Abstract: Caytoniales are an important group of seed plants, and the nature of their female reproductive organ may influence interpretations of the seed plant phylogeny and the origin of angiosperms. Although not convincingly demonstrated by clear evidence, cupules on previously described specimens were interpreted as being distichously arranged, implying that the cupule bearing organ in Caytoniales was a pinnate megasporophyll. Here a female reproductive organ of Paracaytonia hongtaoi gen. et sp. nov. (Caytoniales) is reported from Liaoning, China. The well preserved specimen clearly demonstrates a spiral arrangement of cupules along the reproductive axis suggesting that the cupule-bearing organ in Caytoniales is not a megasporophyll but a branch. This new information on axial nature of the cupule-bearing organ in Caytoniales has significant implications on the placement of Caytoniales in the seed plant phylogeny and interpretation of the relationship between Caytoniales and angiosperms.

Key words: angiosperms, cupule, evolution, Paracaytonia, Caytoniales, seed plants, systematics, Yixian Formation.