Solitary to weakly mat-forming herb with a central root, a caudex extensively branching at ground level, and possibly with rooting branches. A large number of shortened vegetative shoots constitute small tussocks or more extended open mats in moss carpets. Old leaves are not retained. Lateral shoots in upper leaf axils and shoot tips develop into pale green bulbils easily detached from and dispersing the plant. Flowering stems (rare in Svalbard) up to 3 cm.

Leaves opposite, 3–6 mm, linear, without distinct sheaths, lamina with indistinct mid vein (i.e., ‘one-veined’), on extended shoots diverging at broad angles (ca. 90º), on shortened shoots incurved, not retained past the season, obtuse, mostly purplish green.

Flowering shoots (when present) with a single terminal flower on pedicel up to 20 mm.

Flowers radially symmetric with 5 free sepals and petals. Sepals 1.5–2.5 × 0.7–1.0 mm, oblong or ovate, obtuse or subacute, with one indistinct vein, purple. Petals as long as sepals, obovate, rounded at apex, white. Stamens 10. Gynoecium of 3 carpels with 3 stigmas.

Fruit a one-roomed capsule that opens apically with 3 teeth, but rarely developed in Svalbard. Mature seeds not observed.

Vegetative reproduction by fragmentation of mats but especially by bulbils. Bulbils may be the only efficient mode of reproduction for the species in Svalbard (and also elsewhere). Flowers small and probably not adapted to insect pollination; self pollination assumed to prevail. Flowering only intermittently in Svalbard and not recorded with fruit. However, Alsos et al. (2013) reported seed germination of 33 % in an experiment. The voucher plant for the seeds has been inspected but a mistake in identity is nevertheless suspected.

Bulbils are easily detached and transported by water, birds and perhaps wind. No special adaptations to seed dispersal (if any takes place at all).

The species of Minuartia can be confused with those of Sagina but differ in having 3 styles and capsule teeth, whereas Sagina has 4–5 styles and capsule teeth. This is not always easily observed, but the shapes of buds, sepals and capsules are usually different. Whereas Sagina has nearly globular buds, short and boat-shaped sepals, and ovoid capsules, Minuartia has elongated buds, lanceolate sepals, and usually more elongated capsules. However, among the Svalbard species of Minuartia and Sagina, M. rossii is the only one with bulbils and mostly easily recognized.

Within Minuartia, M. rossii can be confused with M. stricta only. The main difference is that M. rossii usually reproduces with bulbils formed as apices of vegetative shoots, whereas such bulbils never are found in M. stricta. However, there are populations of M. rossii, in Svalbard and elsewhere, that flower and do not produce much bulbils. These plants are difficult to keep apart from M. stricta (and have resulted in numerous misidentifications). Lid noted on a herbarium sheet in 1969 the following useful character: "M. rossii has more obtuse sepals, less marked sepal veins, and sepals not above 2.2 mm, and in addition very short internodes." [Translated here from Norwegian.]

Moist or wet plains and gentle slopes with little or no vegetation, with a permanently high water table, continuous seepage from melting permafrost or snowbanks or at least temporarily wet, growing either directly on the substrate or intermingled with mosses. The substrate varies from very fine (clay) to mixed fine/coarse (sand/gravel), but always with a high water retention capacity. Mostly found on basic substrates and becoming rare already on circumneutral substrates.

Cryophilous. Present in the middle and northern arctic tundra zone, in some places touching on the polar desert zone (Sorgfjorden, Wahlenbergfjorden); present in all sections. Restricted to Spitsbergen and one documented site at Zeipelodden on Nordaustlandet (Wahlenbergfjorden, Gustav Adolf Land), and also restricted to the areas with calcareous substrates, mainly north of Isfjorden.

The global range lies entirely within the Arctic. Minuartia rossii is mainly North American, transgressing in the east across N Greenland to Svalbard, in the west across the Bering Strait to E Chukotka and Wrangel Island in the Russian Far East (the only Asian regions for this species). The connections of the Svalbard plants are therefore obviously to the west (Greenland and Canada).

Minuartia rossii is closely related to the Beringian M. elegans (Cham. & Schltdl.) Schischk., and these two constitute a group distinct from all other Minuartia. Minuartia elegans differs from M. rossii mainly in that it flowers and fruits regularly and that it does not produce bulbils. One could suspect that this difference was due to environment, as the seed-reproducing M. elegans is a more southern species, boreal and low arctic, than the bulbil-reproducing, high arctic M. rossii. However, their differences are retained when cultivated in a phytotrone (University of Oslo). Wolf et al. (1979) found good morphological support for accepting two species, partly differing also in ploidy levels: M. elegans is diploid and probably tetraploid with 2n = 30 and 60; M. rossii is uniformly tetraploid with 2n = 60 (Elven et al. 2011). Wolf et al. (1979) interpreted tetraploid M. elegans to be an autotetraploid, which might imply that M. rossii could be an allotetraploid with one diploid genome from M. elegans and one from another species. Minuartia stricta comes to mind.

The genus Minuartia is heterogeneous and polyphyletic (Nepokroeff et al. 2001, 2002) and will in the future probably fall apart into several genera. The Svalbard plants may then be assigned to the genera Tryphane (rubella), Lidia (biflora), and Alsinanthe (rossii and stricta). This also means that, whereas M. rossii and M. stricta are fairly closely related, these two and the two others are only distantly related.

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.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).

Nepokroeff, M. et al. 2001. Origin of the Hawaiian subfam. Alsinoideae and preliminary relationships in Caryophyllaceae inferred from matK and trnL–C–F sequence data. – In: Botanical Society of America. 2001. Botany 2001 Abstracts: 130.

Nepokroeff, M. et al. 2002. Relationships within Caryophyllaceae inferred from molecular sequence data. – In: Botanical Society of America. 2002. Botany 2002 Abstracts: 105.

Wolf, S.J., Packer, J.G. & Denford, K.E. 1979. The taxonomy of Minuartia rossii (Caryophyllaceae). – Canadian Journal of Botany 57: 1675–1686.