Locoweed - History and Etymology

History and Etymology

The first technical account (in English) of locoism was published in 1873, in the United States. Linguists have documented locoism in use among English speakers by 1889, and both loco and locoweed in use by 1844.

Loco, a loanword from Spanish, is understood by most English-speaking users in the sense of crazy, and this appears to have also been the sense understood by vaqueros. In Spanish, however, loco has an older, different sense. In Spain, where the native Astragalus species are not known to cause locoism, for centuries loco has been applied to some of these species in the sense of rambling: common names include yerba loca (hierba loca; rambling herb) and chocho loco (rambling lupine).

Locoweed is a compound of loco and weed. Although some authors claim it is incorrect to use loco as a noun (in place of locoweed), this usage has a long history.

The presence of a toxin in locoweed was demonstrated in 1909. Initially, the toxin was reported to be barium, but that was soon disproved. Swainsonine, first isolated from Swainsona, was shown to be responsible for pea struck in 1979, and was reported in both Oxytropis and Astragalus in 1982.

Since 1982, swainsonine has been isolated from still more plants, some of which also are reported to cause locoism or medical conditions similar to locoism. The first report of locoism in South America, involving Astragalus pehuenches, was published in 2000.