Description from Flora of China
Arundo karka Retzius, Observ. Bot. 4: 21. 1786; A. roxburghii Kunth; Phragmites cinctus (J. D. Hooker) B. S. Sun; P. roxburghii (Kunth) Steudel; Trichoon roxburghii (Kunth) Wight.
Robust perennial from an extensive creeping rhizome. Culms very stout, often woody, 4–6 m tall, 1.5–2.5 cm in diam. Leaf sheaths greenish, glabrous; leaf blades erect-ascending, up to 80 × 2–3 cm, abaxial surface scabrous, apex stiff, long acuminate; ligule 0.5–1 mm, ciliolate. Panicle 30–50 × 10–20 cm; branches of lowermost whorl bare of spikelets toward base, ± glabrous at insertion. Spikelets 10–12 mm, florets 4–6; glumes lanceolate-elliptic, obtuse to acuminate, lower glume up to 1/2 length of lowest lemma, 2.5–4 mm, upper glume 3.5–5 mm; lowest lemma narrowly elliptic, 7–12 mm; floret callus with hairs 4–8 mm; bisexual lemmas linear-lanceolate, 8.5–10 mm, apex long attenuate. Fl. and fr. autumn. 2n = 24, 36, 38, 48.
This is a very robust species found in warm parts of the Old World. It has stiffer, more scabrous leaf blades and smaller spikelets with shorter callus hairs than Phragmites australis.
The name "Arundo vallatoria Linnaeus" (Herb. Amboin. 15. 1754) belongs here, but was not validly published and cannot serve as a basionym (see Art. 34 Ex. 2 of the Saint Louis Code). However, Phragmites vallatorius Veldkamp (Blumea 37: 233. 1992) was validly published as a superfluous illegitimate name, because it included the type of P. karka.
Warm swampy valleys and river banks; under 1000 m. Fujian, Guangdong, Guangxi, Hainan, Sichuan, Taiwan, Yunnan [Cambodia, India, Indonesia, Japan, Laos, Malaysia, Myanmar, New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; Africa, N Australia, Pacific Islands].