Graminoid herb growing in dense mats with extensive, densely branched rhizome. Rhizome segments thin, with brown prophylls (see below) with very distinct veins, typically with short distances (0.5–2 cm) between aerial shoots and resulting in an often dense, sometimes tussock-like sward. Aerial shoots with 1–3 prophylls (reduced basal leaves without, or sometimes with a very short blade). Culms slender, 4–8 cm long, 0.7–1 mm broad, ascending, curved or straight, with 3–5 basal leaves, obscurely trigonous, smooth, not papillose, green with distinct, pale ribs.

Leaves filiform (involute), 3–5 cm long, shorter than culms, slender, 0.4–0.7 mm broad, mid vein slightly raised on lower surface, margins minutely serrate or scabrous for much of their length, not papillose, greyish green.

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).

Inflorescence a dense, narrow cluster of 2–4 spikes, 8–10 × 3–5 mm. Top spike oblong, 5–9 × 3–5 mm, with 7–10 female flowers at base and at top some not developed male flowers (basigynous). Lateral spikes similar but much smaller, with 1–4 female flowers. Lowermost bract ca. 5 mm, brown with a white or yellowish hyaline margin, occasionally with a blade 1–3 mm. Scales 3–5 × 1–1.4 mm, ovate, subacute, brown with a diffuse, white or yellowish hyaline margin. Perigynia lens-shaped (lenticular with one nearly flat and one convex side), narrowly elliptic, 2.5–4 × 0.4–0.8 mm, with a very small foot, tapering very gradually into a 0.5–0.8 mm beak, aperture oblique truncate (the stigmas appearing at the side of the apex), with indistinct veins, smooth (also on the beak), dark brown. Stigmas 2. Never observed with stamens.

Fruit not fully developed in the studied specimens; immature fruits remaining in the spike into the next season. If developed, it would be a lens-shaped (lenticular) nut enclosed in the perigynium (the dispersal unit).

Slight local vegetative reproduction by rhizome growth and possibly fragmentation. No seed reproduction known. Carex lidii has been assumed to be the sterile hybrid between C. maritima and C. parallela, both proposed parent species growing in often extensive mats with horizontal, richly branched rhizomes. Like in its assumed parents, the stands of C. lidii may be very long-lasting (easily centuries, perhaps millennia) and can be fragmented by soil movement (frost action). This way of growth, over long spans of time, can probably explain the present occurrences. No pollen production or seed development has been observed in the Svalbard plants we have studied, but see Comments.

Carex lidii differs distinctly from one of its assumed parents, C. parallela, in having a dense cluster of several, bisexual spikes (C. parallela has only one, unisexual spike). It is thereby most similar to C. maritima but differs in much darker spikes with dark brown scales and perigynia, much more narrow spikes (oblong), by more slender leaves and culms and by growing in denser mats. Carex maritima has scales and perigynia yellowish to medium brown, spikes nearly globular, leaves and culms more stout, and growing in rather open mats.

Growing in moist meadows and shallow mires, usually with a rather dense but low-grown vegetation of herbs and mosses. Always in areas with permanent or frequent seepage, from mires upslope or from melting permafrost (percolating water). Carex lidii has only been found on substrates with a basic soil reaction (pH).

Carex lidii is found in the middle and northern arctic tundra zones and the weakly continental and transitional sections. It is documented from five localities or locality groups in Svalbard: on the southern shore of Van Keulenfjorden (Wedel Jarlsberg Land), at Vindodden (the type locality, Nordenskiöld Land) and several places in Sassendalen (Sabine Land) on the south side of Isfjorden, in at least two places at Kapp Wijk at Dicksonfjorden (Dickson Land) on the north side of Isfjorden, and in the inner parts of Edgeøya (a very peculiar site for an assumed hybrid between two moderately thermophilous parents, one of which, C. parallela, never has been recorded from Edgeøya, and the other one, C. maritima, only once and from a different site).

Outside Svalbard, C. lidii is known only from NE Greenland.

Whether C. lidii is a hybrid of the proposed parentage, and whether it reproduces by seeds, are two at present not fully answered questions. Hadač (1944: 24–25) assumed an origin from C. maritima × parallela, and this was the accepted explanation until Øvstedal & Haaland (1996) threw doubts on it. They concluded that it probably was not a hybrid of the assumed parentage but did not propose any alternative explanation. We provisionally accept it as a (probably hybridogeneous) species until its origin is clarified. Both Engelskjøn (in comment in Elven et al. 2011) and Elven still consider the C. maritima × parallela hypothesis the most probable. The morphology suggests the proposed parentage; no feature contradicts this hypothesis.

There is a parallel case in W Greenland and NE Canada, where C. langeana Fernald is proposed to be a hybrid between C. maritima and the western arctic C. gynocrates Wormsk., a relative of C. parallela. H. Solstad & R. Elven (observ.) had the opportunity to study plants of C. langeana in W Greenland in 2013. It had well developed anthers with pollen, and the fruits had started to develop in the middle of August, both features suggesting fertility. We should therefore not assume absolute sterility in C. lidii before it is more thoroughly studied. That is the reason why we here treat it as a species and not just in a comment to one of its assumed parents.

Note that the name Carex lidii Flatberg (Flatberg 1972) is invalid as it is a later homonym and refers to quite another hybrid (C. canescens × chordorrhiza). This name must be rejected.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Flatberg, K.I. 1972. Carex × lidii Flatb. = C. canescens L. × C. chordorrhiza Ehrh. – Norwegian Journal of Botany 19: 91–106.

Hadač, E. 1944. Die Gefässpflanzen des "Sassengebietes" Vestspitsbergen. – Skrifter om Svalbard og Ishavet 87. 72 pp. + XIV Tafel.

Øvstedal, D.O. & Haaland, I.M. 1996. On the origins of Carex × lidii (Cyperaceae) from Spitzbergen. – Symbolae Botanicae Upsaliensis 31(3): 69–74.