Floral Sex Allocation And Reproductive Success Within Inflorescences Of An Apomictic Species, Hosta Ventricosa

The plant reproduction ecology has made remakable progress during last several decades. Especially, Sex allocation theory has become one of the most important parts in evolutionary ecology. We investigated floral sex allocation and reproductive success within inflorescences of Hosta ventricosa in Bi Feng Mountain (30°04’N,102°59’E) in Ya’an, Sichuan and Shan Wang Ping farm (29°06’N;107°19’E) in Nan chuan,Chongqing. We also explored the reason for the variation of petterns to reveal the adaptive senses of different pattterns of sex distribution within inflorescences. The results showed as follows:1. The patterns of sex allocation within-inflorescences differed in three populations of Hosta ventricosa. Comparing with basal flowers, pollen number and ovule number at distal flowers was smaller in populations Bi Feng Mountain、Shan Wangping1and Shan Wangping2respectively.These variations may be caused by the position of flowers in nonfruiting inflorescences. Pollen to ovule ratio declined from base to top in population Shan Wangping2. Pollen to ovule ratio was slightly lower in middle flowers, and higher in basal flowers in population Shan Wangping1. But differences among different flower positions was not significant. Pollen to ovule ratio was higher in middle flowers and smaller in basal and distal flowers in population Bi Feng Mountain. So,the postion of inflorescce sex allocation in Hosta ventricosa should be considered.2. The patterns of fruit set and seeds per flower within racemes of H. ventricose were various among populations under natural pollinations. Fruit set was highest in middle flowers, seeds per fruit was lowest for baseal position and seeds per flower was lowest in distal position in population Bi Feng Mountain. but seeds per fruit and seeds per flower decreased from basal to distal positions in population Shan Wangping1. Seeds per fruit varied significantly with flower position in population Shan Wangping2, but seeds per flowers was highest for middle position and lowest for distal position. It was caused by variation in the relative importance of pollen limitation and resource limitation.3. Display size per flower was consistently highest for middle position, and lowest for distal position in all populations, which was similar to fruit set.