Avena sterilis

Name and classification

Avena sterilis L.
(=Avena ludoviciana Durieu; Avena sterilis ssp. ludoviciana (Durieu) Gillet & Magne)
Family Poaceae, Tribe Aveneae

Common names

animated oat, wild oat

Disseminule

spikelet with or without glumes, attached pair of florets, or single floret; disarticulation above the glumes at base of lowest floret.

Description

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 considerations

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.

Similar species

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
Supplementary character information:

Avena sterilis: the back of the lowest palea is minutely hairy

Avena sativa:

  • basal scar horizontal rather than oblique as in A. sterilis and A. fatua;
  • rachilla tip jagged, pointed, and fractured;
  • scutellum outline on the caryopsis is clearly evident, whereas it is not very clear on A. sterilis and usually less so on A. fatua;
  • lemmas smooth and shiny, whereas those of A. sterilis and A. fatua are grainy or rough.

Distribution

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

Habitat

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.

General information

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 man and grazing animals. The florets are transported as an impurity in harvested cereals. The grains are highly viable.

spikelet (left), floret (middle), attached pair of florets (right)

spikelet (left), floret (middle), attached pair of florets (right)

ventral view of primary florets showing basal scars

ventral view of primary florets showing basal scars

dorsal view of primary floret bases

dorsal view of primary floret bases

primary florets with apices broken off

primary florets with apices broken off

secondary florets in ventral view

secondary florets in ventral view

secondary florets in dorsal view

secondary florets in dorsal view

pegged bases of secondary florets

pegged bases of secondary florets

caryopses in dorsal (left) and ventral (right) views; photo by Mark Thurmond

caryopses in dorsal (left) and ventral (right) views; photo by Mark Thurmond

florets and caryopsis; photo by Rodney Young

florets and caryopsis; photo by Rodney Young

spikelet, florets and caryopses; photo by Rodney Young

spikelet, florets and caryopses; photo by Rodney Young

A, spikelet with two florets; B, floret in side view; C, floret in ventral view; drawing by Lynda E. Chandler

A, spikelet with two florets; B, floret in side view; C, floret in ventral view; drawing by Lynda E. Chandler