The Comparative Ecology of Impatiens capensis Meerb. (Balsaminaceae) in Central New Jersey

Abstract

To measure vegetative and reproductive plasticity, survival, growth, and reproduction of Impatiens capensis, populations were studied in eight habitats of widely varying light and soil moisture. Maximum seedling densities ranging from 73 to 2,117 m-2. Four populations lived until frost in October, but the others survived only until late July to early September. Vegetative growth showed great variability with maximum height 17. 3 ± 1.2 to 140.4 ± 4.4 cm, maximum number of nodes 6.8 ± 0.7 to 34.8 ± 0.9, and maximum weight 0.05 ± 0.006 to 68.4 ± 9.0 g plant-1. Transplants grown at a common site, however, showed only moderate differences in height (68.7 ± 4.8 to 104.6 ± 5.2 cm plant-1). Flowering extended over at least 2 mo in each population. Cleistogamous flowering began in early May for three populations, but started as late as July for two others. Chasmogamous flowers appeared in only three populations and always several weeks after cleistogamous flower production was initiated. This pattern was also seen for the transplants, but virtually all individuals produced chasmogamous flowers. Estimated annual cleistogamous flower production ranged from 83 to 119,538 flowers m-2 yr-1. Estimated maximum chasmogamous flower production was 9,569 m-2 yr-1. Successful flower production did not guarantee successful capsule production, as the most prolific flower producers converted only 22% of their flowers to capsules compared to a high of 67%. Estimated annual seed production was 35 to 17,076 m-2 yr-1. Effort put into seed production (seeds produced m-2:net aboveground production m-2) ranged from 1.7 to 45 seeds g-1 net production. The percentage of seeds that germinated ranged from 1.4 to 63.4%. Field and transplant studies showed that vegetative growth and flower production were very plastic and responsive to differences in habitat, with light being the most important controlling variable. In contrast, patterns of flowering phenology, related to the length of the growing season, suggested genetic differences between populations, reflecting the contraints set by individual sites on populations at those sites.