Nassella, or needlegrass, is a New World genus of over 100 perennial bunchgrasses found from North America through South America. The Latin word nassa refers to "a basket with a narrow neck". It is usually considered segregate from the genus Stipa and includes many New World species formerly classified in that genus. As of 2011, The Jepson Manual includes Nassella within Stipa.

Nasella is characterized by strongly overlapping lemma margins and reduced, veinless paleae. The lemma tips are fused into the "crown", a short membrane that surrounds the base of the lemma. The rim of the crown usually has hairs.

Many species form both cross-pollinating and self-pollinating florets in the terminal panicle. The self-pollinating florets have 1–3 small anthers; the cross-pollinating florets have 3 longer anthers. Some species have self-pollinating inflorescences hidden in their basal leaf sheaths. These hidden inflorescences lack glumes and usually lack awns.

Some species (especially Nassella neesiana and Nassella tenuissima) are considered invasive pests, as the grass is not properly digested by ruminants.

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