Here are some possibilities, though they might not be widely recognized:
* Tufts of grass: This is a common term for a clump of grasses, but it doesn't necessarily encompass a whole field or meadow.
* Thicket of grasses: This term suggests a denser growth of grasses, perhaps taller than a simple tuft.
If you're looking for something more formal, you could use:
* Stand of grasses: This is a more general term, but it still conveys the idea of a collection of grasses.
* Patch of grasses: This is a more informal term, but it works well for smaller groups of grasses.
Ultimately, the best collective noun for grasses will depend on the specific context and the desired effect.