Seed dispersion by water. Hydrochoric plants usually live on the sea shore, near rivers, lakes or pounds. They produce floating fruits or seeds that are carried away by water currents, germinating when it hits an apropriated spot.
Examples of hydrochoric plants are Coconut palms (coconuts float long distances using sea currents and germinate when they reach a beach), some of the Amazonic Lecythidaceae species (big and heavy, but very low density fruits travel down the rivers, releasing the seeds afterwards), and mangrove plants. Some genuine aquatic plants, like Water Hyacinth, depend on it sometimes, but curiously not always.