Grasses: Acid Heaths
What are they?
This page aims to make the identification of grasses a little easier by bringing together the commoner species that are likely to be found in a particular habitat. This should help you to learn the more likely species that you will come across, though it should always be remembered that occasional individuals of other species may turn up in unexpected places from time to time.
Where are they found?
These species are found in open habitats on acid soils. These are the grasses that can be found on heathland, typically growing as open swards between stands of heather and gorse, or on more stable areas of sandy soil in coastal dune habitats. Some species are very specific to such habitats, such as Heath-grass and Mat-grass and are thus rather scarce in East Anglia (as this is a rather localised habitat in our region), while others can be abundant on heathland but also found elsewhere - such as Common Bent.
Identification
Identifying grasses successfully requires at least a basic knowledge of the plant parts and thus it's useful to know the names of these parts (it's much easier mentioning lemmas and glumes if one doesn't have to describe where they are every time!) To assist in this, you can click here to reference a page that gives details of these features. A good rule of thumb when working through the identification of any plant is to work from bottom to top with the whole plant and from outside to the middle with the flower parts (so - root, stem, leaf, flowers... sepal, petal, stamen, stigma) and this rule is generally followed here, though of course grass flowers have glumes, lemma, palea, stamens, stigma.
One important point to remember with grasses is that the flower spike can look very different according to how far along the process from flowering to setting seed that it is. Many species begin with a tight, rod-like cluster which opens out when in full flower and then closes back up again after pollination. Thus, it is important to look carefully at the parts of the florets (individual flowers) regardless of the shape of the overall flower spike, just to be sure. To get around this variability, botany books often write descriptions of grasses when they are said to be 'at anthesis'. This simply means at the point that the anthers open to release the pollen and this ensures that we are always looking at the flowers at the same point in their development. Grasses can still be identified outside of this point, but you need to understand that the overall spike might look different (the smaller flower parts will generally not change much, however). To simplify this a little, I have used the terms 'early flower spike/spikelets/florets' for spikes where the flowers have not yet reached anthesis; 'flowering spike' for plants at or around anthesis; 'late flower spike' for spikes where the flowers have passed anthesis and are progressing towards seed set. Where these terms are not used, you can assume that the flower spike doesn't change significantly in appearance over the course of the flowering period.
While this page contains the species that you are most likely to come across in most situations, it should be noted that most of them have look-alike, closely-related species. Therefore, it is recommended that you follow the link given for each species to the page where it will be compared in greater detail with possible confusion species, as a way of confirming your identification.
Common Bent Agrostis capillaris
A native perennial found in most grassy places but especially on acid soils, where it can form extensive stands. Widely used as a grass for fine lawns, due to its very narrow leaves. Flowers June to August. Plants 10-70cm in height and spreading by short rhizomes to form slightly tufted patches. Leaf blades 1-5mm wide, hairless, finely pointed at the tip. Leaf sheaths rounded, smooth. Leaf ligule membranous, long. Flower spike very narrow when young, open and spreading at anthesis and remaining open at fruiting. Spikelets tiny, 2-3.5mm, clustered towards the tips of very fine branchlets with a single floret in each spikelet. Lemmas not awned. Spikelets may be green (especially in shade) but are more often purplish. Compare with other bents.
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Common Sheep's Fescue Festuca ovina
A native perennial, Very common in a wide range of dry soils, both chalky and acidic and often forming extensive patches in suitable habitat. Flowers May to July. Plants to 50cm in height and forming dense tussocks. Leaf blades very narrow, 0.6-1.4mm wide, hairless, greyish-green to green, blunt at the tip and tightly inrolled. Leaf sheaths rounded, smooth, with rounded auricles and a very short ligule. Flower spike upright, spreading at anthesis, later closing up. Spikelets 5.3-7.2mm with 2-9 florets, upper glume 2.7-4.2mm, lemmas 3.3-4.9mm, with an awn 0.2-1.6mm long. Compare with other fescues.
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Squirreltail Fescue Vulpia bromoides
A native annual, widespread on dry, usually sandy, soils and often growing where there has been disturbance along track sides and near rabbit scratchings. Flowers May to July. Plants 5-60cm in height, stems clustered, or single in drier sites. Leaf blades 0.5-3mm wide, flat or inrolled, downy above, rough on the margins. Leaf sheaths rounded and smooth. Ligule membranous, up to 0.5mm in length. Flower spike with upright or slightly spreading branches, with many spikelets, or reduced to two or even just a single spikelet in dry ground. Spikelets 7-14mm long, with 5-10 florets. Lower glume 2.5-5mm long, half to three-quarters the length of the upper glume. Lemmas 5-7mm long with a long and slender awn to 13mm in length. As it's scientific name suggests, this little grass looks rather like a cross between a fescue and a brome. Compare with other fescues.
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Wavy Hair-grass Avenella flexuosa
A native perennial, confined to dry, acid heaths. Often abundant and can dominate large areas in ideal habitat, such as in the Suffolk Sandlings, Norfolk heaths and Breckland. Flowers June to July. Plants 20-90cm in height, forming tight tussocks. Leaves 0.3-0.8mm wide, narrow, inrolled. Leaf sheaths rounded. Ligule membranous, 0.5-3mm long, blunt at the tip. Flower spike flexuous, at first with branches held close together, but later open and broadly spreading, up to 15cm in length. Spikelets 4-6mm, each usually with 2 florets. Glumes very thin, almost membranous. Lemmas 3-5.5mm, membranous, awned. A very distinctive grass with the stems tinged pinkish-purple and the shiny spikelets waving in unison in the breeze.
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Early Hair-grass Aira praecox
A native annual, widespread on a wide range of dry and sandy or acidic soils; most common on acid heaths and dunes. Flowers April to June - one of the first grasses to flower in the spring. Plants 3-10cm in height, usually tussocky but sometimes solitary stems in difficult growing conditions. Leaves 0.3-0.5mm wide, narrow, inrolled and blunt at the tip. Leaf sheaths rounded. Ligule membranous, rounded at the tip. Flower spike compact, 0.5-5cm in length. Spikelets 2.5-4mm, each with 2 florets. Glumes relatively large, 2.5-4mm, enclosing the florets. Lemmas awned.
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Silver Hair-grass Aira caryophyllea
A native annual, widespread on a wide range of dry and sandy or acidic soils; most common on acid heaths and dunes but also along railways, dry tracks and paths. Flowers May to July. Plants 3-30cm in height, more typically at the lower end of the size range in dry habitats. Leaves 0.3-0.4mm wide, greyish-green, thread-like and inrolled and soony reddening in dry conditions. Leaf sheaths rounded. Ligule membranous, up to 5mm long, jagged at the tip. Flower spike compact at first, but fully open and wide-spreading at anthesis, 1-12cm in length. Spikelets 2.2-3.5mm, each with 2 florets. Glumes relatively large, 2.2-3.5mm, enclosing the florets. Lemmas awned from the back. A tiny grass that typically grows in small, scattered colonies, but can be easily overlooked due to its small size.
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Yorkshire-fog Holcus lanatus
A native perennial, common to abundant in many kinds of grassy places and often forming large stands on roadsides, banks and rough ground. On heathland, it often becomes established where the soil has been disturbed. Flowers May to September. Plants 20-100cm in height, variously as spaced stems or densely tussock-forming according to land use and management. Leaf blades 3-10mm wide, softly hairy or downy, flat and pointed. Leaf sheaths rounded, hairy. Ligule membranous, 1-4mm long. Flower spike very narrow when young and typically pinkish-purple in colour, spreading at anthesis and remaining open with age. Spikelets 4-6mm with usually 2 florets. Lemmas keeled, the lower unawned, uppers with a straight awn, to 2mm long and barely protruding beyond the glumes. Stem nodes conspicuously white-hairy and contrasting with the rest of the more or less hairless stem.
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Creeping Soft-grass Holcus mollis
A native perennial, common on a variety of soils but most often found on dry soils in shady places and often forming creeping patches in dry birch wood and under gorse and bracken, where other grasses are shaded out. Flowers June to August. Plants 20-50cm in height, often forming leafy colonies with few or no flowering spikes. Leaf blades 3-12mm wide, softly hairy or hairless, flat and pointed. Leaf sheaths rounded, hairy. Ligule membranous, 1-5mm long. Flower spike very narrow when young, spreading at anthesis and remaining open with age. Spikelets 4-7mm with usually 2 florets. Lemmas keeled, the lower unawned, uppers with a slightly bent awn, 3.5-5mm long and clearly protruding beyond the glumes. Stem nodes downy but not conspicuously so.
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Purple Moor-grass Molinia caerulea
A native perennial, favouring wet, peaty ground in fens, dune slacks and damp heaths. Flowers July to September. Plants 15-130cm in height, forming tight tussocks. Leaves 3-10mm wide, flat, rough at the margins and usually with a few long hairs towards the base; long-tapered to a fine point. Leaf sheaths rounded. Ligule a ring of stiff hairs. Flower spikes rather variable, but typically well-branched, narrow and wand-like, at first stiff and straight, later arching, up to 65cm in length. Spikelets 3-7.5mm, 1-4 flowered. Glumes shorter than the lemmas and typically purple-tinged. Lemmas 3-6mm, firm and smooth. A distinctive, late-flowering grass, forming dense tussocks of tough leaves topped with long, wand-like flower spikes, all of which persist well into winter as brightly straw-coloured clumps.
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Heath-grass Danthonia decumbens
A native perennial, occurring on a wide range of soils but most frequent on sandy heathland along open tracks and paths. Flowers June to August. Plants 10-60cm in height, forming small, low tussocks. Leaves 2-4mm wide, flat or inrolled, rich green and rather stiff. Leaf sheaths rounded, downy, with a tuft of stiffer hairs at the top. Ligule a ring of short, dense hairs. Flower spikes rather variable, but typically narrow, 2-10cm in length with 3-12 spikelets. Spikelets 6-12mm, 2-6 flowered. Glumes rounded at the base, becoming keeled towards the tip and almost as long as the spikelet. Lemmas 5-7mm, firm and smooth, with minutely three-toothed tips. Typically a tiny and easily overlooked species with a rather sedge-like look about it.
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Mat-grass Nardus stricta
A native perennial, which can be dominant and abundant in upland grassland in northern and western Britain but is rare and declining in East Anglia. Found in small quantity on a scattering of dry, sandy and acidic heaths, dunes and grasslands. Flowers June to August. Plants 10-40cm in height, forming small, wiry tussocks. Leaves 0.5mm wide, tough, sharply-pointed and inrolled. Leaf sheaths rounded, smooth. Ligule membranous, 0.5-2mm long. Flower spikes narrow, stiff and upright, 3-8cm in length, purple-tinged and with all the spikelets on one side. Spikelets 5-9mm, 1-flowered and inset into the axis of the spike. Glumes tiny, with the upper often absent altogether. Lemmas 6-9mm, two- to three-keeled and tapered to a fine awn at the tip. A tiny and easily overlooked species in East Anglia.
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