Johnson grass Sorghum ha1epense (L.) Pers., [SORHA, sorgho d'Alep, sorgho de Johnson] Perennial reproducing by seed and by large, coarse underground stems (rhizomes). Stems 50-270 cm (2 - 9 ft.) tall, 5 - 20 mm (1/5 - 4/5 in.) in diameter, smooth and stiff or wiry; leaves 20 - 60 cm (8 - 24 in. ) long, 1 - 2 cm (2/5 - 4/5 in.) wide, bright green, and smooth; leaf sheaths split with smooth overlapping margins; ligule membranous, 2 -5 mm (1/12-1/5 in.) long; no anricles; collar (junction between leaf blade and leaf sheath) often with purplish blotches on its sides; rhizomes thick and fleshy, at first white to pinkish, but turning chestnut brown over winter, as much as 1 cm ( 2/5 in.) in diameter and up to 1 m (40 in.) long, with many nodes and inter-nodes, frequently rooting from the nodes, and the internodes partially covered with brown scale-like heaths; inflorescence up to 50 cm (2 ft.) long, with whorls of upright branches; at first compact, later spreading and open; spikelets arranged in pairs at each node along the thin branches, 1 member of the pair is sterile (non-seed bearing), rather dull in texture and has a short stalk; the second member of each pair is fertile (contains the grain or 'seed"), rather plump, about 5 mm (1/5 in.) long by 2.5 mm (1/10 in.) wide, does not have a stalk, and may have a twisted awn 1 - 1.5cm (2/5 - 3/5 in.) long. Flowers from July to September.

Johnson grass is presently known to occur in 13 counties in southern and southwestern Ontario.

 Young plants of Johnson grass might be mistaken for very thin plants of corn, Sudan grass, or an annual grain sorghum. They can be distinguished from corn by the size and shape of the mother seed attached to the primary root of the seedling, or if growing as a shoot from an overwintered rhizome, by the presence of the thick, hard, brownish rhizome. Older plants can be distinguished by their large, open, non-silky inflorescences with plump seeds, and in autumn by the presence of coarse. whitish, rope-like, branching rhizomes horizontal underground stems about 1 cm (2/5 in.) in diameter in late autumn. Most rhizomes are killed by Ontario winters, but 2 or 3 stands are apparently hardy enough that their rhizomes are not killed, and these plants are acting as true perennials. Also compare with Common reed.

(Source: Ontario Ministry of Agriculture and Food, Publication 505, Ontario Weeds)