Triangular Club Rush

Triangular club-rush is a perennial species (4) that seems to be able to tolerate brackish (slightly salty) water, but may fare better if freshwater flows around the rhizomes (2). It rarely produces seed in the wild in Britain and Ireland, but does so readily in cultivation and in Europe (and probably elsewhere) (6).

Triangular club-rush is a UK Biodiversity Action Plan priority species, and a Species Action Plan has been produced to coordinate conservation efforts. The Environment Agency is the lead partner for this species and has carried out a number of measures with English Nature and Royal Botanic Gardens Kew, including the enhancement of the remaining plants on the River Tamar. In addition an ex-situ programme has been established at Royal Botanic Gardens, Kew (4). Future plans include continued monitoring, and genetic studies to investigate whether reintroduction programmes are suitable (4).

Triangular club-rush is a critically endangered species in Britain. Both the common name and the Latin name triqueter (from the Latin triquetrus meaning three-cornered) (3) refer to the cross-sectional shape of the hairless stems, which have three corners (1). The plant mainly spreads by means of creeping rhizomes in Britain (6), and produces flowers at the top of the stem in groups called spikelets, which are in turn arranged in clusters known as inflorescences (1).

In Britain and Ireland it is restricted to the upper parts of tidal rivers where there are weakly brackish to fresh water conditions and large fluctuations in water level (at very high tides the plants may be submerged), but it occurs in a variety of wetlands and fresh water ecosystems elsewhere in the world (6). It is even a weed of paddy fields in Asia (6).

This species was first found in 1650 on the River Thames (4), and it has since been recorded from several sites, all in the south of England, including the River Medway in Kent, the Tamar in Devon and Cornwall, and the Arun in West Sussex. Following a severe decline the species is now known only from the River Tamar in Devon, where it exists as just one or two small clumps (6). In Ireland it has been recorded in three rivers, and although gone from one river, it still has a large and apparently stable population on the Shannon (6). It is a very widespread species, which is locally abundant in the tropics and becomes rarer further north. It is recorded from west, central and southern Europe through western, central and eastern Asia to Japan and the Philippines, and in north Africa (recorded once on the Suez canal only) and South Africa. It is so prolific in some areas that control with herbicides is required. It occurs from sea-level in many parts of the world to an altitude of at least 2400 m in Kashmir (6).

Classified as Critically Endangered in Great Britain and fully protected under Schedule 8 of the Wildlife and Countryside Act 1981 (2).

The three main causes of the decline in Britain appear to be direct loss of habitat due to construction of river embankments, growth of common reed, and failure to recolonise after indirect changes in the river flow patterns resulting from river engineering, canalisation, etc., which cause erosion of the river banks and the subsequent loss of colonies (6). Increased flow rates resulting from extensive drainage of the catchments may contribute to changing water flows. Furthermore, increased sedimentation rates due to high sediment runoff from ploughed fields may have changed deposition and erosion patterns. There is no direct evidence that water pollution, wash from boat traffic, collection by botanists or hybridisation has caused decline. The species is probably not under threat world-wide (6).

Just like most sedges, triangular club-rush has a three-sided stem. But in this case, the edges are very pronounced. Don't let the name fool you, it is not a rush species. Triangular club-rush is a very sturdy plant and is resistant to waves. It used to be one of the characteristic pioneer plants on the freshwater marshes in the Belgium-Dutch delta. Pollution and faulty management of river banks in the past have resulted in this plant practically disappearing. Now that the rivers are being cleaned up, triangular club-rush is slowly returning.

In North America Schoenoplectus triqueter is known only from the tidal Columbia River system (B. W. Lightcap and A. E. Schuyler 1984), where it forms fertile hybrids with S. tabernaemontani [S. ×kuekenthalianus (Junge) D. H. Kent = Scirpus ×scheuchzeri Brugg]. Fertile hybrids between the same species also occur in Europe.

Rhizomes 1.5–5 mm diam. Culms sharply trigonous, 0.5–1.5 m × 2–4 mm. Leaves 3–4, basal, smooth; sheath fronts not pinnate-fibrillose; blades 1 or 2, thickly V-shaped in cross section, to equaling sheath length. Inflorescences 1–2 timesbranched or subcapitate or of 1 spikelet, branches to 4 cm; proximal bract usually erect, trigonous, 2–7 cm. Spikelets 1–35, in clusters or solitary, 5–12 × 3–4 mm; scales straw-colored to orange-brown or midrib greenish, usually clearly lineolate-spotted, ovate, 3–3.5 × 2.5 mm, flanks ribless, midrib proximally spinulose, apex acute to rounded, notch 0.3 mm deep, awn 0.3 mm, sparsely spinulose. Flowers: perianth members 4–6, brown, bristlelike, equaling to less than 1/2 of achene body, retrorsely spinulose; anthers 2 mm; crest short, spinulose; styles 2-fid. Achenes brown, biconvex, ovoid to obovoid, 2–2.5 × 1.5–2 mm; beak 0.1–0.2 mm. 2n = 42.

Perennial, 50-125 cm. Rhizome creeping or stoloniferous, 2-4 mm diam., brown or reddish brown. Stem 2-6(-10) mm diam., distal parts sharply, proximal parts obtusely trigonous, smooth, glaucous green. Sheaths 3, ephemeral, green or often with reddish tint, mouth deeply oblique, margins widely scarious; blades mostly reduced to mucro, uppermost up to 50 mm, channelled, smooth, apex obtusely pointed. Inflorescence of (1-)3-7 sessile spikes, 15-25 mm diam., or a multiple spike; lowest bract to c. 35 mm, trigonous, smooth; primary branches 0-7, up to 30 mm, each with (1-)2-4 sessile spikes; secondary branches occasional, up to 8 mm. Spikes 8-12 x 4-7 mm, ovoid; glumes rather loosely imbricate, 3-4.1 mm, cymbiform, mid-nerve mostly smooth, mucro barbed, up to 0.8 mm, sides inconspicuously nerved, brown or yellowish brown, smooth, apex rounded, often truncate, margins scarious, ciliate. Perianth bristles 4-6, about equalling nut; stamens 3, anthers 1.5-2 mm; stigmas 2. Nut 2.2-3.2 x 1.3-2 mm, ellipsoid or ovoid, bi-convex or almost plano-convex, smooth, yellow brown, glossy.

introduced; Oreg., Wash.; Eurasia.

Distribution: Europe to Japan, China and Taiwan, from Caucasus to Tadjikistan, Pakistan and N. India; Egypt, S. Africa.

Fl. Per.: May - July.

Fruiting summer.

Alluvial meadows, by rivers and lakes, rice fields.

Freshwater tidal shores, marshes, dredge spoil; 0m.

Scirpus triqueter L., Mant. Pl. 1: 29. 1767; C. B. Clarke, l.c. 658; R. R. Stewart, l.c. 104.

Scirpus triqueter Linnaeus, Mant. Pl. 1: 29. 1767