Ivy (Hedera helix L.) Flower Nectar and Nectary Ecophysiology

The nectary of Hedera helix is situated above the inferior ovary and completely exposed to the external environment. It consists of parenchyma containing chlorophyll overlying vascular bundles with xylem and phloem. The nectar exudes from stomata. Nectary color varied from green to brown during the flowering period (mid-September to early November). This change in color resulted from accumulation of anthocyanins in subepidermal layers of the parenchyma. Quantitative differences were observed in the photosynthetic pigments of nectaries and leaves. Their quantitative variations, associated with variation in environmental parameters (temperature and rainfall) during flowering, were different in the two organs: the quantity of photosynthetic pigments increased in leaves at the end of flowering, whereas an increase principally in b-carotene was observed in nectaries, suggesting that the nectary protected the inferior ovary from sunlight. Nectar was produced in greater abundance but with lower sugar concentration at the start of flowering, but the total quantity of sugars it contained did not vary significantly during flowering. The relative concentration of sugars showed slight variations that were not associated with significant changes in pollinators, which were mainly bees and flies.