Grasses can be identified by the swollen base of each leaf where it meets the stem. This is called a ligule. There are 22 genera, important ones are listed. Most of these are emergent and rooted. Cyperaceae - the Sedge Family.
Sedges have a characteristic fruit near the tip called an achene.
They also have a small section of plant above the fruit called an involucre. These plants are emergent and rooted. Lemnaceae - the Duckweed Family. This family is free-floating, minute and found in freshwater. There are other genera that are not listed here.