Solitary or weakly mat-forming herb with short subterranean runners, extensively branched at ground level, laxly caespitose or forming small stands. Flowering stems 3–10(15) cm.
Leaves alternate. Basal leaves 5–20 mm, entire, lanceolate or narrowly lanceolate, obtuse, with a long sheathing petiole, sparsely to moderately pubescent with long, reddish brown hairs, especially in basal parts. Stem leaves 4–8, smaller than the basal ones and mainly on the lower parts of the stem.
Flowers terminal on stem, singly or more rarely 2–3 in a cyme.
Flowers radially symmetric with 5 free sepals and petals. Sepals 3–6 × 1–3 mm, spreading at anthesis, deflexed in fruit stage, narrowly oblong or lanceolate, dark red. Petals 10–15 × 4.5–7 mm, oblong, obtuse and often slightly notched, not overlapping, yellow and often with reddish dots. Ovary semi-inferior, of two carpels with two rooms, split apically.
Fruit a capsule with numerous seeds.
Sexual reproduction by seeds; very local vegetative reproduction by fragmentation of rhizome, forming small colonies. Flowering regularly but comparatively late in the season. Flowers adapted to insect pollination. Assumedly with regular seed set, but the seeds seem mainly unripe and their germination percentage is <5 % (Alsos et al. 2013; Müller et al. 2011).
Capsules have apical opening which ensures that the seeds only are dispersed out at a minimum 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 dispersal by animals, e.g. geese that selectively feed on seed capsules (Prop et al. 1984).
The three yellow-flowered Saxifragas of Svalbard are rather different. Saxifraga platysepala is distinguished from the two others by its long, above-ground runners (stolons) ending in small rosettes (the "Spider Saxifrage") and by being glandular pubescent. Saxifraga aizoides and S. hirculus are distinguished by the former having ciliate leaves, small and often several flowers per stem, and by sepals appressed or patent in late flower and fruit stages; the latter having entire leaves, large and mostly single flowers, and by sepals deflexed in late flower and fruit stages.
Most common in moss tundra and other moist tundras with dense vegetation. Also recorded from soil banks and rarely from shallow mires. On fine textured or mixed substrates with impeded or moderate drainage, and weakly acidic to basic soil reaction (pH). Probably requiring good protection from snow during winter but not adapted to short growing seasons as in snowbeds. Little grazed by reindeer and geese.
Not present in the harshest environments in Svalbard. Frequent in the middle and northern arctic tundra zones, barely transgressing into the polar desert zone. Present in all sections, but very rare in the clearly continental section. Present on all major islands and rather frequent in parts of Spitsbergen.
The general range of the species Saxifraga hirculus is circumpolar in the arctic, boreal and northern temperate zones and in mountains. The Svalbard ssp. compacta is distributed in Svalbard, E Greenland, Iceland (probably), N Norway (one stand discovered in 2013, eradicated in 2014, see Solstad et al. (2021) and Elven et al. (2022), and arctic Russia and Siberia. For the ranges of the other proposed races, see Comments.
Saxifraga hirculus is very polymorphic and several geographical races have been proposed. The main plant in temperate and boreal regions, in both Eurasia and North America, is the tetraploid (2n = 32) ssp. hirculus, tall-grown and with extensive stolons, forming very loose carpets in wet mires. Löve (1970) assigned the plants of Svalbard and Iceland to ssp. alpina (Engl.) Á.Löve but this is an evident misapplication by Löve of Engler's name based on a plant from the Himalayas (see Webb & Gornall 1989). Hedberg (1992), in a revision of this group, assigned the plants in the North Atlantic, European and Siberian Arctic to a tetraploid (2n = 32) ssp. compacta, described on a type from Svalbard, whereas those in the American Arctic mainly were assigned to the diploid (2n = 16) ssp. propinqua, based on a plant from Melville Island in the Canadian Arctic. Hedberg's revision is supported by differences in morphological features and in ploidy levels but has not been generally accepted. In the single molecular study known to us (Oliver et al. 2006), geographical entities (races) were not well supported. The only population from Svalbard analysed by Oliver (2006) showed two haplotypes unique to Svalbard, but their relations to populations from other geographical regions are not obvious.
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., Bjorå, C.S., Fremstad, E., Hegre, H. & Solstad, H. 2022. Norsk flora. Ed. 8. – Det Norske Samlaget, Oslo.
Hedberg, O. 1992. Taxonomic differentiation in Saxifraga hirculus L. (Saxifragaceae) – a circumpolar arctic–boreal species of Central Asiatic origin. – Botanical Journal of the Linnaean Society 109: 377–393.
Löve, Á. 1970. Emendations in the Icelandic flora. – Taxon 19: 298–302.
Müller, E., Cooper, E.J. & Alsos, I.G. 2011. Germinability of arctic plants is high in perceived optimal conditions but low in the field. – Botany 89: 337–348.
Oliver, C., Hollingsworth, P.M. & Gornall, R.J. 2006. Chloroplast DNA phylogeography of the arctic-montane species Saxifraga hirculus (Saxifragaceae). – Heredity 96: 222–231.
Solstad, H., Elven, R., Arnesen, G., Eidesen, P.B., Gaarder, G., Hegre, H., Høitomt, T., Mjelde, M. & Pedersen, O. 2021. Karplanter: Vurdering av polarmyrsildre Saxifraga hirculus subsp. compacta for Norge. Rødlista for arter 2021. Artsdatabanken. https://www.artsdatabanken.no/lister/rodlisteforarter/2021/2048
Webb, D.A. & Gornall, R.J. 1989. A manual of Saxifrages and their cultivation. – Timber Press, Portland, Oregon.