hydrocharideæ

from The Century Dictionary.

• A natural order of monocotyledonous aquatic herbs, with diœcious or polygamous regular flowers on scape-like peduncles from a spathe, and simple or double floral envelops, which in the fertile flowers are united into a tube, and cohere with the 1- to 3-celled ovary; stamens 3 to 12, distinct or monadelphous; stigmas 3 or 6; fruit ripening under water, indehiscent, and many-seeded.