Rushes - Juncus spp

Sedges have edges, rushes are round
And grasses are hollow right down to the ground

This mnemonic for distinguishing between sedges, rushes and grasses is worth remembering, even though there are plenty of exceptions to the rule (usually non-Carex spp sedges).

Rushes Juncus spp are fairly easily recognisable even for non-botanists. They have rather rigid tubular leaves and stems, brown flowers / seed heads and grow in dampish places. To identify them to species level you need to know:
  • if the leaves are hollow or filled with pith (a sort of spongey material). You need to neatly cut them transversely or lengthwise to see.
  • whether the leaves are 'jointed' ie running your fingers up the leaves reveals a ladderlike construction inside. You can feel the crossbraces inside the leaf.
  • if the leaves are smooth or grooved. If grooved they may be finely fluted all the way around like a tiny Greek column, or they may be sort of folded in half, forming a groove down one side. You can feel for grooves by rolling a leaf in your fingers or look at them with a magnifying loup.
  • how the flowers are arranged and what the seed capsules look like - match them in a good field guide such as the Colour Identification Guide to the Grasses, Sedges, Rushes and Ferns of the British Isles and north-western Europe by Francis Rose.
They can range in size from the well known pond edge and damp pasture species that are usually 40 - 60 cm high, to small plants that grow on open ground such as pathways and in lawns and only reach 2 - 10 cm high.
Sharp-flowered Rush J. acutiflorus: This species is one of the jointed rush group, with hollow stems that are cross partitioned inside. The red brown flowers are in loose bunches on the ends of the stems. The stems are 30 - 100 cm high, with 2 - 4 deep green round leaves each, growing in erect patches. The seed capsules are a fine cone shape, very pointy and surrounded by sharply pointed perianth segments which arch outwards at the point. Common and abundant in fens, bogs, wet meadows or woods, favouring somewhat acid soils. Flowers July - September. Below, photographed in the drawdown zone of the Etang de Ribaloche in the Foret de Preuilly, June. In the second photo you can see the joints in the stems.

Soft Rush J. effusus: This species is one of a group that appears to flower from the side of the stem (in fact, the 'stem' above the flowers is a bract). The leaves are reduced to brown sheaths at the bottom of the stems. It is erect and forms dense tufts, tall (30 - 150 cm) and robust. The stems are green, filled with pith and feel smooth (although in fact they are very finely fluted). The seed capsule is egg shaped, brown, with a dimple in the top. Very common in damp grassland, marshes, bogs and wet open woods. Flowers June to August. Photographed, below, in the draw down zone of the Etang de Ribaloche in the Foret de Preuilly during the drought of 2011. In dry conditions like this it can look very like its close relative Compact Rush J. conglomeratus.

No comments:

Post a Comment