Floral Structure and Dynamics of Nectar Production inEchinacea pallidavar.angustifolia(Asteraceae)

Abstract

The reproductive structure of the disk florets of Echinacea pallida var. angustifolia (Asteraceae) in relation to insect pollination was investigated using light, fluorescence, and scanning electron microscopy. The study of this self‐incompatible species emphasized pollen production, pollen‐stigma interactions, transmitting tissue, and vasculature within the style. Nectary structure and nectar production dynamics were also examined. Produced in the fused anther tubes, the trinucleate pollen with yellow pollenkitt was plentiful per floret, yielding a pollen:ovule ratio of 24,130. Encircling the style base at the ovary summit, the floral nectary possessed modified stomata whose pores, as well as nonstomatal gaps in the epidermis, provided apoplastic pathways for nectar escape and reabsorption. Phloem alone supplied the gland interior, the sieve element–companion cell complexes reaching up to the nectary epidermis. Nectar was hexose dominant, its volume and nectar‐sugar quantity per floret peaking on the aft...