Panarctic Flora

672131 Draba rupestris W.T. Aiton

• W.T. Aiton, Hort. Kew., ed. 2, 4: 91 (1812). Described from Scotland.
• Draba norvegica auct., non Gunnerus (1776). See notes below and to Draba glabella.

2n= 48 (6x). - Europe (N), Canada (E), Greenland. - Numerous reports.
Not included: A report of 2n = 48 from the Northwest Territories (Mulligan and Cody 1968, as D. norvegica). The species needs confirmation from this western region.

Geography: Amphi-Atlantic: ICE NOR RUS CAN GRL.

Notes: Elven and Grundt: There are serious problems with name, circumscription, and variation of this amphi-Atlantic species.

The name. - For the last 50-60 years or more, the name Draba norvegica Gunnerus 1776 has been consistently applied to this species. There is no material in the Gunnerus herbarium (TRH) annotated as or conforming to D. norvegica. Gunnerus (1776) referred only to Oeder's "Draba pyrenaica (?)" (Oeder 1764) when describing D. norvegica, which means that Oeder's illustration in Flora Danica (or possibly the material behind the illustration, if any) is the only original material available, i.e., the holotype. We have searched for specimen in C, without luck. Oeder's illustration does not at all resemble D. norvegica as currently considered but rather D. glabella. It is not possible to use this illustration, or Gunnerus' description, to assign the name D. norvegica to the plant currently going by that name. A possible way out of this mess could be to designate an epitype conforming to the current concept of this species. As the diagnosis is not very specific, such an epitype would not be in conflict with the text but would be so with the Oeder illustration. However, we have decided rather to apply the name D. rupestris W.T. Aiton for the species that more recently has been named D. norvegica. See also D. glabella below.

Variation and relationships. - Our opinion is that the variation encountered within D. rupestris is much too large and too discontinuous to be encompassed within one undivided species. Our informal guess is that between 3 and 5 taxa may be involved. As they very often occur sympatrically, sometimes in mixed stands, a racial treatment may be inappropriate. This guesswork finds support in the study of Brochmann et al. (1992). These authors documented D. rupestris (as D. norvegica) to have originated repeatedly. Whether all the variation and polyphyly is at the hexaploid level is uncertain, and plants may have been named as D. "norvegica" when found to be hexaploid.

Two of the major morphs have recently been attempted distinguished in northern Europe as, respectivelly, D. "norvegica" (morph I) and D. arctogena (morph II). Also the latter name is most probably misapplied by, e.g., Elven et al. (2005) and Kristinsson (2008). The morphs differ in leaf pubescence (predominance of simple hairs or more rarely glabrous in morph I vs. predominance of many-branched hairs in morph II), fruit pubescence (glabrous or with simple hairs vs. with forked or more multi-branched hairs), and in general habit including leaf shape, shape of infrutescence (strongly elongating vs. not elongating), and fruit shape. All plants from Bear Island and Jan Mayen, the majority of Svalbard plants, and at least half the plants from Iceland belong to morph II and this morph is also common in the Scandinavian mountains. Morph I is perhaps the most common one in Scandinavia, is frequent in Iceland, and occurs in the warmer fjord parts of Svalbard. Other morphs occur inside or very close to the Arctic, among them one strongly resembling D. lactea but without the minute multibranched hairs on the apical parts of the leaf lower surface. We suspect that a combined morphological and molecular study of D. rupestris will result in it falling apart into several species. In addition, there is morphological evidence for fertile intermediates connecting D. rupestris with tetraploid D. incana (in both Scandinavia and Iceland), predominantly octoploid D. glabella (in Scandinavia), and hexaploid true D. arctogena (in Greenland).

The relationship between D. rupestris and D. arctogena has been disputed. In 2007 we studied the material (in C) that Böcher annotated as D. arctogena (see Böcher 1966a) and found it to belong within the D. cinerea affinity. However, Böcher (1966a) related D. arctogena to D. "norvegica" and reported intermediates in Greenland.

Petrovsky reported plants morphologically similar to and preliminarily identified as D. "norvegica" from Wrangel Island. A further study of this critical material is required as there otherwise are no confirmed records of this species or species group outside the North Atlantic regions (but see Mulligan and Cody 1968).