Are Hydrangea Flowers Unique?

Abstract

APART from Meconopsis betonicifolia and Hydrangea macrophylla, no plant has been recorded as displaying a flower colour change, caused by varying soil conditions. That such a plant might exist is a possibility depending on three conditions^1,2: (1) it must have a delphinidin flower pigment which in an acid cell sap is normally pink but is blue in the presence of excess aluminium; (2) it must be able to accumulate aluminium; this is a specific characteristic manifest only when sufficient is available, for example, in acid soils; (3) it must have a wide range or reaction tolerance. Many plants fulfil the first condition but invariably fail the rest. If a blue-flowered plant could be found that also accumulates aluminium, then there is a possibility that if such a plant could be grown in a neutral or slightly alkaline soil and so be unable to accumulate this element, a change of flower colour from blue to pink would take place.