The roots of selected members of the Nymphaeaceae, Cabombaceae, and Nelumbonaceae were examined to determine root cortex characteristics in order to distinguish among the families. Each family has a characteristic root cortex structure. Members of the Nymphaeaceae typically have an endodermis with Casparian bands only, an extensive, hexagonally patterned aerenchyma with branched sclereids spreading from semi-regular hexagon cells and with transverse diaphragms, and a multiseriate hypodermis composed of a uniseriate exodermis with Casparian bands and suberin lamellae and with cellulose-thickened cell walls in some species. The Cabombaceae have small roots with an endodermis with Casparian bands and suberin lamellae, a simple aerenchyma without sclereids or transverse diaphragms, and a uniseriate exodermis with Casparian bands and distinctive suberin lamellae. The Nelumbonaceae have an endodermis with Casparian bands, suberin lamellae, and secondarily lignified cell walls, a hexagonally patterned aerenchyma without sclereids or transverse diaphragms, and a multiseriate hypodermis with a uniseriate exodermis of Casparian bands and suberin lamellae and an inner hypodermis with distinct patterns of lignified cell walls.

Key words: aerenchyma, endodermis, exodermis, lotuses, root cortex, water lilies