Heterodichogamy of a Novel Type in <i>Hernandia</i> (Hernandiaceae) and Its Structural Basis

Heterodichogamy is reported for the first time in the family Hernandiaceae (Laurales); furthermore, this heterodichogamy is of a novel type hitherto not reported in angiosperms. In Hernandia nymphaeifolia, which has unisexual flowers and is monoecious, two kinds of individuals were found: one kind with exclusively female flowers open in the morning and male flowers open in the afternoon and the other kind with the reverse behavior. The flowers are arranged in compound thyrses with cymes of two male and one female flower. Developmental studies confirm an earlier interpretation of these triads as monochasia with the sequence male‐male‐female. Surprisingly, though, the sequence is reversed at anthesis: most triads flower with the sequence male‐female‐male. Flower development shows that the gynoecium is unicarpellate (and not pseudomonomerous). In male flowers there are three rudimentary mounds (as yet overlooked) alternating with the stamens, which may correspond to those mounds in the female flowers that are united into a ring‐shaped nectary and may represent extremely reduced staminodes. As heterodichogamy is an apparently rare phenomenon in angiosperms, it is of interest that heterodichogamy, although of a different type, has long been known in some Lauraceae, the sister family of Hernandiaceae. For an evolutionary understanding, the flowering behavior of the other genera of Hernandiaceae should be studied.