Characterization of Hydrangea macrophylla Cultivars by the Anthocyanin Content in their Sepals

Abstract

In order to ascertain the role of anthocyanin content on the color and brightness of Hydrangea macrophylla sepals, anthocyanin contents of different colored sepals were measured for numerous commercial cultivars. Anthocyanin contents were primarily determined by extraction of the pigment, then measurement by differential spectrophotometry. Concentrations ranged from about 25 to over 400 μg delphinidin-3-glucoside per g of fresh sepal, with the magnitude roughly proportional to the perceived intensity of sepal coloration for that Hydrangea macrophylla cultivar. However, the anthocyanin content was independent of the sepal color, being the same for red, purple, or blue sepals of the same cultivar. Even though significant sepal-to-sepal variation in color intensity existed within a single inflorescence, the extractable anthocyanin content was constant for a specific cultivar. Accordingly, Hydrangea macrophylla cultivars were classified in terms of their color brightness or anthocyanin content in sepals as blush (very light colored, 25 to 60 μg·g −1 ), cold-hardy (light colored, 80 to 120 μg·g −1 ), classic (medium colored, 140 to 190 μg·g −1 ), vivid (deep colored, 230 to 270 μg·g −1 ), or vibrant (very deep colored, >300 μg·g −1 ) at peak bloom. The anthocyanin content of the sepals steadily increased as the inflorescence approached peak bloom, remained constant for a week or more, then decreased. The cultivar-dependent anthocyanin contents of the sepals can be used, in part, to rationalize the relative bluing capability of the various Hydrangea macrophylla cultivars.