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Avena fatua L.

Kingdom: Plantae Rank: Species Parent: Avena Status: Valid

Common Names:

  • WILD OAT - English, United States of America
  • OAT GRASS - English, United States of America
  • POOR OAT - English, United States of America

Morphological Description

Diagnosis: Spikelets 18–32 mm long; florets usually 2(–4), if more than 2, then the uppermost typically reduced and sterile lemma awns conspicuous and geniculate, those of the upper and lower florets subequal.

Awn of lemmas geniculate, mostly 2.5–4.2 cm long; lemmas with stiff, usually reddish brown hairs on dorsal surface; florets disarticulating from the glumes.


Ecology: This species has been introduced into the United States and is considered a noxious exotic.

Notes: Roadsides and other disturbed areas, abundant in some places; Brazos and Nacogdoches (BRIT) cos.; scattered in e 1/2 of TX; throughout most of Canada and most of the U.S. Mostly Apr–May. Native to Europe and c Asia. The pointed callus of the fruit is reported to cause mechanical injuries to livestock (Burlage 1968). This taxon is considered by some sources to be among the world’s worst weeds (e.g., Holm et al. 1977). It is referred to as “the most serious annual weed of cultivated fields in the prairie provinces of Canada” (Sharma & Vanden Born 1978) and is considered to be a noxious weed in OK (Kartesz 1999). However, in other areas it is used for hay, as a range grass, and in animal feed. It is thought to have been “introduced into North America by early European settlers as impurities in seeds and feed” (Sharma & Vanden Born 1978). Material of A. fatua was found in a California mission in an adobe brick thought to have been made about 1805–1813, thus showing its introduction by early Spaniards (Hendry & Kelly 1925). This species hybridizes with A. sativa. According to Baum (ined.), the “hybrids resemble A. sativa, but differ in having the fatua-type lodicule; some also have a weak awn on the first lemma.” The taxonomy of this and the following species is controversial. The two have been treated as either varieties of A. fatua (e.g., Correll & Johnston 1970; Jones et al. 1997; Yatskievych 1999; Hatch 2002) or separate species (Sampson 1954; Diggs et al. 1999; Kartesz 1999; Baum ined.), and the level at which to recognize them seems somewhat arbitrary. It can be argued that since A. fatua is apparently involved in the ancestry of A. sativa (Zohary & Hopf 1994), recognition at the level of variety or subspecies is most appropriate. However, there is little agreement among taxonomists about the appropriate rank to use in the case of cultivated species and their ancestors— some authorities use varieties, others subspecies, yet others species. We are following Baum (ined., in the forthcoming Flora of North America treatment), the recognized North American authority on the genus, in treating the two Avena taxa at the rank of species. (fatua: false or foolish, without value)