Four populations of Asclepias syriaca L. (common milkweed), growing in close proximity and in linear alignment, were analyzed with regard to plant growth following organ removal. To determine if the loss of reproductive organs could eventually promote growth, all umbels were removed from plants of one population. The degree of regrowth was compared in the single treated and the three untreated populations. Both vegetative and reproductive characters were analyzed, as the umbel-excised plants produced a second set of flowers and fruits. The degree of regrowth was referred to as compensatory if development was similar in manipulated and intact plants. Decreased or increased growth in umbel-excised plants, when compared to unmanipulated plants, was referenced as under compensation or over compensation, respectively. Plants of one of the middle populations had all umbels removed and, after 39 days, manipulated and intact plants were harvested. Over compensation was exhibited in umbel-excised plants when analyzing all vegetative characters as: 1. longer stems (by 44%), 2. wider stems (by 82%), 3. greater stem mass (by 163%), 4. heavier above-ground biomass (by 191%), 5. heaviest individual leaves (by 130%), 6. heaviest average internode mass (by 135%), 7. most nodes (by 25%), and 8. heavier comparable internodes in treated plants (9 of 15). Compensatory growth was revealed in umbel-excised plants when compared to intact plants with regard to: 1. seed number per follicle (129 seeds per fruit), 2. individual fruit mass (2.7 g per fruit), and 3. individual seed mass (6.2 mg per seed). Additionally, the individual mass of interiorly and exteriorly developed seeds was not significantly different in fruits from treated or untreated plants. In conclusion, umbel-excised plants exhibited over compensation when analyzing vegetative characters, and compensatory growth when comparing reproductive features.

Key words: Asclepias, compensatory growth, herbivory, milkweed, umbel excision