Abstract: The floral organogenesis of Caldesia parnassifolia (Bassi ex L. ) ParI. was observed under scanning electron microscope (SEM). The primordia of the floral appendage initiated in trimerous pattern and acropetal succession. Three sepal primordia first initiated on radii spirally, and a whorl of three alternisepalous petal primordia formed nearly simultane ously after the inception of sepal primordia. The petal and stamen primordia initiated separately, and no petal-stamen complex was observed. The three anti-sepalous outer stamens arised after the initiation of petals, the other three inner (anti-petalous) stamens arised subsequently, and the six stamens were arranged in one whorl at subsequent stages of development, but still anti-sepalous and anti-petalous separately. The first whorl of 3 pistil(carpel primordia originated opposite the sepal primordia, while subsequent pistil primordia formed rapidly in alternation with the preceeding ones, each whorl with 1～3 pistils. The significance of the spiral, acropetal development of corolla is discussed.

Key words: Caldesia parnassifolia, Floral organogenesis