Solitary herb with caudex, usually with several erect to ascending branches, each ending in a rosette at ground level, mostly several rosettes together in a dense or loose tussock. Each rosette potentially with one leafy flowering stem. Stems 6–12(15) cm, erect, glabrous. A majority of plants in Svalbard are observed with rosettes only, often difficult to see in the deep wet moss carpets where it grows.

Leaves alternate, glabrous. Rosette leaves to 6(10) cm, pinnate with a long petiole about 1/2 the total leaf length; the blade 2–4(5) × 0.5–1.5 cm with a linear to narrowly oblong outline. Rosette leaves have leaflets in 3–6(8) pairs but several leaflets are usually shed early in season (see Reproduction). Each leaflet (2)3–5 × (1)2–4 mm, sessile or short petiolulate, oblong, slightly fleshy with upturned margins (shaped like a spoon or an obtuse dinghy), veins indistinct and usually impressed. Stem leaves 3–5, similar to rosette leaves but with more narrow leaflets that usually are not shed early in the season.

Inflorescence a raceme, short at flowering time 1–1.5(2) × 3–3.5(4) cm (i.e., much broader than long), with all flowers at the same height due to longer pedicels (4–8 mm) on the lower flowers, with 5–15 flowers on pedicels diverging at 45–60° from stem. Inflorescence elongating in fruit stage.

Flowers radially symmetric with 4 free sepals and petals (crucifer flowers). Sepals 3–7 × 2–4.5 mm, ovate, apex obtuse to rounded, green or pink with broad, white hyaline margins. Petals 6–10 × 4–6 mm, cordate or spathulate with narrow claw about 1/4 of the petal length and a broad, sometimes slightly notched limb, white or pink. Stamens 6, yellow. Pollen well developed in many inspected plants (see Reproduction). Gynoecium of 2 carpels with 2 rooms separated by a secondary, hyaline wall.

Fruit a long, narrow siliqua with numerous seeds along the suture between the carpels. Mature fruits not observed in Svalbard material, also rare elsewhere.

Reproduction by seeds, probably not realized in Svalbard; efficient vegetative reproduction by leaflets. The main means of reproduction is by detached leaflets, and this may be the only means in Svalbard. The leaflets loosen very easily from the midrib of the leaf and sometimes only the midribs are left of the entire rosette at the end of the season. There may be occasional seed reproduction (anther and pollen often well developed) but this means of reproduction plays a minor part in sustaining populations and also in long-range dispersal. Reported chromosome numbers are high and irregular (2n = ca. 56–ca. 100, i.e., 7-ploid to ca. 12-ploid as the basic number is × = 8) and may cause disturbances in the meiosis, the probable reason for the usually failing seed-set. Both the two other North European species of the C. pratensis complex – C. pratensis L. s. str. and C. dentata Schult. – have similar high and irregular chromosome numbers and no or only intermittent seed-set.

The leaflets, which function as small bulbils, are dispersed by water and probably to a very large extent by birds foraging in wetlands.

The pinnate leaves of Cardamine nymanii has only one parallel in the Svalbard flora, those of Polemonium boreale (note the Cardamine synonyms with ‘polemonioides’), but this is the only characters these two have in common. Polemonium is densely hairy, with large, blue flowers with fused petals (sympetalous), and grows in dry sites. When in flower, C. nymanii is evidently a crucifer but no other Svalbard crucifers have pinnate leaves or large, usually pink flowers.

Cardamine nymanii is restricted to very moist, wet or submerged sites where it usually grows in dense moss carpets, sometimes alone on wet or irrigated gravel or sand. It is indifferent as to soil reaction (pH).

Present in all zones and sections but more sparsely and not flowering in the polar desert zone. Probably common all over the major islands of Svalbard from Bjørnøya northeast to Nordaustlandet but not (yet) recorded from Hopen or Kong Karls Land. The species is easily overlooked when growing without flowering stems in deep moss carpets. The absence in some parts (see the map) is probably due to the species being overlooked rather than being absent.

This is a very widespread plant throughout the arctic circumpolar areas and also reaching south in many mountains, in Europe south to S Norway.

The Cardamine pratensis group is unusually complicated taxonomically. It consists of several diploid and tetraploid species in S and C Europe and a superstructure of the three highly polyploid species mentioned above, of which C. pratensis s. str. is mainly European, C. dentata European and probably NW Asian, and C. nymanii is circumpolar (and the only native member of the group in Greenland, North America, and E Asia). This group of three high polyploids is a distinct clade with a European origin (Carlsen et al. 2009), well separated from all other parts of the genus. They have been considered three subspecies (see, e.g., Jones & Marhold 1993; Elven in Lid & Lid 2005) but there is extensive sympatry (overlap of ranges), little sign of any transitions, and no good reason for considering them anything but species, except that they share many characters. Accordingly, Elven et al. (2022) assigned them rank as separate species. Cardamine nymanii is distinguished by, e.g., the glabrous, entire, fleshy leaflets with impressed veins. In the two others, the leaflets are often hairy, dentate, thin, and with protruding veins. Cardamine nymanii is distinguished from C. pratensis also by the often distinct petiolules of leaflets on stem leaves (in common with C. dentata but absent from C. pratensis).

There is a plethora of names for this taxon, some of them not yet confirmed by types. The two unambiguous names are C. nymanii Gand. 1926, based on a type in P (the Paris herbarium) from Ny-Ålesund in Spitsbergen, and C. pratensis ssp. angustifolia O.E.Schulz 1903, based on a type from Southampton Island at the entrance to Hudson Bay in Canada. The older name C. polemonioides Rouy 1893 was coined to include plants from Svalbard, Novaya Zemlya and Iceland. It is probable that the author intended to describe our plant, but as plants from Iceland may belong to other races, a designation of an exact type specimen from a specified location is needed before this name can be (re)instated as a priority species name. As for subspecific names, we can find no valid primary publication of the combination C. pratensis ssp. polemonioides applied by, e.g., Flora Europaea (Jones & Marhold 1993). Rouy published it as a species name only. This means that C. pratensis ssp. angustifolia is the correct name for a subspecies if North American and European plants are the same. Just this question was raised by V.V. Petrovsky (in Elven et al. 2011). He commented that Hooker's and Schulz' var. or ssp. angustifolia only could be synonymized with Rouy's ssp. polemonioides (and Gandoger's C. nymanii) if the Hooker plant was from Europe. He thereby implied that the American and European plants were different at level of species or subspecies. We have compared American, Greenland and European plants and find no difference of any importance. Note also that the entire C. pratensis group otherwise is European. The American plants must have arrived from Europe and perhaps within the last 10,000 years.

Hooker (1828) reported the western arctic Parrya nudicaulis (L.) Regel from Heclahamna at Sorgfjorden (Ny-Friesland) on Spitsbergen, based on a Parry collection from 1827. If there ever was a voucher specimen it must have been deposited in London (BM, Natural History Museum) but no one has seen it in recent times. Elven & Elvebakk (1996) suggested that it could be a misinterpretation of Arabis alpina; however, that is rather far-fetched as Arabis is western and oceanic and not known from Sorgfjorden or any nearby area. The most probable interpretation is that the large, pink flowers of Cardamine nymanii were mistaken by Parry for the also large-flowered and pink Parrya nudicaulis (a species he knew under a different name from arctic Canada). Incidentally, the genus Parrya is named in honour of just this Captain Parry who collected the species that later was named as Parrya arctica on Melville Island in arctic Canada during one of the many early attempts to find the Northwest Passage. The Parry arctic expeditions were among the more successful from a botanical and human point of view; a lot of important plants and other samples were collected, and no participant died.

Carlsen, T., Bleeker, W., Hurka, H., Elven, R. & Brochmann, C. 2009. Biogeography and phylogeny of Cardamine (Brassicaceae). – Annals of the Missouri Botanical Garden 96: 215–236.

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

Elven, R. & Elvebakk, A. 1996. Part 1. Vascular plants. – In: Elvebakk, A. & Prestrud, P. (eds.), A catalogue of Svalbard plants, fungi, algae, and cyanobacteria. – Norsk Polarinstitutts Skrifter 198: 9–55.

Hooker, W.J. 1828. Botanical appendix to Parry, W.E., Narrative of an Attempt to reach the North Pole. – London.

Jones, B.M.G. & Marhold, K. 1993. Cardamine L. p.p. – In: Tutin, T.G. et al. (eds.), Flora Europaea. 1. Psilotaceae to Platanaceae. Ed. 2: 348–350.

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