Saturday, September 26, 2009

Couch Grass (Elymus elegans) and Perennial Ryegrass (Lobium perenne)

I am an amateur naturalist trying to learn something about everything living in my garden.

Success in discovering the identity of some plant or animal is all about the careful and methodical observation of details. I've written this before, and had I only paid attention to my own dictum, I might avoided wasting half a morning recently getting thoroughly confused over the species of some grass growing in a corner of my garden!

Intrigued by a comment in a booklet Practical Microscopy (Eric Marson, Northern Biological Supplies) - a superb guide I cannot recommend too highly to any amateur interested in preparing their own high quality microscope slides - I had set out to examine some blades of grass under my microscope.

Venturing into my garden I came across the grass in photo 1. The long, seed bearing structure is technically termed a 'spike'. I picked a little and came back inside but before putting it under the microscope I decided to try identifying the species using my copy of Grasses (Fitter publ. Collins). Having only a few inches of specimen, it wasn't long before I was stuck however. I went back outside therefore, found my clump of grass and picked a little more. Embassingly foolish as it seems now, this went on for nearly an hour, with me traipsing back and forth, collecting a little more grass each time and returning inside only to find myself more confused than ever.

Finally, in exas- peration, I threw away my growing collection of tattered grass cuttings and started a fresh, and this time, methodical study. The result was the arrangement in photo 2 and the belated realisation I'd been collecting bits of two different grasses!

The two in question are Couch grass (Elymus repens) (photo 2, upper) and Perennial Ryegress (Lolium perenne). Laid out neatly in photo 2 the differences are obvious. I can say that it underlines the lesson that one cannot trust that causal glance at that seemingly undifferentiated clump of 'spike bearing' grass swaying in the breeze!

One difference between the two grasses in photo 2 is leaf size. In fact however, this is not an overly useful guide to species identification, as the size of the leaf baldes can vary with their position on the 'stalk' (culm) and other factors (soil quality etc.). Instead, amongst the most useful guides to a grass's species is the shape and size of the ligule, a small vestigial leaf-like structure the nestles between the culm and a leaf. Photo 3 shows the ligule of Perennial Ryegrass. By contrast, Couch grass lacks a ligule (though just to confuse the unwary, the leaves wrap around the culm via two little sheath-like flaps know as auricles - see photo 4).

Returning to the spikes of my two grasses, photo 5 shows a closeup of both. These bear the grasses' minute flowers (the source of all that hayfever-inducing pollen in summer). As I learnt in my previous study of the Cultivated Oat (Avena sativa), the structure of grass flowers comes with a lot of botanical jargon. I'll not repeat it here, but for completeness I've labelled up photo's 6 and 7.

And what of that micro scope image I originally set out to acquire? Well, as everyone knows you can get a painful cut from the edge of a blade of grass. Putting one under the micro scope (photo 8) shows just why: a margin decorated with a row of tiny saw-toothed daggers. Another of nature's tiny miracles.


Anonymous said...

I like your detailed photos of the grasses. It's good to see the named parts of the florets. The botanists, annoyingly, keep changing the names and the couch grass is now Elytrigia repens.


lodule said...

Unlike Anonymous, my reference calls Couch grass Agropyron repens.
J.C.E. Hubbard 1984