Panarctic Flora

640801 Dryas octopetala L.

• L., Sp. Pl.: 501 (1753). Lectotype (LINN): Herb. Linn. 658.3 (Barrie in Jarvis et al. 1993: 44). See notes.
• Dryas octopetala subsp. subincisa Jurtz., Fl. Arct. URSS 9, 1: 322, 265 (1984). Holotype (LE): Siberia: "in cursu inferiore fl. Ob prope pagum Obdorsk, inter fl. Chanema Magna et terminum orientalem Urali", 20. July 1924, leg. B.N. Gorodkov 406.

2n= 18 (2x). - Europe, Russia (N), Greenland? - Numerous reports.
For reports from Greenland by Böcher (1938b, eastern Greenland), Böcher and Larsen (1950), and Jørgensen et al. (1958, northeastern Greenland), see the doubts about the affinity of Greenland plants.

Geography: Amphi-Atlantic (E)? - European - Asian (NW): ICE NOR RUS SIB GRL?

Notes: Elven and Murray: Dryas octopetala was described from "Alpibus Lapponicis, Helveticis, Austriacis, Sabaudicis, Hibernicis, Sibiricis" (Linnaeus 1753). Barrie (in Jarvis et al. 1993) did not state the origin and characters of the type specimen but we assume that it is European.

Yurtsev (PAF proposal) assigned all arctic material of D. octopetala from eastern Greenland east to northwestern Siberia to subsp. subincisa. For the Atlantic regions, he specifically mentioned Greenland, Svalbard, northern Scandinavia, and with question marks the Faeroes and the British Isles, but he excluded the plants of southern Scandinavia and central and southern Europe. Yurtsev assumed subsp. subincisa to possibly be a product of hybridization between D. octopetala subsp. octopetala and D. incisa (but then mainly distributed outside the accepted ranges of both D. incisa and his concept of D. octopetala subsp. octopetala). The diagnostic characters reported are, in our opinion, not very striking (leaves narrower and smaller, with revolute margin etc.).

The molecular and phylogeographic results of Skrede (2004) and Skrede et al. (2006) could be used to support Yurtsev's proposal of two taxa at some rank but not with the ranges and morphological characters reported by him. Two branches are suggested by the AFLP data within the major European and Siberian octopetala group. The first branch consists of the plants of western, central, and northern mainland Europe and Iceland, suggesting a postglacial migration of D. octopetala to northern Europe from southern and/or central Europe after the last glaciation along two major routes: one over the British Isles to Iceland and one more continental that reached all of Scandinavia. The type of D. octopetala, if from mainland Europe (as we assume), belongs to this branch. The second branch consists of the plants of north-central and northwestern Siberia (from northern Yakutia westwards), northern European Russia, Svalbard, and perhaps also slightly represented in a few populations in the North Cape area in arctic mainland Norway. The type of D. octopetala subsp. subincisa is from within the range of this branch. There is no factual evidence of hybridogeneous partaking of another species (D. incisa) in this branch. The two branches are better interpreted as results of separation south and east of the northern European ice shield during the last glaciation(s). The molecular results could be used to support two subspecies but would assign (almost) all the mainland European plants to subsp. octopetala (as opposed to Yurtsev's proposal) and the northernmost European Russian and the Svalbard ones to subsp. subincisa. There may be some morphological support for this solution, but we refrain from acceptance of the subspecies because Yurtsev drew the morphologically based line within the range of the western and central European branch. If races are accepted, subsp. octopetala occurs as arctic in Iceland, mainland Norway, and in the Murman area in northwestern European Russia, whereas subsp. subincisa occurs in Svalbard, northeastern European Russia, northwestern and north-central Siberia, and perhaps very locally in northern Norway (and probably in the northernmost parts of the Murman area).

A problem not yet solved is that the northeastern (northern Russian and Siberian) branch in molecular data also includes, besides D. octopetala, material from northern Yakutia identified as both D. incisa and D. punctata. This may be explained in three ways: as a diversification of the "incisa" and "punctata" features subsequent to the separation between the central and western European and the northern Russian and Siberian branch of D. octopetala, as some but not predominant introgression from Beringian plants into the northern Siberian Dryas, or as a result of isolation in Europe of only a restricted part of the original variation of a morphologically more varied branch. We tend to favour the last-mentioned hypothesis (i.e., a 'bottleneck' or a 'founder' effect).

The plants in eastern Greenland are enigmatic. Plants that obviously belong to the D. octopetala aggregate has a small but fairly compact range there. Except for this small area, the D. octopetala aggregate is absent from Greenland and from North America east of the Mackenzie, replaced by D. integrifolia. Hybrids D. integrifolia x octopetala s. lat. occur within a wider range in eastern, northern, and northwestern Greenland, suggesting a previously wider range of the D. octopetala aggregate that may have been overrun by D. integrifolia. These Greenland plants of the D. octopetala aggregate resemble the Svalbard D. octopetala morphologically but connect to the Beringian (D. ajanensis) main group in AFLP markers. In one of his comments to the genus above, Yurtsev pointed out the occurrence of Pleistocene subfossil leaves of the D. octopetala type from sites in Greenland and northern Canada currently occupied by D. integrifolia only. A very tentative hypothesis is then that the eastern Greenland populations may be a remnant from a range of the D. octopetala aggregate throughout arctic North America and Greenland before the last glaciation(s). A perhaps more probable hypothesis is introgression from D. integrifolia.

Two smaller matters. A canescent form is proposed by Yurtsev as D. octopetala subsp. subincisa Jurtz. var. argentea (Blytt) Jurtz., described from Norway. Yurtsev: "The distribution is to be checked".

It is probable that D. octopetala hybridizes with D. punctata. Such hybrids have been described as D. x vagans Juz. in Kom., Fl. URSS 10: 459 (1941), were mapped by Yurtsev (1984c) from Taimyr west to the Norwegian border, and also indicated by Yurtsev (PAF proposal) from mainland Norway, Svalbard, and Greenland. We are reluctant to accept these hybrids outside the overlapping range of the species and would rather consider the characters on which such reports are based as gene geography. Material identified as D. x vagans by Yurtsev from northern Europe falls inside the normal morphological variation pattern of the two branches of D. octopetala in our concept, supported by AFLP markers (Skrede et al. 2006). See also Siegismund and Philipp (1999).

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  Source: Michael Haferkamp at Wikispecies