Grass, Rush or Sedge?

"Sedges have edges, rushes are round; Grasses have nodes right down to the ground". There are many variations of this little rhyme, which demonstrates that the problem of telling a grass from a rush from a sedge is commonplace and many attempts have been made to provide a short and easy way to tell them apart - but none of the variations of this rhyme truly work in all cases. Such is the variety of these groups of plants (especially the grasses), that coming up with a 'quick fix' is not easy, but this page will hopefully lead you in the right direction.

Here, the basic differences between these groups of plants are highlighted but, as is so often the case in nature, there always seems to be the odd one that doesn't play by the rules! Two very important things to remember are that the sedge family contains a wealth of species other than true sedges (in the genus Carex) and these have features that are often rather more like those of rushes than sedges; these plants will fall in the sedge allies group. Secondly, it should be remembered that sedges and rushes - once learned - tend to fall rather neatly into their groups, but that grasses are extremely diverse and summing them all up in a few short sentences is hardly possible. Thus, it is often best to rule out sedges and rushes first and move on to the larger grass group if those have been successfully ruled out. It is worth bearing in mind that if your plant is at all hairy, it's very likely to be a grass as very few of the rushes and sedges groups are hairy.

It is often not realised that all of these groups are flowering plants. It is common to hear people talk about 'flowers and grasses', as though grasses do not have flowers; but this is simply because of the false belief that flowers are always bright, colourful and showy. Grasses, rushes and sedges clearly have flowers, but they tend to be green, brown or straw-coloured and don't obviously contrast greatly from their vegetative parts.

To make the page sizes more manageable, grasses are covered on another page. You can click here to go straight to grasses, or continue from the link at the foot of this page.

Rushes & Wood-rushes

The family Juncaceae consists of the true rushes in the genus Juncus and the wood-rushes in the genus Luzula. The Juncus species typically have rounded stems in cross-section and often have no leaves. Those species with leaves may have them rounded like the stems (sometimes slightly compressed in one plane) or flattened like grass leaves. The stems and leaves may have cross-struts within them, which can be felt if the stem or leaf is squeezed between the thumb and forefinger and run along their length.

The flowers may appear in a densely compact cluster, or may be in an open, spreading head; they are carried at the tips of the stems, but sometimes a bract continues beyond the flower cluster, making it appear that the flowers are on the side (not at the tip) of the stem. The flowers have three sepals and three petals which are all similar (and thus referred to as tepals) and may open out in star-shaped arrangement, or may form a more closed, cup or vase shape. There are six stamens and three stigmas. The fruits are typically oval or rounded, brown nutlets.

Rushes - growth style


Tight clumps of upright stems	spreading patches of stems	Low plants with branching stems

Rushes - stems & leaves


Shiny and very smooth stems	Stems ridged lengthwise	Stems sometimes with cross-struts inside	If present, leaves clasp the stem

Rushes - flowerheads


Open, lightly branched flowerhead	Open, lightly branched flowerhead	Open, many-branched flowerhead	Tight, many-branched flowerhead

Rushes - flowers


Open stars with six, pale tepals	Open stars with six, brown tepals	Flowers with six stamens and three stigmas	Flowers with upright tepals, forming a vase-shaped flower

Rushes - fruits


Fruiting head	Fruits in an open cluster	Fruits in a compact cluster	Fruits in a compact cluster

Wood-rushes - growth style


Tight clumps or patches of curved leaves	spreading patches of short stems	Flowerheads emerge from a rosette of hairy leaves

Wood-rushes - leaves


New leaves emerge from a thick wad of white hairs	White hairs on leaf margins	White hairs on leaf margins

Wood-rushes - flowerheads


Flowers densely packed at first	Flowerheads become more open with age	Some species have large, spreading flowerheads

Wood-rushes - flowers


Flower cluster with pollen not yet dispersed	Flowers with stigmas extended before tepals open	Mature flower with pollen gone and tepals fully open

Wood-rushes - fruits


Flowerhead with young fruits	Fruiting head	Fruiting head	Close-up of nutlets

Sedges

The family Cyperaceae is a rather large family of grass-like plants, most of which (in the UK at least) are in the genus Carex and these can be thought of as the 'true sedges'. Other members of the family are treated below as the 'sedge allies' - species that are in the same family as the Carex species, but which differ in some key ways in their appearance. True sedges typically have stems that are triangular in cross-section, which can be checked by twirling the stem between the thumb and forefinger and feeling the bumpy corners. The three corners of the stem may be sharply angled, or more or less rounded. The stems do not have nodes (knobbly knees!) and are typically filled with pithy tissue inside and not hollow.

The leaves of true sedges are flattened like grass leaves but in many species they are slightly pleated such that they for an 'M' when viewed in cross-section. They often have minute teeth along the margins and are mostly basal, forming dense clumps, or appearing in scattered, small rosettes from creeping roots. The leaves clasp the stem at their bases and typically have a membranous, sheathing, lower section that wraps right around the stem. Unlike grasses, these sheaths are not split down one side so the leaf cannot be pulled away from the stem without splitting the sheath.

The flowers appear at or towards the top of leafless stems and are held above the basal leaves. In most sedges, most flowers are either male or female (i.e. contain either stamens or a stigma, but not both), with male flowers typically towards the top and female flowers lower down. The flowers are carried close to the main stem and not in open, spreading panicles. Flowers may be all contained in a single, tight cluster, or may have several clusters spaced out along the upper part of the stem. Flower clusters are each accompanied by a bract which is often leaf-like.

The individual flowers within the spike all have their own small bract (called a glume) behind which they sit and are often partially hidden. Male flowers have two or three stamens while female flowers have two or three stigmas and eventually produce a small nutlet that is completely surrounded by an extra bract which is known as the utricle. The flowers effectively have no petals or sepals.

Sedges - growth style


Tight tussocks of arching leaves and upright flower stems	spreading patches of tall stems and leaves	spreading patches of low stems and leaves	Single spikes just a few centimetres in height

Sedges - stems


Stems three-sided	Angled corner of stem	Stem at leaf base	Stem and back of leaf

Sedges - leaves


Leaf bases surround stem with a membranous sheath	Leaf has a membranous sheath where it joins the stem	Leaves flat and grass-like	Leaves sometimes pleated and 'M'-shaped in cross section

Sedges - flowerheads


Elongated, well spaced, upright spikes	Contracted spikes of rounded clusters	Densely packed spikes	Pendulous spikes

Sedges - flowers


Typical spike with male flowers above, female flowers below	Anthers protruding from upper, male flowers	Female flowers with stigmas in threes	Male flowers with strongly marked bracts

Sedges - fruits


Typical spike with old male flowers above and female flowers developing fruits below	Prominent green fruits with brownish bracts (glumes)	Typical dense spike with spreading fruits	Pendulous fruit clusters

Sedge Allies

With the sedges covered above, the rest of the family Cyperaceae is covered here and these plants are referred to as the 'sedge allies' - species that are in the same family as the Carex species, but which differ in some key ways in their appearance. Because this group covers a diversity of species, there is quite a variety in the appearance of these plants, ranging from tiny wetland plants that are no more than a few centimetres high, to plants that can form large colonies, up to two metres in height.

The leaves may be flattened like grass leaves (often with minute teeth along the margins), or the leaves may be absent with the plant then consisting of a cluster of upright, rounded stems, rather like the rushes; indeed, some have 'rush' as part of their name, even though they are not true rushes.

As with the true sedges, the flowers appear at or towards the top of leafless stems and are held above any basal leaves that might be present. However, unlike true sedges, most flowers are bisexual, with both male and female parts present. The flowers may be in open, spreading panicles or all contained in a single, tight cluster. Flower clusters are typically accompanied by a bract which may or may not be leaf-like. In most species, these flower clusters are reddish-brown to chocolate-brown, but may also be creamy white.

The individual flowers within the spike all have their own small bract (called a glume) behind which they sit and are often partially hidden. They typically have three stamens and two or three stigmas, though there is a little variation in this. The flowers effectively have no petals or sepals. They eventually produce a small nutlet that is exposed and not surrounded by a utricle; these nutlets are often very small, requiring a hand lens or binocular microscope to view their features.

Sedge Allies - growth style


Tall leafless stems, forming colonies standing in water	Tall, tight clumps of stiff, upright stems	Low, spiky clusters with white flowerheads	Leafless spikes just a few centimetres in height

Sedge Allies - stems & leaves


Leaves may be broad and sedge-like, with saw-toothed edges	Stems may be rounded, with a 'collar' towards the base

Sedge Allies - flowerheads & flowers


Heads of flattened spikelets	Tight heads of rounded clusters	Tight heads with long, leafy bracts	Clusters of drooping spikelets

Clusters of white spikelets	Open heads of rounded clusters	Narrow, tight heads at the top of leafless stems	Clusters of flattened spikelets

Sedge Allies - fruiting heads


Leaves may be broad and sedge-like, with saw-toothed edges	Typical tight cluster of bracts with nutlets hidden within	Typical tight cluster of bracts with nutlets hidden within	Fruiting head with long, cottony hairs

To continue to grasses, click here.

Flora of East Anglia An Identification Guide