Nassella

Nassella is a genus of grasses in the family Poaceae, commonly known as needlegrasses. It belongs to the tribe Stipeae. The genus has undergone taxonomic revision in which several species previously placed in Stipa have been reassigned to Nassella; as a result, different authorities may treat Nassella as a distinct genus or as part of Stipa. This has led to changes in species names such as Nassella tenuissima, formerly Stipa tenuissima.

Nassella species are native to the Americas, with greatest diversity in North and South America. They are perennial, mostly bunchforming grasses that inhabit a variety of habitats including grasslands, prairies, chaparral, and open woodlands. They are characterized by narrow leaves and tall flowering stems bearing dense inflorescences. The spikelets are typically equipped with long, persistent awns, which in many species give the seed a needle-like appearance and aid in dispersal.

Ecology and uses: Nassella species play important roles in native ecosystems, including soil stabilization and providing habitat for wildlife. Some species are valued in ornamental horticulture for their fine texture and drought tolerance; Nassella tenuissima, for example, is popular in garden plantings. Other species have become problematic when introduced outside their native range; notable examples include Nassella trichotoma (serrated tussock), an invasive weed in several regions such as Australia.

Overall, Nassella represents a historically taxonomically complex group of needlegrasses with ecological significance in native habitats and diverse applications in restoration and horticulture.