Flower:

Branching cluster 2½ to 9½ inches long at the top of the stem, erect or slightly nodding, the main branches more or less erect, with 1 or 2 spikelets (flower clusters) per branch. Spikelets are short to long-stalked, single-flowered, 15 to 30 mm (~½ to 1 1/6 inches) long, narrowly lance-elliptic in outline

At the base of a spikelet is a pair of bracts (glumes), both similar, thin, hairless, 15 to 30 mm long, longer than the floret, narrowly lance-shaped with a long taper to a pointed tip. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thicker than the glumes, 5-veined, 8.5 to 14 mm long, unevenly covered in brown hairs especially on the lower half, densely hairy along the edges, narrowly lance-oblong with a stiff awn 2 to 4 inches long and a ring of short hairs around its base; the palea is about as long as the lemma and mostly hidden by it. The thickened base of the floret (callus) is 3 to 5 mm long and covered in straight, brown hairs.

Leaves and stems:

Leaves are basal and alternate on the lower stem, 1.3 to 3 mm (~1/8 inch) wide, hairless. Sheaths are hairless. The ligule (membrane where the leaf joins the sheath) on lower leaves is up to 1 mm long, straight or rounded across the top, often higher on the sides than the middle, minutely fringed across the top; upper nodes are up to 3.5 mm long, pointed to rounded to straight across. Nodes are smooth, occasionally evenly covered in short hairs, and are mostly hidden within the sheaths. Stems are erect and hairless.

Fruit:

At maturity, glumes turn pale and florets medium to dark brown, the florets shedding individually, leaving the glumes behind on the stalk. The floret base has a needle-like point and the stiff hairs on the surface cause it to attach to anything unlucky enough to pass by. The long awn twists in response to changes in moisture, coiling and uncoiling as it dries, bent once or twice above the spirally twisted base, and eventually drills it into the ground. Grains (seeds) are light brown, linear.

Notes:

Western Porcupine Grass, known in some references as Nassela curtiseta or Stipa curtiseta, was first documented in Polk County in 2019, and makes Minnesota the new eastern edge of its US range. It is much more common in Canada, where it's found in dry, open grassy areas of the plains and montane zones. The DNR currently tracks it and it will likely be designated Special Concern in Minnesota the next time they update the official rare species list.

There are 3 Hesperostipa (formerly Stipa) species currently known to be in Minnesota, all of which can (and do) grow side-by-side in the same kinds of habitat and are best distinguished when mature, so the size and shape of awns are easily seen. Most similar is Hesperostipa spartea (Porcupine Grass), generally a larger, more robust plant with awns up to twice as long H. curtiseta, its lower nodes usually have lines of fine hairs and lower sheaths are usually fringed along the edges. H. comata (Needle-and-thread Grass) has curling awns, lemmas evenly covered in whitish hairs, and may have short awns on the glumes. Later in the season after florets drop off, the length of persistent glumes combined with ligules, lower nodes and sheaths may help distinguish these three.

Of note is many references state the lower ligules of H. curtiseta are higher on the sides than the middle. While this may frequently be true, my own experience noted the shape can be variable but the minute fringe across the top was pretty consistent. Magnification is required for this as well as the hairs on nodes and sheaths of H. spartea.