Carex chordorrhiza

Carex chordorrhiza L. (Cyperaceae) 

String sedge, Seisg Shreangach

Status in Britain: VULNERABLE.

Status in Europe: Not threatened.

C. chordorrhiza is known from only two sites in Britain, both in the Highlands of Scotland. On the Insh Marshes in Strathspey, it occurs in fens dominated by Carex rostrata, Equisetum fluviatile, Menyanthes trifoliata, Potentilla palustris and, more rarely, in mires dominated by C. rostrata containing Sphagnum squarrosum. At Altnaharra, Sutherland it is found in similar mire communities dominated by Sphagnum recurvum. These types of community are frequent in Scotland, and C. chordorrhiza may be a glacial relict (Matthews 1955). The pH of water samples from the two Scottish sites ranges from 5.4 to 6.5 and represents the upper range for this species in Europe. This species tolerates temporary submergence as, for instance, during winter flooding of the Insh Marshes (Legg, et al. 1995). Many of the populations of C. chordorrhiza at Altnaharra may, however, avoid submergence by floating to the surface together with the substrate.

C. chordorrhiza is an extensively creeping perennial often producing very long, trailing stems or runners between short upright tufts of fine bright green leaves. Plants flower during May, and the few seeds that are set are shed from July onwards. Regeneration is mainly clonal, with runners up to 100 cm long produced from early August. Fragments of plant dislodged by disturbance may be the main means of dispersal, and propagation by seed relatively unimportant. There is, however, considerable genetic variation in both populations (A. Hamilton, pers. comm.) indicating that at least some reproduction by seed takes place.

The smaller population at Altnaharra was first discovered in 1897 and since then appears to have remained relatively unchanged in size. The species was discovered at Insh in 1978 (Page & Rieley 1985) and the large populations there were extensively mapped in 1989 (Wood 1989). A repeat sample survey during 1994 indicated that the known area covered by this species had increased five-fold (Legg, et al. 1995), with evidence of both population expansion and under-recording. The presence of many old drains which are now derelict implies that the marsh may have been drier, but reverted to a wetter condition under current management, and this could explain the observed expansion of this sedge.

Populations in both of its localities are large and vigorous and are likely to remain so under current management. The main threat comes from proposals to drain the Insh marshes to control flooding in the Spey and, conversely, to flood the Altnaharra site to regulate water flow in the Naver. Experimental work has shown that C. chordorrhiza does not survive prolonged inundation; the few plants that survived grew very little and suffered high levels of shoot mortality (Legg, et al. 1995). Clearly a reduction in water table is also likely to result in significant changes to the fen and mire communities in which this species is found. 

C. chordorrhiza has a circumpolar distribution and is abundant in Fennoscandia, Iceland, north-west Russia, Poland and northern Germany, especially around the Baltic. Elsewhere in Europe it is uncommon, extending south to the Pyrenees and central Ukraine. It also occurs sporadically in arctic-boreal zones of northern Russia, and in North America from Greenland to Alaska southwards to Indiana (Hultén & Fries 1986). In Europe it is a constituent of small-sedge or transition mires (Page & Rieley 1985). It will colonise into Sphagnum nuclei developed in this vegetation, or denser vegetation of taller Carex species or sparse Phragmites australis.

N. R. Cowie