Ischæmum rugosum, Salisb.
This is an erect annual grass with tufted, leafy, compressed stems varying in length from 10 inches to 2 feet.
The leaf-sheath is glabrous, loose and compressed, with a membranous auricle confluent with the truncate ligule. Nodes usually glabrous but sometimes also puberulous.
The leaf-blade is narrow, linear-lanceolate, flat, base contracted, flaccid, acuminate, rounded at the base, glabrous or sparsely hairy on both the surfaces; the topmost leaf is often reduced to an inflated sheath enclosing the inflorescence partially.
Fig. 132.—Ischæmum rugosum.
1. A part of the raceme showing sessile spikelets with reduced pedicelled spikelets; 2. a sessile spikelet and a well developed pedicelled spikelet; 3. a reduced pedicelled spikelet; 4, 5, 6 and 8. the first, second, third and the fourth glume of the sessile spikelet; 7 and 9. palea of the third and fourth glumes of the sessile spikelet; 10. ovary.
The racemes are usually two, erect, fragile, 1 to 3 inches long with a slight thickening of the peduncle below the inflorescence; the joints are 1/3 to 2/3 as long as the sessile spikelets; trigonous and subclavate, and with long hairs on one side. The spikelets are linear-oblong, glabrous or villous, 1/8 to 1/4 inch long, sessile and stalked spikelets close together; the pedicel of the stalked spikelet is thick about 1/3 or less than the length of the sessile spikelet, ciliate on one side, confluent with the thick callus of the sessile spikelet, which is sparsely bristly. The sessile spikelet consists of four glumes and is awned. The first glume is concave, pale yellow, shining and cartilaginous to about 2/3 its length from the base, and the upper third is membranous, dimidiately ovate; at the back in the cartilaginous portion, there are three to six deep convex smooth ridges running across the glume; the membranous tip is thin and with anastomosing green veins; the margins of this glume are thick, narrowly incurved, ciliolate, and with a narrow wing on the outer margin. The second glume is oblong-lanceolate or lanceolate, coriaceous, acuminate, scaberulous, keeled and laterally compressed and on the keel just below the tip there is a narrow ciliate wing. The third glume is ovate-lanceolate, hyaline, acuminate 1- to 3-veined, male or empty, with a narrow hyaline palea. The fourth glume is shorter than the third, deeply cleft into two lanceolate acute lobes, 3-veined at the base; awn up to about 2/3 inch long; palea is linear lanceolate. Stamens are three and lodicules are small and cuneate.
The pedicelled spikelet is very variable. It is shorter than the sessile, with obscure transverse ridges and may consist of four glumes, but without an awn to the fourth glume; sometimes this spikelet is reduced to a single glume.
The grain is broadly oblong, brownish and compressed.