Life span

Perennial, probably not very long-lived.

Growth form

Solitary herb with a very short, subterranean caudex, simple or with short vertical branches, each ending in a leaf rosette at ground level. Flowering stems (scapes) erect, (4)5–15(20) cm, singly from rosettes, 1–2(2.5) mm thick, pubescent with long and curly/intertangled, articulate hairs, often as long as or longer than the stem diameter. Hairs white with white cell walls but often with purple gland tips.

Leaf

Leaves alternate, all basal in rosettes, 3–4 × 1.5–2 cm, with blades broadly ovate to rounded with rounded apex, coarsely dentate with obtuse triangular teeth as broad as or broader than wide, blade narrowing more or less abruptly to a short, winged petiole. Sometimes with a single, narrowly ovate, entire stem leaf. Sparsely pubescent with articulate hairs.

Inflorescence

Inflorescence of 1–5 (or more) clusters, each with 1–4 (or more) flowers in a short, often capitate panicle. Bracts below each inflorescence branch entire, narrowly ovate.

Flower

Flowers radially symmetric with 5 free sepals and petals. Sepals 1.3–2.3 × 1.3–2.3 mm, broadly ovate to triangular, obtuse, appressed to patent, green to reddish. Petals 2.5–3.2 × 1.0–1.3 mm, 1.5–2 times as long as sepals, narrowly oblong, obtuse to rounded, non-overlapping, white or more rarely pale pink. Stamens 10. Gynoecium semi-inferior, of two carpels, split apically and with 2 stigmas.

Fruit

Fruit a capsule with two beaks bending up to 90° outwards when ripe. Seeds numerous.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. The flowers are small and little visible and self-pollination is assumed to be the main mode in Svalbard. The plant flowers and fruits regularly and ripe seeds are assumed to be produced regularly. Seeds germinate to > 60 % (Alsos et al. 2013). Abundant seeds germinate from seed bank (Cooper et al. 2004).

Capsules have apical opening which ensures that the seeds only are dispersed at a certain wind speed. Seed dispersal is often after the first snow fall, which increases the dispersal distance as the seeds are blown across a smooth surface (Savile 1972). Seeds are also dispersed by animals, e.g. geese, that selectively feed on capsules (Prop et al. 1984).

Comparison

Micranthes nivalis may superficially be similar to M. tenuis but the two differ in several characters: Micranthes nivalis has comparatively stout scapes that are distinctly pubescent with hairs > 1 mm long, the scape hairs are curly, white and only purple at the very tip, the rosette leaves are more rhombic with narrower teeth pointing somewhat forwards, the inflorescence is more compact with several densely clustered flowers per branch, and the beaks of the capsule bend out but not back (up to 90°); M. tenuis has more slender scapes which appears almost glabrous when seen without a hand lens, i.e., with sparse hairs < 1 mm long, the scape hairs are purple, also the cell walls, and less curly, rosette leaves are rounded with broad teeth pointing outwards, the inflorescence is more open and has branches with single flowers, and the beaks of the capsule bend back (more than to 90°).

Tall-grown Micranthes nivalis is sometimes mistaken for M. hieraciifolia (or for the not confirmed hybrid M. hieraciifolia × nivalis). Micranthes hieraciifolia differs from M. nivalis in numerous features, foremost the very small and deep red petals and the broadly triangular sepals, but also leaf shape, the very stout scapes, and the elongated, interrupted inflorescence with several clusters of purple flowers.

Of the four species of Micranthes in Svalbard, M. foliolosa and M. hieraciifolia are easily separable from the two others and from each other even by their leaves. Micranthes foliolosa has characteristic, obovate or obcuneate leaves with a few triangular teeth in the distal 1/3 only, and the leaves are thin and glabrous; M. hieraciifolia has ovate or lanceolate, subacute or acute leaves with sparse, shallow teeth along the sides, and the leaves are thick and with white, articulate hairs along the margins and on the lower surface. Micranthes nivalis and tenuis both have thick, rounded leaves with obtuse, forward pointing teeth, and they are not easily separable on their leaves alone. However, whereas M. nivalis has a fair amount of white and often some brown hairs along the leaf margins and on the lower surface, M. tenuis has only a scattering of very dark brown hairs on the lower surface.

Habitat

Heaths, herb slopes, screes, dry river terraces, and similar sites. Predominantly on well-drained coarse substrates (sand, gravel, stones). Micranthes nivalis is a specialist of dry heaths, as opposed to M. tenuis which rather is a specialist of moist snowbeds. Largely indifferent as to soil reaction (pH).

Distribution

Frequent in all zones and sections. Found on all major islands in the Spitsbergen group and on Bjørnøya.

The general range is circumpolar and arctic–alpine; the species is very widespread.

Comments

The group of Micranthes nivalis, M. tenuis, and two relatives (the Americans M. rufopilosa (Hultén) D.F.Murray & Elven and M. gaspensis (Fernald) Small, see Murray & Elven in print) has not been fully investigated as to molecular variation, but the two species present in Svalbard have been studied in Canada (Healy & Gillespie 2004). Morphologically, the two keep distinct, even when growing in close vicinity (Elven et al. 2011). Whereas M. tenuis is a diploid (2n = 20), M. nivalis is a hexaploid (2n = 60), and there is only a single substantiated report of a tetraploid (from Yukon, Canada). Until recently (after 2000), the majority of North American authors did not accept M. tenuis and M. nivalis as different, whereas these two have been accepted as independent species in N Europe for at least the last 60–80 years. Hybrids have been proposed now and then but never confirmed. The current evidence is that they are two well different species, often co-occurring in areas (but rarely within sites due to the different ecological demands), but never or very rarely forming any transitional forms.

Literature

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.

Cooper, E.J., Alsos, I.G., Hagen, D., Smith, F.M., Coulson, S.J. & Hodkinson, I.D. 2004. Recruitment in the Arctic: diversity and importance of the seed bank. – Journal of Vegetation Science 15: 115–124.

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

Healy, C. & Gillespie, L.J. 2004. A systematic analysis of the alpine saxifrage complex (Saxifragaceae) in the Canadian Arctic Islands using morphology and chloroplast DNA data. – Canadian Field-Naturalist 118: 326–340.

Murray, D.F. & Elven, R. In print (2015). Micranthes rufopilosa (Hultén) comb. nov.: an alpine species from Alaska and Yukon. – Journal of the Botanical Research Institute of Texas.

Prop, J., van Erden, M.R. & Drent, R.H. 1984. Reproductive success of Barnacle Goose Branta leucopsis in relation to food exploitation on the breeding grounds, western Spitsbergen. – Norsk Polarinstitutts Skrifter 181: 87–117.

Savile, D.B.O. 1972. Arctic adaptations in plants. – Canada Department of Agriculture Research Branch Monograph 6. 81 pp.