Horsetail Feather Grass

S. tirsa is a perennial, tuft-forming grass with culms 40–100 cm tall. Leaf-sheaths are glabrous, ligules short (0.2–0.5 mm), and blades filiform, involute, 1–2 mm wide, puberulous and hairy beneath, with attenuate tips. The inflorescence is a contracted, linear panicle subtended at the base by a leaf. Spikelets are solitary, pedicelled, and 50–65 mm long, each with a single fertile floret and disarticulating at maturity. Glumes are lance-shaped (lanceolate), pointed (acuminate), membranous, and longer than the florets (50–65 mm). The fertile lemma is elliptic, 18–20 mm long, pubescent in lines, convolute around the inner bract (palea), and terminates in a single awn. The awn is bent twice (bigeniculate), 350–500 mm long, with a twisted column and feathery (plumose) limb. The inner bract equals the lemma in length, 2-veined. Flowers have three small scales (lodicules), three smooth-tipped anthers, and two stigmas; the ovary is glabrous. The fruit is a grain (caryopsis) with adherent outer layer (pericarp) and a linear narrow scar (hilum).

According to Plants of the World Online, Stipa tirsa is native to parts of Europe and Asia, occurring from the Iberian Peninsula eastwards to Siberia.