Flower:

Branching cluster 4 to 10 inches long at the top of the stem, sometimes erect but typically nodding, the main branches ascending to arching, with 1 or 2 spikelets (flower clusters) per branch. Spikelets are short to long-stalked, single-flowered, 30 to 40 mm (~1 to 1½ inches) long, narrowly lance-elliptic in outline.

At the base of a spikelet is a pair of bracts (glumes), both similar, thin, hairless, 5 to 7-veined, 30 to 40 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, 13 to 25 mm long, unevenly covered in brown hairs especially on the lower half, densely hairy along the edges, narrowly lance-oblong with a stiff awn 4 to 8 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 3.5 to 6 mm long and covered in straight, brown hairs.

Leaves and stems:

Leaves are basal and alternate on the lower stem, 1.5 to 4.5 mm (to 1/6 inch) wide, basal leaves up to 2 feet long, stem leaves to 12 inches long, hairless on the lower surface, usually rough and minutely hairy on the upper surface, the edges often rolled in (involute). Sheaths on lower stem leaves usually have a fringe of short hairs along the edges, the upper sheaths hairless. The ligule (membrane where the leaf joins the sheath) on lower leaves is up to 3 mm long, usually rounded or straight across; upper leaf ligules are up to 7.5 mm (~1/3 inch) long and more ragged across the top edge. Nodes are mostly smooth, or the lower nodes with vertical lines of hairs. Stems are smooth in the lower plant, becoming rough and somewhat hairy in the upper.

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, 3.5 to 6 mm long.

Notes:

It can genuinely be a miserable experience to hike through a prairie full of Porcupine Grass when it is shedding its seed. Poke, poke, poke! There are 3 Hesperostipa (formerly Stipa) species currently known to be in Minnesota; of these 3, only H. spartea has nodes with lines of hairs and lower sheaths with a fringe of hairs (magnification required). Hesperostipa curtiseta (Western Porcupine Grass) is most similar but overall smaller and less robust, the glumes, lemmas and awns all about half to 2/3 as long, and its lower ligules are often higher on the sides with a minute fringe of hairs across the top. H. comata (Needle-and-thread Grass) is also generally smaller and less robust, 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, nodes and sheaths may help distinguish these three.