Floral color change in Errazurizia megacarpa, a sonoran desert shrub

Abstract

Flowers of many species undergo partial or complete color changes in the course of their development. These changes are thought to cue pollinators to receptive flowers. In the Lower Sonoran Desert of northern Mexico, individuals of the long-lived perennial shrub, Errazurizia megacarpa (S. Watts) I.M. Johnston 1924 (Leguminosae), produce many hundreds of racemose inflorescences in which the terminal, younger flowers have yellow corollas, while lower, older flowers have red ones. I studied the response of visitor species to the floral display of E. megacarpa by direct observation of visitor activity and by manipulating the floral display to remove yellow or red flowers. Equal-sized plants with similar sized floral displays containing only red flowers, only yellow flowers, and control plants with both red and yellow flowers, attract roughly equal numbers of putative pollinating insects. However, once pollinators have approached a plant, they discriminate against red flowers, visiting these extremely rarely. Floral color change in this species provides a cue to direct pollinator activity to receptive and rewarding flowers. Key words: floral color change, pollinator cues, reproductive ecology.