Grasses can be annual or perennial. The roots of grasses are fibrous, which makes them good soil binders and the reason they are planted for erosion control. Grass stems are called culms. These are usually hollow, except at the nodes. Branches that originate from near ground level are tillers.
Many grasses have a rhizome, stolon, etc.
Typically alternate and in one plane. The sheath is usually not fused around the stem, but rather is open. The ligule is a small tissue found between the blade and sheath. It can be hairy, membranous, even absent, and is important taxonomically. The petals and sepals are absent, reduced to lodicules.