For Impatiens pallida in SE Pennsylvania, there were major differences in the growth form of crowded and uncrowded plants. Although they were smaller in stem diameter and had less total leaf area and branch length, crowded plants were taller than uncrowded plants. Uncrowded plants had significantly more leaf area, and this leaf area was located lower along the main axis of the plant than in crowded plants; they also had more, longer and lower branches. In uncrowded populations there was a linear relationship between the height of an individual and its total leaf area or branch length, but these relationships were curvilinear or discontinuous for crowded populations. This suggests different patterns of growth for canopy and sub-canopy individuals within crowded stands. -from Authors