This tussock-forming, rhizomatous perennial herb occurs on mud-banks along the lower reaches of tidal rivers, where it may become submerged at the highest tides. Lowland.
Populations of S. triqueter have been lost to land reclamation and as a result of bank construction. The surviving population on the River Tamar (S. Devon) is now extremely small, although the hybrid with S. tabernaemontani is more frequent there. S. triqueter is still present in Ireland by the River Shannon (Co. Limerick) and its tributaries, where populations are larger than in Britain but some are threatened by development.
Eurasian Temperate element.
Count of 10km squares in Great Britain: 8
Count of 10km squares in Ireland: 3
Count of 10km squares in the Channel Isles: 0
RDB Species Accounts
Schoenoplectus triqueter (L.) Palla (Cyperaceae)
Scirpus triqueter L.
Status in Britain: CRITICALLY ENDANGERED. WCA Schedule 8.
Status in Europe: Not threatened.
S. triqueter grows on mud banks along the lower reaches of tidal rivers. It forms clumps on the river-ward edge of fringing beds of Phragmites australis along with other Schoenoplectus species. The mud on which it grows is exposed at low tide, but the plants may become completely submerged, at least by the highest tides. It is tolerant of brackish conditions, but is not found in association with any true halophytes. It may be favoured by freshwater seepage around its roots and, by the Tamar, Agrostis stolonifera and Oenanthe crocata grow nearby.
This species is a perennial, flowering from July to September, about one month later than other Schoenoplectus species and somewhat later than the hybrids. However, the last remaining plant of this species in Britain is reported to flower poorly and erratically, and fruit-set has not been observed in the wild in Britain or Ireland.
At one time this species occurred in the Tamar (Devon and Cornwall), Arun (West Sussex), Medway (Kent) and Thames (Greater London). It is now restricted to the Tamar, Devon, but even here it appears to be on the verge of extinction. In 1985, surveys revealed six patches covering about six square metres, but in 1989 and 1994, only four clumps covering two square metres were detected. It is believed that, in 1996, only a single unhybridised clump remained, in which case this may now be the rarest vascular plant in Britain. The hybrid with S. tabernaemontani (S. x kuekenthalianus) is still very locally frequent on the Tamar and occurs in small quantity on the Arun and Medway. The hybrid with S. lacustris (S. x carinatus) has also been recorded from the Tamar, and from the Thames (Jackson & Domin 1908; Lousley 1931), but is now very rare or extinct (Stace 1997).
Both S. triqueter and S. x carinatus were once locally frequent by the Thames. It disappeared gradually over a period of at least 50 years as a result of land claim and work on river embankments, and was last seen in about 1946 (Lousley 1976). Similarly, the Medway population of S. triqueter disappeared in about 1940, following works to make the river more navigable, and records of it in recent years are erroneous (only S. x kuekenthalianus remains). River engineering contributed to its extinction on the Arun, but mudbanks are still common by the Tamar, and reasons for the decline of S. triqueter there are unclear. The hybrid S. x kuekenthalianus has been present at least since the end of the nineteenth century and there is no evidence to suggest that there is significant competition between it and S. triqueter.
This species is widely distributed across central and southern Europe, extending to western Asia and North Africa, and occurring also in North America and South Africa. It becomes local in the northern parts of its range and is absent from Scandinavia. It seeds readily in warmer climates, but does not appear to do so in the wild in the north. It may also be less able to compete vegetatively in northern areas because of the cooler climate, and in these areas is normally restricted to habitats where competition with other swamp species is reduced.
N. F. Stewart
PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.