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FOC | Family List | FOC Vol. 22 | Poaceae | Coix

2. Coix aquatica Roxburgh, Fl. Ind. 3: 571. 1832.

水生薏苡 shui sheng yi yi

Coix gigantea Roxburgh (1832), not Koenig (1788); C. gi-gantea subsp. aquatica (Roxburgh) Bhattacharya; C. gigantea var. aquatica (Roxburgh) Watt; C. lingulata Hackel.

Perennial, aquatic. Culms creeping and rooting from nodes at base, sometimes floating, up to 30 m long, ca. 1 cm in diam., flowering stems up to 2 m tall, more than 10-noded. Leaf sheaths smooth, glabrous or upper sheaths tuberculate-hispid; leaf blades narrowly to broadly linear, up to 100 × (0.3–)1–2.5 cm, hispid with tubercle-based hairs on both surfaces or almost glabrous, midvein stout, base rounded, margins scabrous, apex slenderly acuminate; ligule ca. 1 mm, margin ciliate. Male raceme 2.5–7 cm, drooping, spikelets mostly in triads, closely imbricate; utricle ovoid, longer than broad, bony, shiny, 10–14 × 5–7 mm, white or pale brown, sometimes with a median transverse line, apex occasionally extended into a green blade. Male spikelets broadly elliptic, 8–12 mm; glumes many-veined, lower glume winged on keels, wing (0.4–)0.7–1.2(–1.5) mm wide, margin ciliolate; anthers 4–5.5 mm. Fl. and fr. Aug–Nov. 2n = 10, 20, 40.

Lakes, streams, marshy borders, open water; 500–1800 m. Guangdong, Guangxi, Yunnan [Bangladesh, Bhutan, India, Malaysia, Myanmar, Sri Lanka, Thailand, Vietnam].

All forms of the variable, perennial, aquatic Coix are included here in a single species. Some forms with a supposedly non-creeping habit have been separated as C. gigantea Roxburgh (1832), but this name is a later homonym of C. gigantea Koenig (1788), a different grass now placed in Chionachne. It is, in any case, very uncertain whether this difference in habit, which is usually impossible to determine in herbarium specimens often lacking the basal parts, is real or simply a response to the environment.

This species covers a range of chromosome levels. A form with very narrow leaf blades is the basis of Coix lingulata. Similar narrow-leaved specimens have been shown to have a chromosome number of 2n = 10. The utricle apex is sometimes extended into a leaflike, green blade. The occurrence of this feature is sporadic, and it can vary from a minute vestige to a blade ca. 3 cm or more long, even on the same plant. The leaf blades are often spotted with tubercles, which appear to be glandular and carry a short bristle-hair. These tubercle-hairs vary from dense to very sparse. The male spikelets are tightly packed into a conelike raceme, and are on average broader with broader marginal wings than in C. lacryma-jobi, but there is much variation.


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