Solitary herb with a single root and a more or less extensively branched caudex at the soil surface with leaves in rosettes at ground level. Rosettes are formed the first year, stems the second. Rosette leaves usually wither already in flowering stage the second year. Individual plants vary from very small and stunted (1–2 cm in diameter) to large (15–20 cm or more in diameter), making realistic spans of measurements difficult. One stem from each rosette but often with several flowering branches on the main stem, each with 1–2 (rarely more) leaves. Stems procumbent, spreading or erect. The entire plant glabrous and fresh green.
Leaves alternate. Rosette leaves very variable in size, from 5 mm to 5 cm or more long (the latter found in bird cliff vegetation), with a petiole often 3–4 times as long as the blade, and a blade mostly in the range 8–12 × 6–14 mm, ovate, orbicular or reniform, apex obtuse or rounded. Stem leaves narrower than basal leaves, with shorter petioles, the uppermost often sessile.
Inflorescence a raceme, very short in the flower stage and of very variable size (ca. 0.5–2 × 0.5–3 cm) but initially broader than high, elongating up to 5–10 times in the fruit stage to 3–5 cm or more. Flowers ebracteate except that the lowermost one may occasionally have a bract.
Flowers radially symmetric, 3–6 mm in diameter, with 4 free sepals and petals. Sepals up to 2 × 1.6 mm, very broadly oblong to almost orbicular, green or purple with a broad, white hyaline margin. Petals up to 3–4 × 1.8–2.5 mm, spathulate with a claw about as long as the limb, limb rounded (not notched), white or sometimes pale violet. Stamens 6; filaments ca. 1 mm, flattened; anthers 0.2–0.3 mm. Gynoecium of 2 carpels with 2 rooms separated by a secondary hyaline wall. Style slender cylindrical, very short (0.2–0.3 mm).
Fruit a siliqua, 6–9 × 4–6 mm, thick, subglobular or ovoid, rarely more narrow (extremely variable both in size and shape), with ca. 5 seeds per room. Seeds strongly papillose (probably with floating tissue), ca. 1–1.5 mm, brown.
Sexual reproduction by seeds; no vegetative reproduction. Morphologically adapted to insect pollination but we assume that self pollination prevails. The related C. officinalis L. is characterized by a strong, honey smell (indicating nectar) and is eagerly visited by insects, whereas C. groenlandica has no smell and is rarely visited. Seed production abundant in nearly every years. Seeds germinated to 14 % in an experiment (Alsos et al. 2013), a surprisingly low level of germination for a short-lived solitary herb.
Seeds dispersed by water (downstream and by sea currents due to floating tissue) and probably by wind and birds.
Cochlearia groenlandica may be mistaken for Braya purpurascens, Cardamine bellidifolia, Eutrema edwardsii, or white-flowered Draba spp. Cochlearia differs from Braya in being glabrous and in the rounded shape of the fruit; Braya is hairy in most parts and has broadly sausage-shaped fruits. It differs from Eutrema in being a biennial with numerous basal leaves with broad plates the first year, almost no leaves the second year, and in the short and broad fruits on patent pedicels; Eutrema is perennial with few basal leaves with moderately narrow blades and has narrow and appressed fruits. Cochlearia differs from all Draba in the shape of the fruit, thick and subglobular, and in being glabrous; Draba has comparatively flat or lenticular fruits and almost all white-flowered Draba are hairy.
The range of site types of Cochlearia groenlandica is much larger than in the mainland C. officinalis (even if all its three subspecies are included). It includes all kinds of open, not too dry or too wet ground on gravelly and sandy plains, sediment plains, open patches in moss tundra, frost-patterned ground, along seashores and other shores, and in bird-cliff meadows where it may be the dominant plant and extremely luxuriant. It is indifferent as to soil reaction (pH) and also as to general nutrient level, surviving and reproducing under very harsh conditions as stunted plants but utilizing nutrients in an opportunistic way to become profusely large and reproductive.
This is one of the most widely distributed of all Svalbard plants, common on all major and the majority of smaller islands (the exception being Kvitøya from where almost no vascular plants are known).
It is also widespread at a global scale, arctic circumpolar and present in all major arctic regions.
Elven et al. (2011): "The northern and arctic Cochlearias have been considered either one species (C. officinalis), two or three (in addition C. groenlandica and sometimes C. arctica), or a few times several species. The group has been extensively studied for its ploidy variation in W Europe (e.g., Gill 1965, 1971) and for morphology, ploidy, and physiology in N Europe (Nordal et al. 1986; Nordal & Laane 1990, 1996; Nordal & Stabbetorp 1990; Nordal & Bjorå in prep. Flora Nordica). Justification for the single-species view is found in the essential morphological similarity. Justification for two species is mainly found in two ploidy levels with different base numbers and associated with a few morphological characters (but see the treatment of Nordal & Bjorå). The plants that reach the Arctic are, as far as known, either diploid with 2n = 14 (base number x = 7) or tetraploid with 2n = 24 (base number x = 6). Justification for more than two species is found in some not very significant morphological features. Some revision of this view is under way (Nordal & Bjorå in prep. Flora Nordica).
Löve and Löve (1976) described genus Cochleariopsis to include the taxa with x = 7 (rather than x = 6) but this solution has been accepted by no one else as far as we know. It was quite bold, even for the Löves, to recognize in two genera plants that the majority of researchers rather would consider within a single species.
The tetraploid plant is C. officinalis s. str. It is Atlantic European and reaches the Arctic in Norway and European Russia. Nordal and Bjorå (in prep.) also include the diploid Icelandic plants in this species as a subsp. islandica, probably due to morphological and molecular characters. The species is characterized by relatively large flowers with a honey smell (insect pollinated and outcrossing), by mainly being biennial (except for subsp. integrifolia), and by some small features in leaf and fruit shape. The other northern diploid plants are sometimes divided on two species: the circumpolar C. groenlandica (type from Greenland) and the N Eurasian and amphi-Pacific/Beringian C. arctica (described from NW Siberia). Both are largely similar to C. officinalis in morphology and molecular markers. The different base numbers may be due to aneuploidy associated with the polyploidization.
Cochlearia groenlandica differs from the European Atlantic tetraploid C. officinalis s. str. (and probably also from the Icelandic diploid) mainly in being potentially perennial and in having much smaller flowers without the distinct honey smell of C. officinalis, i.e., both the latter characters associated with predominant inbreeding. There may be some chemical (glycosides) and physiological differences (Nordal in comment). As the arctic diploid and the NW European diploid + tetraploid probably are reproductively isolated and differ morphologically and ecologically, they can be justified as different species at least from a 'biological' point of view. They have nearly allopatric ranges, possibly with a small overlap in N Russia. ... All plants inspected from Svalbard and Greenland, and all northern arctic plants from North America and Russia–Siberia, conform morphologically to C. groenlandica (as to type). This means that the names C. fenestrata (based on a plant from arctic NE Canada) and C. polaris (based on a plant from Franz Joseph Land) are synonyms for C. groenlandica."
Previous treatments of the Svalbard flora (e.g., Rønning 1964, 1979) have sometimes accepted three species – C. anglica, C. arctica and C. officinalis – but almost never C. groenlandica. Note that the northernmost occurrences of C. anglica accepted today are in Denmark and southernmost Sweden and as recently established on the Lista peninsula in southernmost Norway. The assignment of specimens according to this view has been almost entirely by size. Our current opinion is that all Svalbard plants belong to a polymorphic and very plastic C. groenlandica.
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) Vascular plants. http://panarcticflora.org/
Gill, J.J.B. 1965. Diploids in the genus Cochlearia. – Watsonia 6: 188–189.
Gill, J.J.B. 1971. Cytogenetic studies in Cochlearia L. – Annals of Botany (London) 35: 947–956.
Löve, Á. & Löve, D. 1976. Nomenclatural notes on arctic plants. – Botaniska Notiser 128: 497–523.
Nordal, I., Eriksen, A.B., Laane, M.M. & Solberg, Y. 1986. Biogeographic and biosystematic studies in the genus Cochlearia in Northern Scandinavia. – Symbolae Botanicae Upsaliensis 27(2): 83–93.
Nordal, I. & Laane, M.M. 1990. Cytology and reproduction in Arctic Cochlearia. – Sommerfeltia 11: 147–158.
Nordal, I. & Laane, M.M. 1996. Taxonomic delimitation within Cochlearia officinalis s. lat. with particular discussion on the rank of C. anglica (Brassicaceae). – Symbolae Botanicae Upsaliensis 31(3): 47–57.
Nordal, I. & Stabbetorp, O.E. 1990. Morphology and taxonomy of the genus Cochlearia (Brassicaceae) in Northern Scandinavia. – Nordic Journal of Botany 10: 249–263.
Rønning, O.I. 1964. Svalbards flora. – Norsk Polarinstitutt, Oslo.
Rønning, O.I. 1979. Svalbards flora. Ed. 2. – Norsk Polarinstitutt, Oslo.