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Montana Field Guide

Montana Field Guides

Johnson Grass - Sorghum halepense

Exotic Species (not native to Montana)

Global Rank: GNR
State Rank: SNA

Agency Status
USFWS:
USFS:
BLM:
MNPS Threat Rank:
C-value: 1

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General Description
Annual cultivated bunchgrass. Stems 50–100 cm. Leaves: blades 3–5 cm wide; ligules 1–5 mm long, membranous but densely covered with hairs. Inflorescence a dense panicle 10–30 (60) cm long, rachis and pedicels short hairy. Spikelets 4–9 mm long, glumes purplish at maturity. Lemmas unawned or with an awn 5–20 mm long, bent and early deciduous (Lavin in Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Diagnostic Characteristics
The distinguishing characteristics of Sorghum halapense are the ribbed leaf sheath, the conspicuous midrib, the large, purplish panicle and the extensive rhizome system. Panicum bulbosum, which has been confused with S. halapense, can be recognized by its short, knotty rhizomes and bulbous swellings at the base of the culms.

Range Comments
Sorghum halapense is a cosmopolitan weed thought to be native to the Mediterranean region (Holm et al. 1977), but with controversy over its origin. It was introduced to the United States in the early 1800s as a potential forage crop. By the end of the 19th century Johnson grass was growing throughout most of the United States (McWhorter 1981). New ecotypes have evolved allowing the species to expand its range. The common name originates from farmer Johnson who introduced it into Alabama from South Carolina in 1840 (Warwick and Black 1983).

Habitat
Cultivated mostly for forage (e.g., milo and sorgo), occasionally as an ornamental, rarely escaping (Lavin in Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

References
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Citation for data on this website:
Johnson Grass — Sorghum halepense.  Montana Field Guide.  .  Retrieved on , from