The plants forming these prairies are generally known as eelgrass (Zostera), while in the Mediterranean Sea there are great beds of the plant Posidonia, which owes its scientific name to the Greek sea-god Poseidon. These plants form a dense prairies that may be as much as 1 metre (3 feet) in height. Thousands of individual fronds can be counted in each square metre (10 square feet). The fronds are regularly replaced and the old, shed fronds are washed up on the beach. Particularly in autumn, when the currents are stronger, these shed fronds tend to pile up on the beach. Along the Atlantic coast of Europe, eel-grass is collected at low tide, mixed with seaweeds, and used as a fertilizer.