Things to look for when identifying grasses

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Explanatory Notes

1. Habitat
Where the grass is found.

Different grasses prefer different types of habitat. For example, some species thrive in shady woodland conditions, whereas others need more light and prefer open ground. Habitat species lists for grasses can help to narrow down the number of possible species.

2. Habit
Is it perennial or annual?

Is it tufted or creeping?

Is it rhizomatous or stoloniferous?

In annual grasses (which grow, flower and die within the same year) all or most of the shoots will flower. Perennial grasses, in contrast, may live for many years. In these grasses, some of the shoots will flower and some will not.

Some grasses grow in localized clumps (tufted), while others spread out, often over large areas (creeping). They do this via stems which either creep along the top of the ground (stoloniferous) or underneath it (rhizomatous).

Stolons tend to have greenish/purplish stems, while rhizomes are whitish or brownish. Stolons also have complete green leaves at the nodes, whereas rhizomes have only white/brown scale-like leaves at these points.

3. Leaf sheaths
Are they hairy or glabrous?

Rounded or keeled?

Closed or open?

The leaf sheaths are the part of the leaf which encircles the grass stem, before it opens out into the leaf blade. Glabrous means it has no hairs. A hand lens may be needed to check this feature.

Some grass stems feel rounded when you run your hand up the encircling leaf sheaths, while other species may have a distinct ridge or keel, like that of a boat, on one side.

The leaf sheath may either encircle the stem with the edges joined to make a complete tube (closed), or one margin of the sheath may overlap the other (open).

4. Leaf blades
Are they hairy or glabrous?

Flat or rolled?

Pointed or hooded tipped?

Rolled or folded when new?

The leaf blades, where they leave the stem, open out into either a flat blade, or a more tubular leaf blade with inrolled edges.

The leaf tips may be pointed or may have the sides joined together like the bow of a boat (i.e. hooded - left).

New young leaves growing up inside the sheathing bases of older leaves, are either rolled longitudinally around the stem with one margin innermost, or alternatively folded in half longitudinally along the midrib.

5. Ligules
Are they membranous or a fringe of hairs?

Are the ligules short or long?

(Diagram here)

At the junction of leaf blade and leaf sheath, there is a small membranous extension called a ligule. These vary from 1-2mm, to several millimeters in length.

(Click on the images to go to a larger picture.)
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Ring of hairs at leaf blade/sheath junction

Membranous ligule (in the centre at right).

Sometimes the ligule consists of a ring of hairs (left).

6. The Inflorescence

Is it a panicle, raceme or spike?

Left: 3 spikes of Rye Grass.

Right: a panicle

More explanation here

7. Spikelets
Are they one, two or many flowered?

(Diagram here)

This spikelet has 8 florets. The actual number of florets in each spikelet may vary slightly even within the same inflorescence.

(annotated image here)

8. Glumes
Are they hairy or awned?

How many veins do they have?

What size are the veins?

The glumes are the outermost pair of scales enclosing the spikelet at the base. They protect the flowers inside before opening.

The glumes may be hairy and/or may have a bristle-like extension called an awn.

Examination with a hand lens will reveal the veins on the glumes, as well as awns, if they are present. If the awns are long, they may easily be seen with the naked eye.

9. Lemmas
As for glumes.

(Diagram here)

Each floret inside a spikelet is protected by its own individual pair of covering scales, one called the palea and the other the lemma. The lemma is the outer scale of the pair. These have diagnostic features similar to those described for glumes above.

10. Anthers
How long are they?

Anthers hanging out of the florets in an inflorescence.

The length of the anthers (the purple sacs in the picture at left) can be diagnostic.

(A hand lens or microscope is needed to check this feature.)