Solitary herb growing in small tussocks from a short, branched rhizome. Most leaves are basal. Culms 2–6(7) cm, erect, terete, smooth or slightly ridged, without or with one leaf on the lower half of the culm.

Leaves 1.5–4 cm, as long as or slightly shorter than culms, thin, 0.5–0.9 mm, filiform and canaliculate, smooth or slightly ribbed, with a 0.5–1.5 cm long, reddish brown sheath with distinct, rounded auricles at the transition to the blade.

Inflorescence a head with (2)3(5) flowers at the same height or one of the flowers slightly (1–2 mm) below the others, subtended by usually 3 bracts. Bracts 2.5–3.5(5) mm, broadly lanceolate or ovate, acute, reddish brown with a dark brown mid vein running into the apex. Bracts shorter than flowers or sometimes the mid vein of the lowermost bract continues as an up to 14 mm subulate tip beyond the flowers. The entire inflorescence turns greyish white with age, a character visible on most plants as the culms and inflorescences often remain on the plant for several years.

Flowers radially symmetric. Perianth of 6 (3 + 3) tepals. Tepals lanceolate. Outer tepals 3–4 mm, acute, brownish red or pinkish; inner tepals slightly shorter than the outer ones, obtuse, whitish and much more hyaline, as long as fruit. Stamens 6, as long as tepals; anthers narrow, 0.6–0.8(0.9) mm long. Gynoecium of 3 carpels with 3 stigmas.

Fruit a one-roomed capsule, 3–4(5) mm, acute, with an up to 1 mm cylindrical style, shiny, olive brown, with numerous seeds.

Sexual reproduction by seeds; no vegetative reproduction. Adapted to wind pollination (protogyny, i.e., stigmas predate stamens) but self pollination is assumed to be common. Seed production is regular in Svalbard. Seeds germinated to ca. 90 % in an experiment (Alsos et al. 2013).

The seeds are passively spread but more long distance dispersal with birds, often frequenting the marshes where the species grows, is probable.

Juncus albescens has all flowers in a small cluster and can only be mistaken for J. biglumis. They differ markedly in position of flowers and shape of fruits: J. albescens has its usually three flowers at the same level and an acute capsule; J. biglumis has its usually two flowers at different levels and a truncate or emarginate capsule with the style as an apical, narrow beak in a depression at top of the capsule. The inflorescence of J. biglumis remains black with age, whereas that of J. albescens turns whitish.

For differences between J. albescens and the closely related, more southern J. triglumis (the species of the Fennoscandian mainland), see Comments.

Juncus albescens is a specialist of shallow, arctic mires, almost never found in any other environment. It grows in mires on fairly basic substrates, always wet and never in a dense, tall-grown sward that could outcompete it.

Thermophilous. In the middle arctic tundra zone and the weakly and clearly continental sections. This species is restricted to NC Spitsbergen, never found on any other island in Svalbard. It is confined to the areas surrounding the middle and inner parts of Isfjorden, Kongsfjorden and Wijdefjorden.

The range of Juncus albescens is uncertain but probably nearly circumpolar in the southern arctic and the northern boreal zones. This is the main species in the American Arctic (Greenland, Canada, Alaska) and most probably also penetrating into NE Asia in the Russian Far East and perhaps Siberia. It seems to be absent from European Russia (Elven et al. 2011). Hence, the connection of the Svalbard plants is most likely to the west.

The two taxa within Juncus triglumis s. lat. have been treated as species (e.g., Porsild & Cody 1980; Elven et al. 2022), subspecies (e.g., Tolmachev 1963; Hultén 1968; Elven in Lid & Lid 1994, 2005; Cody 1996; Kirschner et al. 2002), or varieties (e.g., Brooks & Clemants 2000). Some authors report J. triglumis and J. albescens to be largely sympatric and difficult to keep apart in several regions (e.g., Kirschner et al. 2002), whereas others report comparatively clear-cut morphological differences (e.g., Brooks & Clemants 2000). Main differences are: In J. triglumis the longest subtending bract is short and obtuse, the tepals are short and obtuse and about half the length of the mature capsule, not turning whitish in withering, the fruit is tapering beneath the beak, and the culms much longer than leaves; in J. albescens the longest subtending bract is longer, acute or with an extended subulate plate, the tepals are longer, more acute and at about the same length as the capsule, turning whitish on withering, the fruit is tapering at the very beak, and the culms are about as long as leaves. In Scandinavia, J. triglumis s. lat. is the taller plant, J. biglumis the smaller plants, in Svalbard the opposite. This is a paradox for the Scandinavian botanists travelling to Svalbard for the first time and seeing those two species: The reason is not only that J. biglumis often is taller and more luxuriant in Svalbard than in Scandinavia, it is also because the Svalbard J. albescens is a much smaller plant than its Scandinavian relative J. triglumis.

Comparing plants from mainland Europe (J. triglumis s. str.) with ones from Svalbard, Greenland and E Canada (J. albescens), the differences cited above hold nicely, but not as well when comparing with plants from NW North America and NE Asia where the variation may be less discontinuous. However, we have seen no plants closely approaching mainland European J. triglumis morphologically from these other arctic regions. The variation within J. albescens may be larger than presumed from a study of North Atlantic and E North American specimens alone. We are not convinced that the sympatry is as extensive as proposed by, e.g., Kirschner et al. (2002). Our reason for choice of species rank is that we have not seen any transitional forms in the few areas where the two occur close together (parapatric) or in contact (sympatric).

Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.

Brooks, R.E. & Clemants, S.E. 2000. Juncus Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae: 211–255.

Cody, W.J. 1996. Flora of the Yukon Territory. – NCR Research Press, Ottawa.

Elven, R., Bjorå, C.S., Fremstad, E., Hegre, H. & Solstad, H. 2022. Norsk flora. 8. Ed. – Det Norske Samlaget, Oslo.

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

Hultén, E. 1968. Flora of Alaska and neighboring territories. A manual of the vascular plants. – Stanford Univ. Press, Stanford.

Kirschner, J. et al. 2002. Species plantarum: flora of the world. Part 7. Juncaceae: Juncus subg. Juncus. – Australian Biological Resources Study, Canberra.

Lid, J. & Lid, D.T. 1994. Norsk Flora. Ed. 6 by R. Elven. – Det Norske Samlaget, Oslo.

Lid, J. & Lid, D.T. 2005. Norsk Flora. Ed. 7 by R. Elven. – Det Norske Samlaget, Oslo.

Tolmachev, A.I. 1963. Flora Arctica URSS. IV. Lemnaceae–Orchidaceae. – Akademiya Nauk SSSR, Moskva–Leningrad.