Abstract: The objectives of this study were to characterize the floral organ development of the flowers with single- and triple-whorled petals in lisianthus ( Eustoma grandiflorum ). The first and second buds in a primary inflorescence were collected. A floral shoot apex of each bud was dissected, observed and recorded under stereoscope. The results were as follows: 1. Floral organ development in both types of flowers was divided into five stages from the beginning of flower bud differentiation, i1e. , (1) appearance of flower buds and the initiation of the development of ( 2) sepal primordia, (3) petal primordia, (4) stamen primordia, and (5) pistil primordium. 2. It took about 12 days for flowers with single-whorled and about 15 days for those with trip le-whorled to develop from the initiation to the end. 3. In both types of flowers, the number of sepals, petals and stamenswas five, except only one pistil. The number of petals was five and fifteen for the flowerswith single-whorled and trip le-whorled petals, respectively.

Key words: Eustoma grandiflorum, Floral organ, Flower bud differentiation, Trip le-whorled petal