Spike-rushes and Allies
What are they?
The plants on this page are all members of the Sedge Family (Cyperaceae) but all differ from the sedges in the genus Carex in having perfect flowers, i.e. flowers that bear both male and female parts. Typically, the female stigmas mature first, with the stamens following later and there may sometimes be an overlap between the last stigmas and first stamens within a spikelet of flowers. In this group, the flowers are greatly reduced, rather like they are in the grasses. Each flower has a single bract at its base, accompanied by the stamens and stigma. The remains of a perianth (what would be the petals and sepals in many flowers) often exist as a series of small bristles at the base of the flower.
These plants are closely related to the club-rushes and cottongrasses but differ in having a single, terminal spike of flowers.
Where are they found?
The great majority of plants in this group are wetland species and can be found in wet habitats or, often, growing within the margins of standing water in fens and mires.
Identification
The various genera within this broad group of plants are different enough from each other to be easy to tell apart from the photographs. However, within the genera, careful attention to detail of the flower or fruit structures is sometimes required. This may require a microscope as the fruits in particular are very small, so it may be necessary to take a small sample home for later study. Small portions of a flower cluster can be removed without the need to take large quantities.
In the Eleocharis species, it is important to check details of the lowest flower bract (or glume) in the flower spike, the number of flowers in the spike (which can be determined by counting the visible bracts) and the number of stigmas in a flower or the shape of the nutlet. In some species, you may need to check the number of perianth bristles - tiny, hair-like structures that can best be seen at the base of the nutlet after flowering has finished.
Common Deergrass Trichophorum germanicum
Native. Although a common plant on upland moorland elsewhere in the UK, this is a very rare plant in East Anglia, confined to around five sites in Norfolk on wet heath and bogs. Flowers May to June. Plants 5-40cm in height, forming dense tussocks of tough and wiry, upright stems. Leaves in a basal tuft with stem leaves small and bract-like. Flowerhead a terminal spike, 3-6mm long with 3-20 flowers.
Rather similar to the Eleocharis spike-rushes and best told from them by the uppermost leaf sheath, which has a short (3-10mm) but noticeable blade pressed close to the stem.
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Common Spike-rush Eleocharis palustris
Native. Common and widespread in wetlands throughout the region, often forming dense swards around the margins of seasonally wet pools and damp hollows. Flowers May to July. Plants 10-75cm in height, forming spreading colonies of wiry, upright stems. Leaves reduced to just their sheaths, appearing as ring-like structures around the stems. Flowerhead a terminal spike of 10 or more flowers, 5-30mm long with the lowest flower bract not fully encircling the base of the spike and the two lowest bracts without flowers. Stigmas 2, nutlet bi-convex with 0-4 perianth bristles.
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and anthers mature |
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Many-stalked Spike-rush Eleocharis multicaulis
Native. Rare, occurring at less than 10 wetland sites on neutral to acidic soils. Flowers May to July. Plants 15-40cm in height, forming tight tussocks of upright stems. Leaves reduced to just their sheaths, appearing as ring-like structures around the stems. Flowerhead a terminal spike of 10 or more flowers, 5-15mm long with the lowest flower bract not fully encircling the base of the spike and only the lowest bract without a flower. Stigmas 3, nutlet three-sided with 4-6 perianth bristles.
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Slender Spike-rush Eleocharis uniglumis
Native. Widespread but uncommon with a few inland records but also found in coastal wetlands, even brackish areas. Flowers May to July. Plants 10-60cm in height, forming spreading colonies of wiry, upright stems. Leaves reduced to just their sheaths, appearing as ring-like structures around the stems. Flowerhead a terminal spike of 10 or more flowers, 5-12mm long with the lowest flower bract more or less encircling the base of the spike and only the lowest bract without flowers. Stigmas 2, nutlet bi-convex with 0-4 perianth bristles. This species often has spikes that lean strongly to one side when fruiting.
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Few-flowered Spike-rush Eleocharis quinqueflora
Native. Rare, occuring in peaty, calcareous fens at a few, isolated locations in Norfolk and on the Norfolk/Suffolk border. Flowers June to July. Plants 10-30cm in height, forming tufted colonies of wiry, upright stems. Leaves reduced to just their sheaths, appearing as ring-like structures around the stems. Flowerhead a terminal spike of 3-12 flowers, 4-10mm long with the lowest flower bract more or less encircling the base of the spike and more than half the length of the spike. Stigmas 3, nutlet roundly three-sided with 4-6 perianth bristles.
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Needle Spike-rush Eleocharis acicularis
Native. Rare, but tiny and perhaps overlooked. Sporadically reported from wetlands in our region but mostly recorded from the southern and western edges of The Fens. Flowers July to September. Plants to 10cm in height, forming tufted colonies, sometimes carpeting bare mud in favoured places. Leaves reduced to just their sheaths, appearing as ring-like structures around the stems, but some lower stems without flower spikes can appear like leaves. Flowerhead a terminal spike of 3-12 flowers, 2-5mm long with the lowest flower bract more or less encircling the base of the spike and about half the length of the spike. Stigmas 3, nutlet roundly three-sided with 0-1(4) perianth bristles.
A minuscule plant, spreading by creeping, perennial stems that produce tussocks of flowering stems at interval along the stem.
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Bristle Club-rush Isolepis setacea
Native. Uncommon but widespread and perhaps overlooked due to its size, in seasonally wet patches on heaths and sandy places. Flowers May to July. Tiny annual plants, germinating in the autumn. Stems 2-15cm in height, forming tight tufts. Leaves hair-like, deeply channelled above. Flowerhead a terminal spike of 1-4 (sometimes more) spikelets, the spikelets 1.5-5mm long and the whole spike accompanied by a spike-like bract that is usually longer than the flower spike. Nutlets longitudinally ridged.
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Slender Club-rush Isolepis cernua
Native. Rare but perhaps overlooked due to its size, in seasonally wet patches on heaths and sandy places. Flowers May to July. Tiny annual plants, germinating in the autumn. Stems 2-15cm in height, forming tight tufts. Leaves hair-like, deeply channelled above. Flowerhead a terminal spike of 1-2 spikelets, the spikelets 2-4mm long and the whole spike accompanied by a spike-like bract that is usually shorter than the flower spike. Nutlets not ridged but very finely covered in small bumps.
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Floating Club-rush Eleogiton fluitans
Native. Rare, with most records coming from the Norfolk Broads, but a few scattered elsewhere. Typically in standing water, either submerged or floating out across the water surface from the margins. Flowers June to August. Stems creeping or floating and rooting at the nodes where they touch land. Leaves grass-like with sheathing bases, the sheaths often remaining after a leaf has withered. Flowerhead a terminal spike of one spikelet, 2-5mm long and with 3-5 flowers. Nutlets pale whitish or yellowish.
A strange plant, easily passed off as a grass and only recognised as a member of this group by its flowers.
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Common Flat-sedge Blysmus compressus
Native. A scarce and declining species of wet meadows and fens, probably suffering from lowering water tables and nutrient enrichment of the land from agricultural run-off. Flowers June to July. Plants to 45cm in height. Leaves flat, keeled, grass-like with sheathing bases. Flowerhead a terminal spike with 10-25 spikelets arranged in a double row, flattened in one plane. Nutlets 1.5-2mm long.
More closely related to the galingales, but more like the spike-rushes in overall appearance, so placed here for identification purposes.
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