

Premise of research. Among early-divergent angiosperms, Ascarina is an important genus whose sexual system, inflorescences, and flowers have been inconsistently interpreted. While both monoecy and dioecy have been reported in the genus, our observations show that Ascarina lucida is monoecious and wind pollinated and its dimorphic inflorescence morphology is linked with dimorphism in type of dichogamy. Methodology. We studied a wild population of the New Zealand tree A. lucida. We recorded anthesis of male and female flowers on 30 plants each week throughout its 20-wk flowering period (late June to early November). We also estimated flowering gender among plants. Pivotal results. Ascarina lucida populations are monomorphic for gender but dimorphic for both cymule structure and type of dichogamy. Furthermore, the morphs are linked, such that plants with one cymule type are protandrous and plants of the other cymule type are protogynous. Our samples were statistically consistent with an expected 1∶1 morph ratio. In a first flowering pulse (6–10 wk), one morph presented female flowers, while the other presented male flowers. In the second pulse (7–8 wk), the flower sexes presented by each morph were reversed. Protandrous plants had a gap of several weeks between flowering pulses, but the tails of the female and male phases overlapped by 3 wk in a few protogynous plants. Conclusions. We conclude that A. lucida is heterodichogamous. This is the first record of heterodichogamy in Chloranthaceae and in the New Zealand flora. Heterodichogamy explains previous reports of dioecy in A. lucida and might explain conflicting reports of sexual systems in other species. We discuss the potential for a pathway from heterodichogamy to dioecy in Ascarina.