Colour change of petals in Malvaviscus arboreus flowers

Colour changes in the petals of two varieties of the tropical plant species Malvaviscus arboreus were investigated. The light absorbance of living petals and the absorbance of petal-extracts were measured. A separation of pigments by means of paper chromatography was attempted. Older stages of living petals show a low absorbance at all wavelengths compared with younger ones, and also a shift of the minimum at 440 nm and the maximum at 520 nm towards higher wavelengths. Petal extracts of different stages also have a different absorption spectrum; nonnectar producing flowers show a maximum at about 515 nm while nectar producing ones have merely a shoulder at 515 nm which may be due to a loss of red pigments. This loss is clearly demonstrated by paper chromatography and coincides with the beginning of nectar production. Hummingbirds, the main visitors of Malvaviscus, probably use this colour-shift for recognizing nectar producing flowers.