Whether the androecial structure of Chloranthus represents a single stamen with four pairs of sporangia or three independent stamens that have undergone fusion with one another towards their base, has remained a major controversial issue. In literature, it has been described as "a single stamen", "three stamens", "three anthers", "a single tripartite anther", or "a three-lobed filament". Two classes of hypotheses were also proposed to interpret its evolutionary process, but no accordance has reached yet. In this study, we observed the floral organogenesis of C. sessilifolius K. F. Wu, a perennial herb with androecial lobes cohered only at the base. Inflorescence primordium, produced at the end of leafy shoots, is dome-like at the beginning and then elongates upwards, from which bract primordia initiate almost decussately. Floral primordium, arising from the axil of the bract, soon becomes a scale-like structure, with androecial primordium originating from its adaxial margin, and gynoecial primordium in its abaxial position. As three primordia of androecial lobes become visible in the adaxial margin of the floral primordium, four thecae are already in differentiation, and the gynoecial primordium appears as a shallow disc. The androecial lobes do not extend its length until the thecae approach maturity, and the elongation of the androecial lobes is simultaneous with the differentiation of the stigma. Ontogenetically, C. sessilifolius shares many character states with Sarcandra species, and more with C. spicatus (Thunb.) Makino. Based on these results and those of Endress, combined with evidence from neobotany, palaeobotany and molecular systematics, the morphological nature of the androecium of Chloranthus is further discussed. The second hypothesis of Endress, that the androecial structure of Chloranthus might have arisen by splitting of a single stamen with 2 marginal thecae, seems to be the most plausible interpretation.

Key words: androecium, Chloranthaceae, Chloranthus, floral organogenesis