The Inflorescence as a Metapopulation of Flowers: Position-Dependent Differences in Function and Form in the Cleistogamous Species Collomia grandiflora Dougl. Ex Lindl. (Polemoniaceae)

Investigators utilizing a metapopulational approach to study plant growth and form often assume that position-dependent effects are negligible. We have specifically examined the relationship of form and function to the position of Collomia grandiflora flowers within the apical head of the inflorescence, describing the cleistogamous (CL) and chasmogamous (CH) flowers as separate populations of parts within the inflorescence. For plants grown under uniform conditions, CL flowers are produced in positions 1-6 of the apical head; a transition to CH occurs in positions 7-14; and only CH flowers are produced beyond position 14. CL flowers show a decrease in spontaneous autogamous seed set beyond position 8; spontaneous seed set is uniformly low for CH flowers. Likewise, position-dependent variation was discovered for corolla length and anther length in both CL and CH flowers. Anther number was an unstable character over CL positions 1-3 but was stable in other positions of CL and CH flowers. CL and CH flowers behave as separate populations with respect to form and function and also are frequently internally heterogeneous over positions.