Graminoid herb forming loose mats from a branched rhizome system. Rhizomes coarse, 3–4(5) mm broad, with purplish black leaf sheaths, branch lengths 2–20 cm. Leafy shoots 7–20 cm tall, ascending from rhizome. Culms 15–17 cm, smooth, about as tall as leafy shoots or shorter.

Leaves folded or revolute (slightly M-shaped in cross section), 10–17 cm long, 3–4(5) mm broad at the base, ending in a narrow tip, densely papillose on lower surfaces, margins and dorsal mid vein scabrous, medium green on both sides. Base of leaf sheaths dark red or purplish.

The flower in Carex is unisexual (either male or female), without perianth, and supported by a scale (the bract of the single flower). The male flower consists of 3 stamens. The female flower consists of a gynoecium of 2 or 3 fused carpels, with a single style and 2 or 3 stigmas, and with a single seed. The gynoecium is surrounded by a perigynium, a container with a narrow apical opening through which the style and stigmas emerge. The perigynia (and nuts) are either lenticular (when two carpels/stigmas) or trigonous (when three). The inflorescences are spikes, one or more per culm. If two or more spikes, all except for the uppermost are supported by more or less leaf-like bracts. Spikes may be unisexual or bisexual, and bisexual spikes may have the female flowers at base (basigynous) or at top (acrogynous). Flowers are wind pollinated and usually cross pollinated because the male flowers reach anthesis before the female flowers (protandry). Cross pollination predominates among sedges investigated in alpine Norway (Berggren & Haugset unpubl.), either due to the protandry or to genetic incompatibility. Seeds are spread inside their perigynia.

Inflorescence of 3 or more erect spikes, 1 terminal male, 2 or more lateral female. Bracts usually exceeding the spikes; bract of lowermost spike with sheath ca. 1 mm at base and blade 6–7 cm long and 3 mm broad, narrowing into an acute apex; bracts of upper spikes shorter and narrower. Male spike 1.5–2.5 × ca. 0.4 cm on ca. 2 cm long pedicel, erect. Female spikes 2 cm long (Svalbard) or longer (North American material), ca. 0.4 cm broad, on ca. 0.5 cm long pedicels, erect, with more than 50 flowers per spike. Scales ovate, obtuse, dark brown with a narrow, dark or pale brown mid vein and a narrow, light brown or hyaline margins. Scales of male spikes more elongated than those of female spikes. Perigynia lenticular, papillose, smooth at margin, pale brown with a darker upper part and ca. 0.2 mm dark beak, aperture more or less truncate. Stigmas 2.

Lenticular nut within the perigynium.

Sexual reproduction by seeds, potentially; efficient local vegetative reproduction by the rhizome system. The only collections of C. concolor from Svalbard were collected 19. Aug. 1928 and are in flowering stage. Thus, this observation combined with the lack of records of the species from elsewhere in the archipelago indicate that sexual reproduction is very rare if it reproduces at all.

Fruits (inside perigynia) are usually dispersed with water and most probably birds.

The section Phacocystis includes three species in Svalbard: Carex bigelowii, C. concolor and C. subspathacea. Carex subspathacea differs from the two others in very short culms and leafy shoots that are clearly longer than the culms, in fewer flowers in each spike, and in reddish brown scales and perigynia (at least in mature stage). Carex concolor differs from C. bigelowii, e.g., in much broader rhizomes and leaves and in bracts shorter than inflorescence.

There is no information about the habitat of this species in Svalbard but the site information, at the margin of a broad river plain, suggests wetland or wet tundra. The species is generally rather indifferent as to soil reaction (pH) but prefers circumneutral or basic soils. The substrate in Forkdalen is uniformly basic.

Only found once at one site in Svalbard, “Munningen av Forkdalen sydgren” (mouth of the southern part of the valley Forkdalen), Wijdefjorden, Andrée Land, in the middle arctic tundra zone and at the boundary between the weakly and the clearly continental sections.

Carex concolor has variously been considered a species closely related to C. aquatilis Wahlenb. (most often by the name C. stans), or as a race of that species, by European authors most often as C. aquatilis ssp. stans (e.g., Chater 1980 and Lid & Lid 2005), by recent American authors as C. aquatilis var. minor (e.g., Standley et al. 2002). The name C. concolor has replaced C. stans at the rank of species due to priority (the name ‘concolor’ is 18 years older). Several recent genetic studies suggest that the variation in C. aquatilis s. lat. and its relatives is complex and not readily fitting into the existing model. Support for a solution where C. aquatilis and C. concolor are considered two different species is found in studies by, e.g., Dragon & Barrington (2008, 2009), Nakamatte & Lye (2008), and Gebauer et al. (2014).

The presence of Carex concolor in its single known site in Svalbard is most probably due to fortuitous bird dispersal. This is a large-grown and easily visible species, and the probability that it is much overlooked is negligible. It is also a hardy species, reaching the northern arctic tundra zone regularly in Canada, Greenland and Russia. The alternative hypothesis, i.e., that is has had a larger range in the warmer parts of the Postglacial (the Hypsithermal) is not very convincing for just this quite hardy and ecologically indifferent species. The explanation why it has not spread farther from its Forkdalen site (not even to other parts of Forkdalen) may be found in self incompatibility.

Chater, A.O. 1980. Carex L. – In: Tutin, T.G. et al. (eds.), Flora Europaea. 5. Alismataceae to Orchidaceae (Monocotyledones): 290–323.

Dragon, J.A. & Barrington, D.S. 2008. East vs. west: Monophyletic clades within the paraphyletic Carex acuta complex, section Phacocystis (Cyperaceae). – In: Naczi, R.F.C. & Ford, B.A. (eds.), Sedges: uses, diversity, and systematic of the Cyperaceae: 215–226.

Dragon, J.A. & Barrington, D.S. 2009. The systematics of the Carex aquatilis and Carex lenticularis lineages: geographically and ecologically divergent sister clades of Carex section Phacocystis (Cyperaceae). – American Journal of Botany 96: 1896–1906.

Gebauer, S., Starr, J.R. & Hoffmann, M.N. 2014. Parallel and convergent diversification in two northern hemispheric species-rich Carex lineages (Cyperaceae). – Organisms Diversity & Evolution 14: 247–258.

Nakamatte, E. & Lye, K.A. 2008. AFLP-based differentiation in north Atlantic species of Carex sect. Phacocystis. – Nordic Journal of Botany 25: 318–328.

Standley, L.A., Cayouette, J., & Bruederle, L. 2002. Carex Linnaeus sect. Phacocystis Dumortier. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 23. Magnoliophyta: Commelinidae(in part): Cyperaceae: 379–401.