Abstract:Floral development of Blyxa japonica (Miq)Maxim, ex Asch. et Gürk(Hydorcharitaceae) has been observed under scanning electron microscope (SEM). The sepal primordia first initiate on radii verticillately. A whorl of alternisepalous petal primordia forms nearly simultaneously. Three antisepalous stamen primordia initiate verticillately, alternating with petal primordia. At the base of petal primordia, three antipetalous gynoecial primordia appear verticillately. Compared with other genera in the family, the flower of Blyxa japonica shows many primitive characteristics，such as bisexual，actinomorphic an d numerous ovules，whereas the number of floral organs is fixed as 3 shows its interm ediate evolutionary leve1． Floral organongensis initiating verticillately and inferior ovary indicate advanced characteristics of Hydrocharitaceae in Alismatidae.