The relationship of light and plant geometry to self-thinning of an aquatic annual herb, Murdannia keisak (Commelinaceae).

Self-thinning was examined in shaded and unshaded populations of Murdannia keisak (Hask.) Hand.-Mazz. (Commelinaceae). Four mathematical descriptions of self-thinning were compared: (1) the traditional - 3/2 thinning rule in which mean plant biomass is regressed on density; (2) principal components regression of mean plant biomass and density; (3) total stand biomass regressed on density, and (4) principal components regression of total stand biomass and density. Most slopes conform to the expected ones; however, confidence intervals reported here and in the literature are wide which may reduce the ecological value of the thinning line per se. In addition, plants grown in full sun form significantly fewer branches than those in shade. This difference in geometry results in differences in mean plant volume, in plant packing, and thus, in different thinning trajectories.