Sorghum halepense, commonly called Johnsongrass, is a plant in the grass family, Poaceae

Poaceae

The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

, native to the Mediterranean

Mediterranean Basin

In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...

 region, but growing throughout Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and the Middle East

Middle East

The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

. The plant has been introduced to all continents except Antarctica and most larger islands and archipelagos. It reproduces by rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s and seeds.

Johnsongrass has been used for forage

Fodder

Fodder or animal feed is any agricultural foodstuff used specifically to feed domesticated livestock such as cattle, goats, sheep, horses, chickens and pigs. Most animal feed is from plants but some is of animal origin...

 and to stop erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

, but it is often considered a weed

Weed

A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...

 for the following reasons:

1. Foliage that becomes wilted from frost or hot dry weather can contain sufficient amounts of hydrogen cyanide to kill cattle and horses if it is eaten in quantity.
2. The foliage can cause 'bloat' in such herbivores from the accumulation of excessive nitrate
   Nitrate
   The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
   
   s; otherwise, it is edible.
3. It grows and spreads so quickly that it can 'choke out' other cash crops that have been planted by farmers.

This species occurs in crop fields, pastures, abandoned fields, rights-of-way, forest edges, and along streambanks.
It thrives in open, disturbed, rich, bottom ground, particularly in cultivated fields.
Johnsongrass resistant to the popular herbicide

Herbicide

Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...

 glyphosate has been found in Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

 and the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.