16-May London’s Secret Grasses

What we see as a flower head in a grass is called a panicle and what might pass as flowers are called spikelets. Inside the spikelets, which we can see with the naked eye, are the true flowers which are called florets. There can be just one or several florets in a spikelet and a lens is really needed to examine them any further. Any bristle or hair-like structure projecting out of a floret or spikelet is called an awn and their presence or absence is often important in securing a field identification.

The only grass that you may have noticed a lot as it is everywhere and been in flower since January is the Annual meadow grass Poa annua. Its panicle is triangular in outline with many small greenish, occasionally violet-tinged, spikelets set upon paired branches. Each spikelet has between two and five tiny florets inside it and no awns projecting from any of them. Another meadow grass comes into flower this month and is generally very similar-looking but usually much larger. This is the Smooth meadow grass Poa pratensis. Its panicle is similarly triangular-shaped but its branches differ coming off the main stem in whorls rather than paired branches. It also has no awns projecting from its florets. It is one of our greenest grasses greatly adding to the beauty of meadows as well as lawns and sports pitches.

Two other very early-flowering grasses that tend to get noticed especially on walls or sandy ground are the Early hair grass Aira praecox and the Silver hair grass Aira caryophyllea. The most noticeable thing about Early-flowering hair grass is its diminutive size. It rarely exceeds 10 cms in height. You usually just notice a neat tuft of bristle-like leaves with several flowering stems. The panicles are a mere two to three centimetres in height and like many hair grasses have a silvery sheen. Its companion this month is quite different although it grows in the same places. The Silver hair grass has a panicle which is much more open with hair-like branching and tiny well spaced silvery spikelets. This makes for an exceptionally delicate-looking grass that is so attractive it used to be planted ornamentally in rockeries.

Two more quite different grasses are now starting to be seen a lot on waste ground, roadsides and at the edges of sports pitches. These are both rye grasses i.e. Perennial rye grass Lolium perenne and its close relation Italian rye grass L. multiflorum. Rye grasses typically have no branching just a simple spike with two rows of spikelets alternately arranged looking just like two rows. At this time of year there is little you could confuse them with and they can easily be told apart with Perennial rye grass having no awns projecting from its spikelets and Italian rye grass having several. The former species is thought to be the first grass ever cultivated by man and has been sown here in England to create pasture since the seventeenth century.

A group of very familiar-looking grasses are the foxtails Alopecurus spp. They have a flower head of compressed spikelets which is pleasant to touch and not unlike a miniature foxtail in appearance. By way of introduction we have two that come into flower this month i.e. the Meadow foxtail Alopecurus pratensis and the Slender foxtail or Black grass A. myosuroides. They are both tall grasses which can be told apart easily. Meadow foxtail has a flower head or panicle which is blunt at both ends and the Slender foxtail a panicle which is tapered at both ends. If this is not enough, Meadow foxtail is typically found in damp grassland and the Slender foxtail in much drier situations such as waste ground, roadsides and as an arable weed

Yet another main group of grasses are the fescues Festuca spp. Fortunately these are represented by just two species this month i.e. Sheep’s fescue Festuca ovina and Red fescue F. rubra. Fescues generally tend to be large, with loose panicles and branches that arise either singly or in pairs off the main stem but never in whorls. They generally have three or more florets in each of their spikelets giving them a slightly fatter appearance. Sheep’s fescue is a grass associated with poor soils where it can form a turf which provides valuable grazing for sheep. This tough grass forms tufts of bristle-like leaves which are often curved and has oblong rather than oval spikelets. In comparison the only other fescue you are likely to see this month is quite different. Red fescue isn’t usually red and tends to look like a taller version of Sheep’s fescue with a panicle which is more compressed at its tip, sometimes almost coming to a point. Although often the most common grass in a meadow, in its different forms it is also a grass of fine lawns and sports fields. One other fescue which isn’t really a fescue is the Squirrel-tail fescue Vulpia bromoides. The squirrel-tail refers to the many long awns that give the grass a much hairier look than other fescues. Its panicle tends to be much more compact than the other two fescues and it is often found in sandy areas and on railway embankments.

Bromes are yet another group of very diverse grasses. This month the first to be seen will be the Barren brome Bromus sterilis which has many typical features of the group such as a loosely branched panicle with long stalked spikelets that tend to hang down. Other features of Barren brome are that it is often purple and its panicles droop so much they often bend and sway in the wind. It is also unusual just having one floret in each of its panicles making them look very thin as if they were barren. This is the grass that is ubiquitous in London on waste ground and roadsides for much of the rest of the year.

Millets (Milium spp.) tend to be hairless grasses with grey-green leaves and panicles of small well-separated spikelets with no awns. There is just one you might find this month but it is likely to be the most impressive grass you see the whole month i.e. Wood millet Milium effusum. It grows sometimes in numbers in old woodland particularly in beechwoods. Here it can reach 180 cms in height with a typical wide open panicle decorated with tiny awnless spikelets at the end of long branches. Its size and elegance explains why gardeners plant it as an ornamental in the shadier parts of their gardens. Sweet grasses (Glyceria spp.) are another type of grass, this time associated with aquatic habitats. There are two this month that are instantly recognisable due to their floating ribbon-like leaves we see on the surface of lakes and slow-moving rivers.

These are Floating Sweet grass Glyceria fluitans and Plicate Sweetgrass G. plicata. They can be told apart by looking at their leaves which in Floating Sweet grass suddenly narrow towards their tips whereas in Plicate Sweetgrass are much more tapered. Also the panicles of the former are far less branched than those of the latter. The seeds of these grasses are both edible and sweet sufficiently so that cattle are known to wade out into lakes to eat them.

Lastly there are two more very noticeable grasses that are likely to be seen a lot. The first is Cocksfoot Dactylis glomerata which seems to be almost everywhere, not just now but for most of the rest of the year. It is a distinctive tall, coarse grass with densely packed spikelets in rounded clusters that are often tinged with lilac. Its long flat leaves also have prominent keels. At one time it was an important grass of permanent pasture and its hay provided food for horses.

The second is Sweet Vernal grass Anthoxanthum oderatum. In mid April on the dry meadows and commons it prefers it is likely to be the only flowering grass you will see. Its densely packed terminal spikes that start off greenish yellow and then turn to a golden yellow usually allows for easy identification. What sets this grass apart are glands in its spikelets that emit the famous soothing scent coumarin which we associate with hayfields in high summer. This scent also gets stronger when the grass is either dried or crushed as you sometimes notice when lawns are cut. Although of little use as cattle fodder it is included in most seed mixtures purely because of its scent.