Sorghum halepense (L.) Pers.

Johnson Grass

© SRTurner

Family - Poaceae/Andropogoneae

Habit - Perennial, C4 (warm season) grass, with stout, long-creeping, usually white rhizomes, forming colonies.

	Rhizome.
© DETenaglia

Stems - Ascending or erect, to 2 m or more, often stout, unbranched, circular in cross section.

	Stem and leaf.
© SRTurner

	Node.
© DETenaglia

Leaves - Leaf blades 10-90 cm long, 8-25 mm wide, the midrib thickened and often whitened adaxially.

	Leaves. The central white stripe is characteristic of this species.
© SRTurner

	Leaf abaxial.
© SRTurner

	Stem and leaf sheath.
© SRTurner

	Ligule.
© DETenaglia

	Basal leaves in-situ.
© DETenaglia

Inflorescences - Dense panicles to 50 cm, the branches usually spreading at maturity, ending in small spikelike racemes with 2-6 nodes, typically with a yellowish, reddish, or yellow-brown coloration.

	Inflorescence.
© SRTurner

	Inflorescence detail.
© SRTurner

Spikelets - Glumes of the sessile, perfect spikelet 4-6 mm long, longer than the florets. Fertile lemma with the awn 8-15 mm long.

	Spikelike raceme and spikelets.
© SRTurner

	Spikelets.
© DETenaglia

Fruits - Caryopses 2-3 mm long, oblong-ovate in outline.

Flowering - June - November.

Habitat - Forest openings, streambanks, prairies, pastures, fields, roadsides, railroads, open, disturbed areas.

Origin - Native to Eurasia.

Lookalikes - Sorghastrum nutans.

Other info. - This weedy species can be found throughout much of Missouri, and throughout most of the southern half of the continental U.S. The plant is easy to identify while in flower because of its pyramidal inflorescences which have a reddish tinge. This is one of the largest and most common weedy grasses in the state. It can reach 3m tall.

S. halepense is an invasive scourge of fields, pastures, and roadsides in many parts of Missouri and elsewhere. It excludes other species by forming large, dense, rhizomatous colonies, and spreads easily both by seed and by rhizome fragments. The plant produces hydrogen cyanide under conditions of stress, and can also accumulate toxic levels of nitrate. The pollen is a cause of hay fever. Steyermark noted that the plant could be eradicated in cultivated areas by repeated deep plowing, then allowing the ground to lie fallow, and then cultivating the area with a different kind of crop. Interestingly, Johnson grass will decline or even disappear in fields which are continuously grazed, since it is grazed preferentially by cattle.

The plant referred to as Sorghum halepense in North America is probably a stable hybrid between Eurasian S. halepense and the cultivated sorghum (S. bicolor).

Photographs taken near Springfield, MO., 7-4-03 (DETenaglia); also along the Katy Trail near Dutzow, Warren County, MO, 8-20-2021, and near Labadie, Franklin County, MO, 8-22-2021 (SRTurner).