Common Grass species identification: Some easy shortcuts

As you may have noticed, I’m rather obsessed with grasses, and have blogged on them often.  From an introduction, to learning about them, to celebrating their beauty , discussing the ecological significance of Maram grass (guest blog), and more recently, to telling them from Rushes and sedges

And, of course, I do botanical illustrations of them rather frequently.

Selection of grasses

I went on an FSC course recently, this time on identifying grasses (other grass courses by FSC are available here).  And one of the things I learned was some really quick tips to help identify some fairly common grasses.  So I’m going to share them.

Common grasses: Cocksfoot

I think Cocksfoot Dactylis glomerata is one of the easiest grasses to learn.  It forms thick clumps, and is rather blueish.  Leaves are folded as they grow.  They’re sometimes crinkled, as if the grass is being pushed up.  But the give away is the way the flowering heads branch.  They almost always have two lower branches which come out at wide angles from the stem.  this explains the name as people reckon the branches look like the divergent toes of a cockerel.  It grows from 15 – 140cm.  The ligule is quite long, white, and looks “torn” or ripped.

Cocksfoot Dactylis glomerata

The lower stem is often pale or even white.

Detail of Cocksfoot ligule

My two illustrations of separate plants show this diagnostic lower branch pattern pretty clearly.  The flowering spikelets are often tinged pink or purple, but be aware that this is true for quite a few grass species.

Common grasses: Rye grass

Rye grass Lolium perenne is ubiquitous.  It’s planted for grazing and also makes up the bulk of grass seed for lawns.  It’s incredibly tough, and will often be the grass still standing after being mown.  You often see residual flowering spikes all through the winter.  If unmown, it will grow to 10 – 90cm.

Rye grass Lolium perenne

Rye grass is really shiny green, especially when young.  Unlike most grasses, its flowers cling very closely to the stem.  They don’t branch out or droop.  The only other species that bears its flowers in a similar pattern is the Italian Rye grass.

Italian Rye grass Lolium multiflorum

The main difference between these two is that the Italian rye has spines or “awns” on its spikelets.  But you can see how similar the form of the flowering spike is.

Common grasses: Sweet Vernal Grass

Sweet vernal grass Anthoxum odoratum is another common grass.   It’s one of the first grasses to flower.  This species can grow up to 80cm high.  As the name suggests, it smells rather strongly of hay.  This comes from high levels of cumarin which is what gives hay its distinctive sweet smell.  Crush a blade of Sweet vernal grass and, in theory at least, you should be able to smell it.

Sweet Vernal grass Anthoxanum odoratum

It also has a “beard” of hairs around it’s ligule.  The only other UK grass to have a similar beard is the Heath grass Danthonia decumbens which only grows in arid places.

Detail of ligule of the Sweet vernal grass

Common grasses: Common Reed

Common reed Phragmites australis grows in rivers, canals, and ponds, and damp places.  It has broad blue-ish leaves.  It is a really big plant, growing to 2 – 3 m tall.

Common reed Phragmites australis

Reed flowers are quite easy to see too.  The outer layers are often flushed maroon which gives the flowering head a purplish look, and the spikelets have long spines or awns.

The big give-away with the reed is its ligule.  Unlike most grasses, it doesn’t have a membraneous one.  Its ligule is a simple circle of long hairs.  It’s the only UK grass that has this feature.  Coupled with it’s love for moist habitats, you can recognize the Common reed with no trouble.

Detail of an individual spikelet and the ligule of hairs of the Common Reed

Common grasses: Yorkshire fog

Yorkshire fog Holcus lannatus is one of my favourite grasses.  It feels different to almost all the other grasses (except the closely related Creeping soft grass Holcus mollis which tends to grow in woodlands not meadows), as if it’s made of incredibly fine velvet.  It grows from 20 – 100cm tall.

Yorkshire fog Holcus lanatus

The spikelets are often flushed a beautiful pink.  It’s worth noting that the flowering spike hides inside the sheath of a leaf blade before flowering, so you often see if very compressed.  Once in full flower, it has a wide spreading flowering head.

Yorkshire fog Holcus lanatus

But if this velvety texture doesn’t convince you, there’s another way to check you are looking at Yorkshire fog.  Have a rummage right down at the base of the plant, and look closely at the stems. If you see pink stripes, like old fashioned pyjamas, then you’ve got Yorkshire fog.  In fact, the whole plant is flushed pink, but again, that alone isn’t a species diagnostic.  The pyjama stripes are.

Pink “pyjama stripes” at base of Yorkshire fog

Common grasses: False Oat grass

False Oat grass Arrhenatherum elatius is everywhere.  You’re very likely to find it on road verges and in recently disturbed places, or unmanaged land.  It’s known as a ruderal species.  Although the flowering head is branched, the branches come close together once fertilized.  This makes the flowering heads look like graceful silvery arches. The leaves are flat and a dull green.

False Oat grass Arrhenatherum elatius

 The spikelets have really long awns, as long as the entire spikelet.  The long awns give the grass the effect of being very silvery as it catches the light. Each spikelet only holds two florets, one of which has the reproductive flowering parts.  Here’s a close up of the flower, showing the distinctive long awn:

Flower and lemma of the False Oat grass Arrhenatherum elatius

But there’s one more trick to identifying False oat grass.  Look at the roots.  The base of this grass has yellow-orange roots.  these are really distinctive, and may also be swollen into round bulb-like structures. For me, the yellow roots are the final piece of jigsaw that helps me i.d. this one right every time.

Yellow roots of the False Oat grass

Common grasses: Spotting your Meadow grasses

This is a bit of a cheat as it won’t take you to an actual specific species.  But many of our UK species are Poa, or members of the Meadow grass family.  So how can you tell if a grass is a Poa?  It’s mostly down to the distribution of the branches on the flowering spike.  If they grow in whorls, and the inflorescence is like a christmas tree in shape, then you’re likely to have a Meadow grass.

Rough meadow grass Poa trivialis

One other group of UK grasses are also whorled in growth, the Bents.  However, Bent grasses (like Common or Creeping bent Agrostis capillaris) flower later in the year.  They also have tiny flowers, much smaller than the Meadow grasses.  Also, Bent grasses only have one floret per spikelet.  Poa have many more.  The meadow grass above, Rough meadow grass Poa trivialis, can be identified by rubbing the stem on your upper lip.  if it’s rough, then it’s likely to be P. trivialis rather than any other meadow grass.

Meadow grasses are another of the species who have really obvious flattened and keeled leaves (like the Cocksfoot).  These blades are said to be “boat shaped”, with a distinct prow.  They look as if they’ve been folded in half.

Conclusion

So there you are.  A whistle stop tour of some of our commonest grasses, and how to identify them.  There are others that are crazily easy – the Bearded couch Elytrigia repens has extremely purple nodes (at least in woodland habitats).  It has distinct claws where the leaf blade meets the stem, and very little in the way of ligules.  These claws (“auricles”) are also flushed a vibrant purple. Look out for it in woodlands.

The Quaking grasses are easy too, mainly because they look so dissimilar to everything else.  They tremble in the breeze, grow in dry heathland, and are one of our prettiest grasses.

Quaking grass Briza media

And the Crested Dog’s hair Cynosurus cristatus is another one to keep an eye out for.  At a push it might be confused with Rye grass, but it’s distinctive zig-zag inflorescence feels very different.

Crested Dog’s hair grass Cynosurus cristatus

I hope I’ve managed to share some of my love of these diverse and glorious plants.  Not only are they fabulous and frequently overlooked, but they’re also wonderful to illustrate!  Now you;re able to identify a few species, give it a go.  You may well find yourself entirely bewitched by grasses, like I am.