Nassella

Nassella is a genus of grasses belonging to the family Poaceae, subfamily Pooideae. These grasses are commonly known as needlegrasses. The genus is native to temperate regions throughout the world, including North and South America, Australia, and New Zealand.

Nassella species are typically perennial bunchgrasses, meaning they grow in clumps rather than spreading by rhizomes. They are characterized by their narrow, often rolled leaves and distinctive awns (bristle-like appendages) that extend from the tips of their seeds. These awns can be quite long and sharp, aiding in seed dispersal by embedding in soil or animal fur. The awns often twist and untwist in response to changes in humidity, which can also help to drive the seed into the ground.

The taxonomy of Nassella has been subject to considerable revision. Many species formerly classified within Nassella have been moved to other genera, particularly Stipa. Ongoing research using molecular data continues to refine our understanding of the relationships between different grass species and genera. As a result, the exact species composition of Nassella can vary depending on the taxonomic authority consulted.

Some Nassella species are valued as ornamental grasses in landscaping due to their attractive foliage and seedheads. However, others are considered invasive weeds, particularly in agricultural areas and natural ecosystems. Their sharp seeds can injure livestock and can outcompete native plant species. Control measures for invasive Nassella species often include herbicides, grazing management, and manual removal.

The ecological roles of Nassella species vary depending on the specific species and the environment in which they occur. They can provide forage for wildlife and livestock, contribute to soil stabilization, and serve as components of native grasslands. Their presence or absence can also be an indicator of habitat quality and disturbance.