Avena sterilis L.
(=Avena ludoviciana Durieu; Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne)
Family Poaceae, Tribe Aveneae
animated oat, wild oat
Spikelets laterally compressed, 20–50 mm long, of 2–5 fertile florets. Glumes similar, as long as spikelet, membranous, 7–11 nerved, gaping. Florets fall together as a unit, 15–40 mm long. Lemma coriaceous, rough, 7–nerved, apex 2–toothed, with dorsal awn attached below middle of lemma; awn twisted, geniculate, 30–90 mm long; lowest palea with minute prickles on back. Floret with bearded callus; hairs to 1/5 the length of the lemma. Only primary (basal) floret with elongated, scoop-shaped scar. Rachilla tends to break off near base, so most of it is attached to base of next floret.
Identification of and differentiation among disseminules of A. fatua, A. sativa, A. sterilis, and the homozygous and heterozygous fatuoids, is notoriously difficult. This is particularly the case because florets are often found damaged in commercial seed lots from milling. As a result, a number of the characters listed below may not be seen. For example, hairs may be rubbed off, or awns and bases and apices of florets may be broken off, making determination of length and awn placement difficult. In this condition, identification of disseminules may be difficult to impossible.
An important character to emphasize is that A. fatua disarticulates above the glumes and between the florets (the only Avena species that does), so that most florets have distinctly shaped basal scars and intact rachillas. In A. sterilis, only the basal floret will disarticulate and have a distinctly shaped basal scar. The rachilla extending apically from the ventral side of the basal floret breaks off at or near its base and remains attached to the secondary floret as a pegged base; the basal floret lacks a distinct rachilla segment.
Avena fatua L. (non-FNW)
Avena barbata Pott ex Link (non-FNW)
Avena sativa L. [no image provided] (non-FNW)
The following table highlights morphological differences between A. sterilis and A. fatua.
|Character||Avena sterilis||Avena fatua|
|disarticulation||above glumes, below basal floret only; florets may be found as attached pairs||above glumes and between florets; florets almost always found singly|
|florets per spikelet||2–5||2–3|
|awn length||3–8 cm||3–4 cm|
|awn attachment||below middle of floret||above middle of floret|
|floret length||in general longer and wider than A. fatua , 15–40 mm (usually 20–25 mm)||in general shorter than A. sterilis, 14–20 mm|
|rachilla tip shape||flare-shaped (secondary and tertiary florets only)||rounded-triangular, diamond-shaped (all florets)|
|basal scar shape||elongated, scoop-shaped, longer than A. fatua (basal floret only); other florets fractured||horseshoe-shaped, sucker-mouthed (all florets)|
|callus hairs||to 7.5 mm long (1/5 length of lemma)||to 5.5 mm long (1/4 length of lemma)|
|caryopsis shape||oblong, depression caused by awn on embryo side starts below the middle of the caryopsis||long, narrow, depression caused by awn on embryo side starts above the middle of the caryopsis|
Avena sterilis: the back of the lowest palea is minutely hairy
temperate regions of southern Europe, northern Africa and southwestern Asia, including the Arabian peninsula and the Indian subcontinent; also in Ethiopia, Kenya, South Africa, and Australia; in the western hemisphere: Argentina, Costa Rica, Ecuador, Mexico, Peru, Uruguay, United States
native to the Mediterranean
warm-temperate regions in deep, fertile soils to sandy soils, flooded paddy fields, rocky hillsides up to 2000 m elevation; a weed of cereal fields, olive groves, vineyards, waste places
Avena sterilis is an annual grass, to 180 cm tall, that has been considered a valuable pasture plant but is now a serious weed of cultivated cereals. It is primarily transported by humans and grazing animals. The florets are transported as an impurity in harvested cereals. The grains are highly viable.