Oats & Oat-grasses
What are they?
This page covers two groups of grasses - the true oats in the genus Avena and a small number of species from other genera that have a similar appearance and are known as oat-grasses. In general terms, these species share a similar appearance in their florets, which have relatively large, elongated lemmas with long, bristly awns. The florets tend to open very widely at anthesis, too, which can also give them a distinctive appearance.
Where are they found?
The true oats are typically species of cultivated and disturbed ground, with one species grown as a crop. Oat-grasses are mostly plants of established grassland, especially on chalky soils.
Identification
Click here for help with some of the terminology used on the grass pages. Oat-grasses are generally fairly easy to tell apart with attention to their overall appearance and to the flowers. The oats can be difficult to tell apart, though most species are rare or no longer present in our region, leaving two species that can be separated easily by the presence or absence of awns on the lemmas. As with many grasses, the oat-grasses may require some measurements to be taken of flower parts but, with a little more familiarity with the species, they can often be identified relatively easily by their overall appearance.
False Oat-grass Arrhenatherum elatius
A native perennial, common to abundant in many kinds of grassy places and often forming continuous cover for many miles along main roads, hedgebanks and on coastal floodbanks and similar places. Flowers June to August. Plants 50-180cm in height, loosely tussock-forming. Leaf blades 4-10mm wide, hairless or slightly hairy beneath, flat and pointed. Leaf sheaths rounded, usually smooth but sometimes a little hairy. Ligule membranous, short, rounded at the tip. Flower spike narrow when young, spreading at anthesis and becoming very narrow and upright with age. Spikelets 7-11mm with usually 2 florets (occasionally up to 5). Lower lemma 8-10mm with a 10-20mm awn, upper lemma shortly awned or awnless.
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Yellow Oat-grass Trisetum flavescens
A native perennial, common in many kinds of grassy places, especially old commons and roadsides, on all but the most acidic soils. Flowers May to July. Plants 20-100cm in height, loosely tussock-forming. Leaf blades 2-10mm wide, variably hairy or hairless, flat and pointed. Leaf sheaths rounded, the lower ones often hairy. Ligule membranous, 0.5-2mm, rounded at the tip. Flower spike narrow when young, spreading at anthesis and becoming narrow and upright again with age. Spikelets 5-7mm with 2-4 florets. Lemmas 4-5.7mm with a 2.5-9mm awn arising from or near the middle of the back. A delicate and graceful grass, often forming extensive colonies of stems and developing a rich, yellow-straw colour.
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Downy Oat-grass Avenula pubescens
A native perennial that favours chalky soils. Scattered thinly across the region but quite common on poorer soils in Breckland and Cambridgeshire. Flowers May to July. Plants 30-100cm in height, loosely tussock-forming and with short rhizomes. Leaf blades 2-6mm wide, variably hairy or hairless, flat and pointed. Leaf sheaths rounded, the lower ones densely hairy. Ligule membranous, 2-8mm, pointed at the tip. Flower spike very open and delicate. Spikelets 10-17mm with 2-4 florets. Lemmas 9-14mm with a 12-22mm awn, twisted at the base and arising from or near the middle of the back.
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Meadow Oat-grass Helictochloa pratensis
A native perennial that favours shallow, chalky soils. Scattered thinly across the region but quite common on poorer soils in Breckland and Cambridgeshire. Flowers June to July. Plants 30-80cm in height, densely tussock-forming. Leaf blades 1-5mm wide, bluish-green, rough margined, more or less hairless, flat and blunt-tipped. Leaf sheaths hairless. Ligule membranous, 1-5mm, pointed at the tip. Flower spike compact and upright at first, becoming open and sreading at anthesis. Spikelets 11-28mm with 3-8 florets. Lemmas 10-17mm with a 12-22mm awn, twisted at the base and arising from or near the middle of the back.
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Wild Oat Avena fatua
An ancient introduction from southern Europe. A common annual of arable farmland found throughout East Anglia. Flowers June to September. Plants 30-150cm in height, loosely tussock-forming or stems solitary. Leaf blades 3-15mm wide, flat, rather rough and pointed. Leaf sheaths rounded, the lower ones often hairy. Ligule membranous, up to 6mm in length, rounded at the tip. Flower spike very open, with long side branches. Spikelets 18-30mm with 2-3 florets. Lemmas 14-20mm with a 2.5-4mm, bent and twisted awn arising from or near the middle of the back. Seedheads break up readily, with each seed bearing a rounded callus at the base, where it was attached to the stem. A graceful grass, with the largest of grass flowers, making them useful for study when learning the flower parts of grasses.
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Common Oat Avena sativa
An ancient introduction from southern Europe and once widely grown as a crop, but now far less commonly grown and only occasionally found as a crop remnant or from birdseed. Flowers July to September. Plants 30-150cm in height, loosely tussock-forming or stems solitary. Leaf blades 4-15mm wide, flat, rather rough, hairless or with marginal hairs. Leaf sheaths rounded, smooth. Ligule membranous, toothed. Flower spike very open, with long side branches. Spikelets 17-30mm with 2-3 florets. Lemmas 12-25mm, typically not awned or occasionally with an awn only on the lowermost lemma. Seedheads breaking up late, with each seed not bearing a rounded callus at the base, where it was attached to the stem.
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