Abstract:Semiaquilegia is an Asia endemic genus in the Ranunculaceae, but the data on floral morphogenesis of this genus, are still lacking. In this paper, we used scanning electron microscopy to study the floral development of S. adoxoides (DC.) Makino to indicate the flower diversity and phylogeny and further to provide morphologic development evidence of S. adoxoides and its related plants. Our results indicate that: (1) the sepals, petals and stamens of this genus are initiated spirally, whereas the carpels are initiated whorled. The staminodium number and positions are not sure. The phyllotaxis is whorled. (2) Primordia of the sepals are lunular and truncate, but those of other organs are hemispherical and rounded. (3) Petal development is delayed and there is an abaxial knob at the base. The carpel primordia are plicate, and mature ovule is anatropous and unitegmic. There is an appendage on the placenta. (4) Semiaquilegia shows similar floral development features as Aquilegia and Urophysa, which supports the relationship inferred by DNA sequence data. At the same time, other characters, e.g. small flowers, few stamens, sterile stamens, and carpels, absent orthostichies, longer inner integument, support Semiaquilegia as a distinct genus.