Glyceria maxima (Hartm.) Holmb.

Tall, luxuriant, wide-leaved perennial sending up numerous long leafy shoots from a stout creeping rhizome. Leaf-sheath entire at first, later splitting, light green to pale brown, often purplish, paper-like, shining, very finely scabrid to almost smooth, with numerous conspicuous cross-veinlets. Ligule (4)–4.5–6.5 mm, firmly membranous, glabrous, blunt, but tapered centrally to fine point. Leaf-blade (20)–30–50 cm × 10–20 mm, flat, finely striate, very finely scabrid to almost smooth, abaxially scabrid above on conspicuous midrib; margins finely scabrid, tapering abruptly to short ± rigid tip. Culm (5)–10–180 cm, robust, internodes glabrous. Panicle 20–30–(40) cm, lax and open, or contracted and rather dense, broadly ovate to oblong, with numerous spikelets; rachis, branches and pedicels finely scabrid, longer branches naked below. Spikelets (5)–6–7.5–(10) mm, (3)–4–8-flowered, green, or tinged purplish brown. Glumes subequal, hyaline, 1-nerved; lower 1.7–2.5 mm, elliptic-oblong, subacute, upper 2–3.5 mm, ovate-oblong, obtuse. Lemma 2.5–3.5 mm, 7-nerved, elliptic to ovate-elliptic, broadly obtuse, subcoriaceous; nerves minutely prickle-toothed, not reaching upper hyaline minutely prickle-toothed margins. Palea oblong, keels tubercular-scabrid. Rachilla 0.7–1 mm, glabrous. Anthers (1)–1.5–1.8 mm. Caryopsis c. 1.5 × 1 mm.

[From: Edgar and Connor (2000) Flora of New Zealand. Volume 5 (second printing).]