Carbohydrate Cycle of Plantago insularis var. Fastigiata, a Winter Annual from the Sonoran Desert

Carbohydrate content during the life cycle of Plantago insularis was determined at seven different phenological stages. As a percentage of alcohol-insoluble dry weight, carbohydrate was maximum very early in the life cycle and continually declined to a minimum at fruit set. As an absolute amount, in milligrams per plant, carbohydrate increased gradually until the cotyledons plus first- and second-leaves stage and then increased sharply to a peak at the preflowering stage. From the preflowering to the flowering stage at floral bud opening, the amount of carbohydrate rapidly decreased to a minimum. From the flowering stage to fruit set, the amount of carbohydrate sharply increased to a maximum at fruit set. This carbohydrate balance may represent adaptations to a desert environment.