Keel flowers of the Polygalaceae and Fabaceae: a functional comparison

Abstract

Although the superficial similarity between Polygalaceae and Fabaceae flowers is well known, a comparison between their recently more precisely defined ‘keel flowers’ reveals a wealth of functional congruences with regard to visual attraction, flower mechanics (interplay of fixed and mobile floral parts, presence of special contrivances such as tongue guide, foot handles, pollen cache, etc.), pollen presentation and nectar storage. Although keel flowers are principally addressed to bees, the increasingly pronounced fusion of floral parts gave rise to tubular flowers and has widened the spectrum of pollinators in the Polygalaceae. The intimate functional correspondence does not affect the assessment that the floral architecture (in terms of homologies) is quite different between the families. This is discussed with reference to the sistergroup relationship of the two families emanating from molecular systematics.