Abstract: Cypripedium flavum P.F.Hunt et Summerh. is an alpine perennial herb growing in Northwest Yunnan, China. The study on differentiation of its flower bud has been carried out. The results show that the process from bud formation to completion of floral organs differentiation lasts two years, and dormant buds can be subdivided into one-year buds, two-year buds and perennial dormant buds by their different developmental phases. From early June to July of the first year, two one-year buds emerge from the lateral base of the two-year bud and differentiate 7 to 9 spires before October and lay dormant in winter. In the next year, they (called 'two-year buds'now) start to grow in late April,and differentiate floral organs in summer. During this period,two new one-year buds develop. After this, usually only one of the two year buds continue growing. The other one lay dormant and usually do not develop again. It is called 'perennial dormant bud'. At the end of second growth season, an entire mix bud which contains spires, sepals, petals,stamina and pistils occours. In the third year, it's growth commences as the weather become warmer in late spring. The plants flower in May and fruit in June, and wither from September to October. The developmental process of the buds shows an adaptive mode in alpine regions.

Key words: Cypripedium flavum