Grasses: Urban Sites - Walls, Pavements & Paths
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?
Grasses can be rapid colonisers of open ground and this page includes the most frequent species that can be found growing in the hard landscaping of urban areas. A wide range of species can, on odd occasions, be found growing from cracks in pavements and walls, but most grasses found in such areas are likely to be found on this page. Any paved areas in towns or cities are likely to have cracks that provide a place for these species to grow, while the tops of old walls, especially if the tops are flat or have their coping stones missing, commonly attract a number of grass species.
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 (i.e. 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. Note that plants growing from cracks or from walls can be rather impoverished due to the difficult growing conditions, so they will often be rather small and with rather fewer flowers than is typical for the species.
Wall Barley Hordeum murinum
A native annual. Common to abundant in rough, disturbed or neglected ground and especially common in urban areas on walls, cracks in pavements etc. Flowers May to August. Plants 6-60cm in height, often forming linear colonies along track sides and the foot of walls. Leaf blades 2-8mm wide, softly downy or smooth, rather limp and typically arching over. Leaf sheaths rounded, the lower ones hairy, the uppers hairless. Ligule membranous, very short and largely hidden by the winged auricles that wrap around the stem. Flower spike upright or slightly nodding, 4-12cm long. Spikelets each with a single floret, attached to each other in groups of three, the middle floret bisexual, the outer two male or sterile. Lemmas long and narrow, with a long awn 10-50mm in length. Compare with other barleys.
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Annual Meadow-grass Poa annua
A native annual or short-lived perennial found in all types of open ground, bare patches in lawns, gravel drives, cracks in walls and pavements etc. Flowers more or less throughout the year, but especially from late November to June. Leaves hairless, pointed at the tip or slightly rounded and hooded, 1-5mm wide. Flower spike open and spreading at anthesis and remaining open at fruiting. Spikelets densely packed with 3-10 florets. Plants in dry places can be very small and compact, but more open and spreading in shady or wetter places. Compare with other meadow-grasses.
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Smooth Meadow-grass Poa pratensis
A native perennial found in many types of grassy places such as lawns, meadows and roadsides, as well as cracks in walls and pavements etc., but typically avoiding wetter places. Flowers May to July. Plants 10-80cm in height according to habitat (shorter in dry, open places, taller when among other plants or in shade) and spreading to form extensive patches. Leaf blades and sheaths hairless, pointed at the tip or slightly rounded and hooded, 2-5mm wide. Leaf ligule mebranous, short. Flower spike open and spreading at anthesis and remaining open at fruiting, with 3-5 branches at the lowest node. Spikelets densely packed with 2-5 florets. Note that this is the commonest of a cluster of rather similar species and subspecies found in East Anglia. Compare with other meadow-grasses.
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Narrow-leaved Meadow-grass Poa angustifolia
A native perennial found in grassy places on dry soils such as heaths, commons and roadsides, as well as cracks in walls and pavements etc. Flowers April to July. Plants 20-70cm in height according to habitat. Leaf blades 1.5-2mm wide, rather variable but generally noticeably fine and narrow. Leaf ligule membranous, short. Flower spike open and spreading at anthesis and remaining open at fruiting, branches fine, mostly in clusters of 3-5. Spikelets relatively small, 2.5-5mm, densely packed with 2-5 florets. Told from similar meadow-grasses by the long, narrow and rather stiff leaves that can resemble those of Red fescue. Compare with other meadow-grasses.
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Spreading Meadow-grass Poa humilis
A native perennial found in a wide range of grassy places, as well as cracks in walls and pavements etc. Flowers June to July. Plants 3.5-25cm in height according to habitat. Leaf blades 1.5-4mm wide, rather variable but often slightly bluish-tinted and relatively short. Leaf ligule membranous, short, often accompanied by stiff hairs around the base of the leaf blade. Flower spike open and spreading at anthesis and remaining open at fruiting, branches mostly in clusters of 2-3 (including at the lowest node). Spikelets 4-7mm, densely packed with 2-4 florets. A rather small meadow-grass with often solitary and widely spaced flower spikes. Compare with other meadow-grasses.
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Flattened Meadow-grass Poa compressa
A native perennial which favours dry ground and takes readily to growing from cracks in walls and pavements etc. Flowers June to August. Plants 10-60cm in height with stems distinctly flattened in one plain. Leaf blades 1-4mm wide, bluish- or greyish-green with keeled sheaths. Leaf ligule membranous, rounded, 0.5-3mm long. Flower spike rather variable but typically with rather short lower branches, giving it a rather cylindrical outline. Spikelets 3-8mm, with 3-10 florets. The stiff, flattened stems and rather narrow flower spikes are rather distinctive. Compare with other meadow-grasses.
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Water Bent Polypogon viridis
An introduced annual or short-lived perennial, probably being spread as a weed of the nursery industry and once a rare casual, but now increasingly common in urban situations, growing from cracks in paving and walls and occasionally in flowerbeds and gravel paths. Flowers June to August. Plants 10-60cm in height with perennial plants forming creeping stolons and tufted patches. Leaf blades 2-10mm wide, hairless but a little rough to the touch, pointed at the tip. Leaf sheaths rounded, smooth. Leaf ligule membranous, rounded, 1.5-6mm long. Flower spike narrow when young, open and spreading at anthesis and remaining open at fruiting. Spikelets tiny, 1.7-2.2mm, very numerous, not clustered towards the tips of the branchlets with a single floret in each spikelet. Lemmas not awned. Rather distinctive once known, with relatively broad leaves held out, flag-like from the flower spikes and with a dense mass of florets.
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Common Bent Agrostis capillaris
A native perennial found in most grassy places but especially on acid soils. Widely used as a grass for fine lawns and often spreading into nearby paving. 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 mebranous, 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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Creeping Bent Agrostis stolonifera
A native perennial, abundant in grassy places and readily spreading into nearby tracks and paving. Flowers July to August. Plants 10-80cm in height and spreading by long, creeping stolons to form large, spreading patches. Leaf blades 0.5-5mm wide, hairless, finely pointed at the tip, rolled when young but eventually flat. Leaf sheaths rounded, smooth. Leaf ligule mebranous, medium to long. Flower spike very narrow when young, open and spreading at anthesis then closing again at fruiting. Spikelets tiny, 2-3mm, clustered towards the tips of very fine branchlets with a single floret in each spikelet. Lemmas not awned. Compare with other bents.
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Red Fescue Festuca rubra
A native perennial, abundant in all kinds of grassy places and commonly cropping up on walls and in tracks and paving. Flowers June to August. Very variable in appearance with several subspecies recognised, especially in coastal habitats. Plants 20-100cm in height and variably spreading or clump forming. Leaf blades often very fine, 1-5mm or more wide according to subspecies, hairless, finely pointed at the tip, rolled or flat. Leaf sheaths rounded, smooth, fused together more or less to the top and hiding the minuscule ligule. Flower spike spreading at anthesis, often slightly drooping towards the tip when young. Spikelets 5-14mm with 3-12 florets. Lemmas shortly awned. Compare with other fescues.
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Rat's-tail Fescue Vulpia myuros
A native annual, widespread in many kinds of open and disturbed habitats, especially on dry or sandy soils and as a weed on walls and pavements. Flowers May to July. Plants 10-70cm in height, larger plants tussocky with many stems but single- or few-stemmed in drier sites. Leaf blades 0.5-3mm wide, flat or inrolled, downy above, smooth beneath. Leaf sheaths rounded and smooth. Ligule membranous, short to medium. Flower spike narrow and gracefully upright. Spikelets 7-10mm long, with 3-7 florets, loosely spaced in the spike. Lemmas 5-7mm long with a long and slender awn to 15mm in length. Compare with other fescues.
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Squirreltail Fescue Vulpia bromoides
A native annual, widespread on dry, usually sandy, soils and as a weed in urban areas. 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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Barren Brome Anisantha sterilis
A native annual, or overwintering as a biennial. Common to abundant in rough, disturbed or neglected ground, especially along roadsides, tracks and in urban habitats. Flowers May to July. Plants 15-100cm in height, very variable according to growing conditions. Leaf blades 2-7mm wide, coarse and shortly hairy, the blades typically spirally twisted. Leaf sheaths rounded and hairy. Ligule membranous, long and ragged-tipped. Flower spike consisting of long, slender branches, typically arching gracefully over to one side. Spikelets 40-60mm (including the very long awns) with 4-10 florets, the spikelets carried at the ends of the long branches. Lemmas strongly overlapping at first, later more open, with a long awn 15-30mm in length. Compare with other bromes.
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Common Soft-brome Bromus hordeaceus
A native annual, or overwintering as a biennial. Common to abundant in rough, disturbed or neglected ground as well as in open swards in meadows. Flowers May to July. Plants 15-80cm in height, extremely variable according to growing conditions. Leaf blades 2-7mm wide, softly downy. Leaf sheaths rounded and hairy (often hairless on the uppermost sheaths). Ligule membranous, medium length and ragged-tipped. Flower spike upright at first, becoming more open at anthesis, then the branches closing together again later. Spikelets 12-22mm with 6-12 florets (really small plants may have just a single spikelet). Lemmas strongly overlapping, downy, with a short awn 5-10mm in length. The commonest form in a complex group of rather similar species and subspecies. Compare with other bromes.
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Perennial Rye-grass Lolium perenne
A native perennial, abundant in most grassy habitats and commonly forming tight mounds in pavement cracks and gravel paths. Flowers May to August. Plants 30-80cm in height, variably tussocky or more open and with non-flowering shoots (tillers) at flowering and fruiting time as well as creeping rhizomes. Leaf blades 2-6mm wide, hairless, slightly ridged on the upper side and distinctly glossy on the underside. Leaf sheaths rounded and hairless. Ligule membranous, short. Flower spike long, narrow and wiry. Spikelets 7-20mm with 4-14 florets, alternating from one side to the other along a sinuous central stem, with the flat face of the spikelets at 90 degrees to the central stem. Lemmas blunt or pointed at the tip, but without awns. Compare with other rye-grasses.
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Common Couch Elymus repens
A native perennial, common to abundant in a wide range of disturbed and open ground, roadsides and grassy places and readily spreading onto nearby tracks and paving. Flowers May to August. Plants 30-120cm in height, variably tussocky or more often forming extensive patches from far-creeping rhizomes. Plants may be green or strongly glaucous (blue-grey). Leaf blades 1.5-10mm wide, hairless, slightly ridged and variably downy on the upper side and rough on the underside, the ridges having rounded (not flat) tops. Leaf sheaths rounded and hairless on the upper leaves, downy on the lower leaves, with the sheaths of the lower leaves not having a row of minute hairs along their exposed margin. Ligule membranous, very short. Flower spike upright or drooping to one side. Spikelets 10-20mm with 3-8 florets, alternating from one side to the other along a sinuous central stem, with the flat face of the spikelets facing the central stem, like clapping hands. Lemmas blunt or pointed at the tip, with or without an awn to 15mm in length. Largely replaced in coastal habitats by Sea Couch (Elymus athericus). Compare with other couches.
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Rigid Fern-grass Catapodium rigidum
A native annual, widespread in dry ground near the sea and in sandy places and common on walls in urban environments. Flowers May to July. Plants 2-30cm in height, typically forming tight tussocks or solitary shoots in small colonies. Plants green, or becoming reddish in very dry and sunny places. Leaf blades 0.5-3.5mm wide, hairless, minutely rough on the veins. Leaf sheaths rounded and smooth. Ligule membranous, very short, 1-3mm long. Flower spike stiffly upright, 1-8cm long. Spikelets 4.5-7mm with 3-10 florets, tightly clustered along side branches of the flower spike. Lemmas narrowly obtuse at apex overlapping at first, later becoming more open.
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