Reproduction in Polemonium: Assessing the Factors Limiting Seed Set

Abstract

Evidence of pollen and/or resource limitation of seed production in the herbaceous perennial plant Polemonium foliosissimum was investigated. Large numbers of open flowers on selected individuals were hand-pollinated at regular intervals, and seed set was compared with that of control blossoms on those same plants as well as with that of control flowers on control individuals. Experimental and control individuals were monitored and reproductive output measured during the following flowering season as well. Although hand-pollinated flowers set significantly more seeds than did either set of control blossoms, the results suggest that individual reproduction (i.e., the total number of seeds produced by a plant) was limited by resources other than pollen. Pollen availability may also have limited seed production, but to a lesser extent. A proper protocol for examining the limitation of seed set is developed, and the biases inherent in most of the simplified procedures currently in use are discussed.