Identifying grasses

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Identifying grasses

Grasses are technically known as Gramineae (but occassionally as Poaceae) and are arguably the most important plant family in the world.

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Plant family groups

Meadow fescue Festuca pratensis © Ita McCobb

According to the Royal Botanic Gardens, Kew, London and the Missouri Botanical Garden, all plant families can be divided into four main groups:

  • Flowering plants (Angiosperms)
  • Conifers, cycads and allies (Gymnosperms)
  • Ferns and fern allies (Pteridophytes)
  • Mosses and liverworts (Bryophytes).

Grasses, Sedges and Rushes all belong to the same plant family, that of Flowering plants (Angiosperms) and so are frequently confused with each other as they often have very similar characteristics. An old saying that often helps differentiate them – although it is not always accurate – is: “Sedges have edges, rushes are round and grasses are hollow right up from the ground!”

Normally Grasses have cylindrical, usually hollow stems with nodes (swollen joints), alternate leaves (appearing in pairs) and flowers.

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Grass forms

Nodding melick Melica nutan © Ita McCobb

Grasses are what we call “Monocotyledons”, which means they have a single (mono), embryonic first leaf that appears from a germinating seed. A “Cotyledon” is the first leaf produced by a seed-bearing plant. The other term you may come across in this respect is “Dicotyledons” – which means a plant has two (di) embryonic first leaves appearing from a germinating seed.

Grasses tend to form in either dense clumps or tufts. They usually have erect, hollow stems with swollen joints (called nodes) – which we used to love chewing on as kids – and alternating leaves in twos borne along the length of the stem.

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Grass root systems

Perrenial ryegrass Lolium perenne © Ita McCobb

The root systems of Grasses come in several different forms. Some have long underground stems (called rhizomes), others aerial stems that grow from small swollen bulbs and yet others that produce creeping, leafy stems or “stolons” above ground.

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Grass reproduction

Cock's-foot Dactylis glomerata © Ita McCobb

In order to reproduce Grasses need to be pollinated, which is why Grasses evolved in a way that helps their pollen transfer easily by wind from one plant to another or, in the case of self-pollinating Grasses, within the same plant. As most hay-fever sufferers are aware, grasses produce and distribute huge quantities of very light, dust-like pollen. On the receiving side, that part of the grass that receives the pollen (called the stigma) is large, feathery and sticky so that it can easily catch the pollen as it passes through the air.

Once pollinated, Grasses produce fruit, but unlike other plants, where the difference between the fruits that normally contain the seeds is very obvious, in Grasses this difference is barely noticeable since the fruits of Grasses are very dry and hard and contain only one seed, which is merged with the wall of the fruit.

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Examples of common names for wild grasses

False oat-grass Avenula-pubescens © Ita McCobb

Nit grass, Hairy-finger grass, Common cord-grass, Purple moor-grass, Meadow foxtail, Wood millet, Purple small-reed, Yorkshire fog, Loose silky-bent, Nodding melick, Meadow barley, Couch grass, Lesser hairy brome, Quaking grass, Cock’s-foot.

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References: Botany for gardeners, Brian Capon, Third edition, Timber Press; Colour Identification Guide to the Grasses, Sedges, Rushes and Ferns
of the British Isles and north-western Europe, Francis Rose, Viking, The Penguin Group; Latin for gardeners, Lorraine Harrison, Royal Horticultural Society; Oxford English Dictionary, Oxford University Press.