The tallest grass is the giant bamboo (Dendrocalamus giganteus). It can grow up to 120 feet (36 meters) tall, making it the tallest grass species in the world.

Here are some other tall grasses:

* Elephant Grass (Pennisetum purpureum): Can reach heights of 15-20 feet (4.5-6 meters).

* Sugarcane (Saccharum officinarum): Can grow up to 15-20 feet (4.5-6 meters) tall.

* Miscanthus (Miscanthus sinensis): Some cultivars can grow up to 12 feet (3.6 meters) tall.

These are just a few examples, and there are many other tall grass species around the world.