Echinochloa P. Beauv., Ess. Agrost. 53. 1812. Blatter & McCann, Bombay Grasses 147. 1935; Bor. Fl. Assam 5:242.1940; Sultan & Stewart, Grasses W. Pak. 1:43. 1958; Bor, Grasses Burma Ceyl. Ind. Pak. 307. 1960; Bor in Towns., Guest & Al-Rawi, Fl. Iraq 9:479.1968; Bor in Rech.f., Fl. Iran 70:479.1970; Tzvelev, Poaceae URSS 660. 1976; Clayton in Tutin et al., Fl. Eur. 5:261. 1980.
Annuals or perennials. Leaf-blades linear, flat; ligule absent or represented by a line of hairs. Inflorescence composed of racemes arranged on a central axis; rhachis triquetrous, scabrid, often setose, the spikelets paired (very rarely single) or on short side branchlets and forming (2-)4 or more rows. Spikelets narrowly elliptic to subrotund, convex on the back, flat on the front, ± hispid, cuspidate or awned, rarely obtuse and then the spikelet borne upon a short stipe; lower glume ovate, ± one-third the length of the spikelet, typically acute to acuminate; upper glume as long as the spikelet, acute to acuminate, rarely with a short awn-point or obtuse; lower floret male or barren, with or without a palea, its lemma resembling the upper glume but often awned; upper lemma crustaceous, smooth and shining, acute (very rarely obtuse), clasping only the margins of the palea; upper palea acute (rarely obtuse), with the tip briefly reflexed and ± protuberant bet¬ween the lemma margins. Caryopsis broadly elliptic, dorsally flattened.
A genus of about 20 species in tropical and warm temperate regions through-out the world; 5 species occur in Pakistan.
This is a difficult genus to separate from Brachiaria. The reflexed tip of the upper palea, though requiring careful dissection, seems to be the most reliable distinguishing character.
Echinochloa is taxonomically difficult, for it consists of a number of inter-grading polymorphic complexes; within each complex there are numerous micro-taxa, distinguished as much by their phenology and ecology as by their morphology. This diversity apparently springs from a tendency to self-pollination, coupled with a fluent adaptability to the wealth of ecological niches associated with seasonally wet and ruderal habitats. Little experimental work has been done on these aspects, and there is much uncertainty as to the most appropriate taxonomic treatment.
There is so much introgression between species that unambiguous key characters are hard to find. The habit, whethr annual or perennial, can be one of the most useful, but in Pakistan only Echinochloa stagnina, a floating aquatic, is not annual. Single characters (except the ligule in E. stagnina) should not be trusted implicitly but the descriptions read as a whole. Spikelet measurements exclude awns and awn-points.