Panarctic Flora

6722 Cochlearia L.

• L., Sp. Pl.: 647 (1753).
• Cochleariopsis Á. Löve & D. Löve, Bot. Not. 128: 513 (1976).

Notes: 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 western Europe (e.g., Gill 1965, 1971) and for morphology, ploidy, and physiology in northern Europe (Nordal et al. 1986; Nordal and Laane 1990, 1996; Nordal and Stabbetorp 1990; Nordal and 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 and 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 impressive morphological features. Some revision of this view is under way (Nordal and Bjorå in prep. Flora Nordica).

Löve and Löve (1976a) 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 northern Eurasian and amphi-Pacific/Beringian C. arctica (described from northwestern 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 northwestern 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 northern Russia.

There are more doubts about whether the arctic diploids can be divided on two species. The formal morphological distinctions between C. arctica and C. groenlandica are small but the characters reported (Petrovsky 1975c; Nikiforova 1994; Sergienko 2008) distinguish between plants that may be recognizable in the field and which have different (albeit strongly overlapping) ranges. 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 an arctic northeastern Canadian plant) and C. polaris (based on a Franz Joseph Land plant) are synonyms for C. groenlandica. The more southern arctic plants in northern mainland Russia-Siberia, the Russian Far East, and in Beringian Alaska differ in being more erect with regular branching of the stems and more stem leaves, perhaps also in fruit shape. They have traditionally been assigned under the name C. arctica and are reluctantly accepted by us as a third species. This acceptance is not shared by Nordal in her extensive study of North Atlantic variation in Cochlearia but she did not study much material from northern Russia and Siberia or Beringia. In comparative cultivation, C. groenlandica from Svalbard and C. arctica (subsp. oblongifolia) from Alaska retain or even strengthen their morphological differences but are fully interfertile (L. Gustafsson unpubl.).