The staminal column in Solanum pollination: important in attraction, essential as a landing platform

Abstract

The staminal column-corolla association in solanums constitutes a floral pattern that is distinctive, and generalized across a number of genera and families – characterized as ‘solanum-type’ flowers. We conducted experiments in natural populations of Solanum xanti in California, USA, to test the structure-function of the solanum staminal column and corolla. We excised the corolla of some flowers, the stamens of others, and painted stamens of others to assay pollinator response to changes in visible and UV patterns. Acrylic-painted staminal columns were yellow like the original anther color or concolorous with the corollas, and reflected light in the UV range instead of absorbing it. The flowers with stamens excised or with paint-altered UV patterns showed significantly lower fruit set, including those painted yellow. Experimental flowers with staminal columns only, i.e. with excised corollas, set fruit at the same rate as control flowers. Thus, the bee pollinators visit experimentally-altered flowers; they do not simply avoid aberrant flowers. While the combination of stamens and corolla are undoubtedly important visual attractants, our experiments support the underappreciated, and essential, role of the staminal column as a scaffold for the common, but distinctive, ‘buzz’ pollinators of solanums.