Abstract
1) The protuberances between the horns of Trapa correspond to intersepalial appendages of Lythrum.
2) The character of Hemitrapa is similar to that of Trapa in having four long modified sepals with recurved barbs four intersepalial appendages and a heterocotyledonous embryo, judging from the fruit shape.
3) Trapa and Hemitrapa belong to the same family of Hydrocaryaceae and are related to ancestral Lythrum by four sepals and four intersepalial appendages on the margin of the receptacle.
4) Trapa and Lythrum have in the mesophyll compound crystals of similar shape which differ from rhaphide crystals of Oenotheraceae.
5) Trapa kiharae Miki n. sp. whose fruits do not separate from the top of the peduncle is the only living species of Stipitrapa.
6) Remains of Lythrum tetrasepalum Miki n. sp. have closer relation than the living species to Trapa by possession of four sepals and distinct striations on the receptacle.
