Hydrocharitaceae
Partially or wholly submerged herbs, sometimes marine Hydrocharitaceae
Fresh water plants
Leaves cauline, opposite or whorled, on elongated occasionally branched submerged stems with adventitious roots. Flowers unisexual, axillary
Leaves with entire or minutely denticulate margins. Styles in female flowers lobed or notched
Leaves in whorls of 3 very rarely 4 Elodea
Leaves in whorls of 4–6 Egeria