2  Delimitation and subdivision of the Arctic for Panarctic Flora

2.1  Delimitation

The Arctic has been circumscribed in numerous ways for different purposes, characterized by certain climate(s) or by more or less continuous permafrost, geographically as, e.g., north of the Arctic Circle with some period with 24h day and night, biologically by a special composition in vegetation and/or species, or even politically. For the Panarctic Flora we combine climatic and biological criteria in a rough bioclimatical circumscription, discussed in more detail by Elvebakk et al. (1999). See also other papers in Nordal & Razzhivin (1999).
            We define the Arctic as non-forested areas where growth and reproduction is restricted by a short vegetation period (mostly less than 60–90 days) with low temperatures (nearly always >10°C for the warmest months) and/or low heat sum, and a long winter with stable or nearly stable frost and snow. In regions with continental climates this corresponds to areas north of the polar tree line. We accept, however, that pockets of trees may occur in especially favourable sites in the Arctic and also that bald areas may occur south of the Arctic. In regions with more oceanic climates it becomes problematic. The tree line criterion is not easily applicable there. Surrounding the North Pacific the coasts and islands are non-forested south to N Kamtchatka, the Aleutian Islands, and most of Alaska Peninsula. The same is the case around the North Atlantic where forests are absent from almost all of Iceland, the Faeroes, parts of N British Isles, much of the coast of N Norway, and the east coast of Labrador and south to some parts of Newfoundland. At the same time, sizeable pockets of forest (or at least very tall shrubs) occupy interior fjord in S Greenland. In these areas we have applied the two temperature criteria: (1) middle temperatures for the warmest month (usually July) of less than c. 10°C; and (2) a distinct winter frost climate. By these criteria the following regions are excluded from our concept of the Arctic: In the North Pacific the Commander, Aleutian, and Pribilof Islands, most of the Koryak Coast, and Alaska Peninsula and surroundings; in the North Atlantic most of the Labrador coast and all of Newfoundland, almost all of Iceland (and of course the Faeroes and N Britain), and almost all of mainland Norway.
            We have also excluded from the Arctic those mountain areas where half or more of the bordering lowlands do not fulfill the criteria. Where the mountains run in a N–S direction, this means that our arctic boundary is drawn straight across the mountains, e.g., in the northern Urals between Europe and Asia, Verkhoyansk Mts in E Siberia, and Richardson Mts in NW Canada. This criterion is more problematic where mountains run in a W–E direction, as they do in the Kolyma Mts of NE Asia, Brooks Range in N Alaska, and British Mts in NW Canada. These are commented on below. From a phytogeographical point of view the exclusion of near-arctic mountains is sometimes deplorable as these often are richer in 'arctic' species than more northernly situated and non-forested lowlands (e.g., in N Scandinavia, the Khibiny Mts in C Murman area, Iceland, and NW Canada).
            Our delimitation of the Arctic deviates in one or more aspects from most of those previously applied for botanical purposes. Compared with Löve & Löve (1975: map on p. xi), we are more restrictive in the oceanic regions of Iceland, Labrador, Russian Far East, and partly in continental Siberia, whereas we include the Hudson Bay shores. Compared with Flora Arctica URSS, we exclude many of the areas there considered as arctic in Russian Far East (e.g. the Anadyr basin, the Penzhina basin, and the S Koryak coast) and also some parts in the west in Kanin Peninsula and on the Murman coast. Compared with the authoritative survey of Yurtsev (1994), we follow his delimitation except for the North Atlantic areas where we accept as arctic much of the Murman coast in NW European Russia, small parts of Norway and Iceland, and all of Greenland. This deviation is due to a difference in principles. Yurtsev argued that the North Atlantic areas should be excluded because of the presence there of a number of typically non-arctic species (e.g., Calluna vulgaris and Nardus stricta). Elvebakk and Elven argued that this would be contrary to an application of bioclimatical criteria and result in an imbalance between Atlantic and Pacific regions. They contested the application of floristic criteria and stated that if these were applied, we should also exclude from the Arctic larger parts of the North Pacific coastline at least north to the Bering Strait. Compared with Sekretareva (1999) for the Russian areas, there is an almost exact correspondence between our delimitation and her 'true' Arctic.
            The delimitation as applied by PAF includes as arctic parts of the following countries and regions (with abbreviations used throughout the taxonomic part): Iceland (ICE); Norway (NOR); Russia: European Russia (RUS), Siberia (SIB), and Russian Far East (RFE); USA: Alaska (ALA); Canada (CAN): Yukon Territory, Northwest Territory, Nunavut, Manitoba, Ontario, and Labrador (CAN); and Greenland or rather Kaladlit Nunat (GRL). The delimitation is shown in Fig. ** and includes the following parts of the countries involved:

Iceland (ICE). – The northernmost peninsulas from Hornstrandir in NW to Langanes in NE and the northern offshore islands. The delimitation was proposed by Kristinsson, corresponds with the summer temperature criterion and is unproblematic. However, it excludes the inland mountains with a larger arctic component in their flora.

Norway (NOR). – The Norwegian arctic islands (Jan Mayen Island, Svalbard with Bear Island) and the northernmost mainland peninsulas and islands from Magerøya Island (North Cape) in the west to the Vadsø – Ekkerøya area on the Varanger Peninsula in the east. The delimitation corresponds with the summer temperature criterion but not well with the forest line criterion. There are large non-forested coastal regions west and southeast of our arctic 'strip' but these have higher summer temperatures, in the west also quite mild winters. The delimitation landwards is problematic because the arctic coast borders on low but bald mountains dissected by more or less forested valleys and fjords. The arctic 'strip' is slightly broader than that proposed by Moen (1999). It excludes, however, all of the more interior Scandinavian mountain range (in N Norway, N Sweden, and N Finland) which have a much higher concentration of otherwise arctic plants than the coastal arctic 'strip'.

European Russia (RUS). – In the Murman area the northern half of Rybachi Peninsula, Kildin Island, and the mainland Murman coast of Kola Peninsula from Teriberka in the west to north of the Ponoj River basin in the east. Further east the northern half of Kanin Peninsula, Kolguev Island, Malozemelskaya and Bolshezemelskaya tundras including the lower Pechora River drainage and the Vorkuta area (as borderline arctic), Polar Ural northwards from a line between Ussa River and lower Ob River, Vaigach Island, Novaya Zemlya and Franz Joseph Land. We deviate from some other classifications by including both Polar Ural, the Yugorskiy Peninsula, Vaigach Island, and Novaya Zemlya, in the European parts. The delimitation, except for the Murman area and Kanin Peninsula, mainly corresponds to that proposed by Flora Arctica URSS, by Yurtsev (1994), and by Sekretareva (1999). For the Murman area the same two criteria (treeline, 10°C July isotherm) are applied as for corresponding Norwegian areas and for Kanin Peninsula. It means that the interior Khibiny mountains of Kola Peninsula, fairly rich in arctic plants, are excluded.

Siberia (SIB). – Yamal and Gydan peninsulas and the lowermost courses of Ob and Jenisei rivers (the latter south to Dudinka but excluding the Norilsk area), Taimyr Peninsula north of the Putorana Plateau, Severnaya Zemlya, the lower course of Khatanga River north of (but not including) the surroundings of Khatanga town, lower Anabar and Olenyok rivers, the lower course of Lena River northwards of Chekurovka, the Kharaulakh Mts, the coastal areas between Jana and Kolyma rivers, the lowermost course of Kolyma River, and the Novosiberian and Lyakhov islands. The delimitation corresponds to that proposed by Yurtsev (1994) and Sekretareva (1999).

Russian Far East (RFE). – Areas east and north of a line from the lowermost course of Kolyma River to lowermost Anadyr River (but excluding the Anadyr River basin except for its mouth), Wrangel Island, and coastal areas south of Anadyr along the northernmost Koryak Coast. The delimitation corresponds to that proposed by Yurtsev (1994) and Sekretareva (1999). The boundary as drawn in the mountains runs more or less along the watershed north of the Anadyr River basin. This is problematic as we have applied a different criterion in Brooks Range on the American side. It is also worth notice that the Anadyr River basin is excluded whereas coastal areas both north and south of the Anadyr estuary are considered as arctic. The southern limit on the Koryak Coast is quite arbitrary.

Alaska (ALA). – The Bering Sea islands of St. Matthew, St. Lawrence and Little Diomede, the west coast northwards from (but excluding) Cape Constantine in the Bristol Bay area, across the Yukon River delta to Saint Michael on Norton Sound, Seward Peninsula west of Moses Point, the Kotzebue Sound area, and all areas north of the treeline on the south slope of Brooks Range to the Canadian border. In the north and west this delimitation corresponds to the treeline, with some problems in Brooks Range. In the southwest the delimitation towards more oceanic areas is arbitrary. The delimitation is very close to that applied by Löve & Löve (1975) and by Yurtsev (1994).

Canada (CAN). – All of the Arctic Archipelago. On the mainland British Mts and northern Richardson Mts south to the treeline north of Porcupine River and Old Crow Flats and west of Mackenzie River, the non-forested parts of the Mackenzie River delta, and then north of a line from north of Inuvik, north of Great Bear Lake, and northeast of Great Slave Lake, to Hudson Bay north of Churchill, Hudson Bay islands and shores from Churchill east to northeast of Belcher Island (but excluding James Bay), Ungava Peninsula south to Minto Lake (but excluding the head area of Ungava Bay), and the northernmost tip of Labrador north of Hebron. The delimitation corresponds to the treeline but with problems at Hudson Bay and perhaps in the more oceanic areas of E Labrador, see below. This delimitation also largely corresponds to that of Yurtsev (1994).

Greenland / Kaladlit Nunat (GRL). – All of Greenland is included. The very few taxa restricted to the small inland forested enclaves in the southwestern parts are included in the Checklist but mostly with notes on their borderline character. There is a large deviation as compared with Yurtsev (1994) as he excluded all of S Greenland from the Arctic.

2.2  Floristic regions

In Part B (Distribution) the Arctic is further subdivided in two ways: floristic regions, depending mainly on chorology and past history, and vegetation zones, depending mainly on bioclimate. Both are mapped by Elvebakk et al. (1999) and the floristic regions by Yurtsev (1994), but some modifications have later been made to both classifications.
            The floristic regions are circumscribed so as to have common features independent of the general thermic south – north variation, features that we assume to have mainly historical causes. Some of these regions cross the national borders. Many of the delimitations have been much debated and are still controversial among the PAF collaborators, see comments below. The regions applied for the Checklist phase are shown on maps in Figs. **-**:

North Iceland – Jan Mayen (Ic)
The N Iceland peninsulas and the Norwegian island of Jan Mayen. The Icelandic part is an oceanic region with some local features, floristically different both from SE Greenland and from Scandinavia. The Atlantic European element is stronger than in any other region, probably due to the comparatively mild winters. The short history since the last glaciation and the frequent disturbance by volcanism give a distinct character to the Icelandic flora. There are no endemics at species level, but often the Icelandic plants are subtly different from their counterparts in NW Europe, perhaps recognizable at ranks of subspecies or variety. Floristically, Iceland has relations both to Greenland and Europe, but the European influence is the strongest. No parts of Iceland were accepted as arctic by Yurtsev (1994), but the climatic and vegetational conditions in the northernmost parts correspond to those found in parts of the Beringian area considered by him as arctic.
            Yurtsev (1994) and later proposed the young, actively volcanic island of Jan Mayen as a separate region. It is by us merged with N Iceland for practical reasons. Jan Mayen is very poor in species (Lid 1964) and negatively defined as 97–98 % of its vascular plants are in common with all three neighboring areas: E Greenland, N Fennoscandia and N Iceland. The main reasons for inclusion in 'Ic' are then that it is part of the same geological (volcanic) mid-Atlantic structure and that it does not deserve rank as a separate region.

North Fennoscandia (FN)
Northeasternmost mainland coastal Norway and the Murman Coast in NW European Russia. The Sør-Varanger area of Norway and the central Kola Peninsula mountains as well as much of the mainland Murman coast and fjord heads are excluded due either to frequent occurrence of woodlands or too high summer temperatures. Parts of this coast have Middle Boreal characters with some occurrences of quite thermophilous species. Some Atlantic European species reach the western parts whereas the main components are boreal European – W Siberian plants. The parts we accept as arctic have a gradient in climate from oceanic in the west to continental on the east, connected with colder seas with winter ice cover in the east. The region is poor in Siberian floristic elements present in the next region (these are actually better represented inland in N Fennoscandia, away from the arctic coast). The entire region also has had some influx of taxa from the Scandinavian mountain range. The region has been heavily glaciated during all the main Pleistocene glaciations, and there are very few regional endemics at rank of species, perhaps none (except for agamospecies) in the arctic parts. This region was excluded from the arctic by Yurtsev (1994) but is arctic according to the PAF criteria.

Kanin – Pechora (KP)
NE European Russia. A lowland region that includes Kanin Peninsula (northern and major part), Malozemelskaya and Bolshezemelskaya tundras (the so-called 'Terra Samojedorum'), the lower parts of the Pechora River drainage, and Kolguev Island. A continental NE European region with more pronounced Siberian floristic influence than found in Fennoscandia but still with a strong European – W Siberian element. Also this region has been heavily glaciated but has a few endemics at rank of species. There are some problematic borderline arctic occurrences of boreal plants in the Pechora drainage.

Svalbard – Franz Joseph Land (SF)
Norway and European Russia. The high arctic Norwegian islands of Svalbard (Spitsbergen and surrounding islands, Bear Island) and the Russian islands of Franz Joseph Land.
            The flora of Bear Island (Engelskjøn & Schweitzer 1970, Elven & Elvebakk 1996) combines features of N Scandinavia and Svalbard proper but is depauperate due to a foggy and unfavourable climate. The fairly large archipelago of Svalbard is much richer (but still poor compared with other regions) and combines floristic elements of arctic Russia and Greenland, but with comparatively few connections to mainland Scandinavia. Several predominantly North American and Greenlandic species have their only Eurasian occurrences either here or her and in Russian Far East. These island groups have been heavily glaciated during Pleistocene, perhaps with some refugia along the west coast. The number of endemics at species rank is very low and those found are probably of fairly recent origin.
            The archipelago of Franz Joseph Land has been and still is very heavily glaciated and is negatively defined floristically. All its known taxa are in common with Svalbard.

Polar Ural – Novaya Zemlya (UN)
NE European Russia. Includes Polar Ural (the northernmost extension of the ancient Ural mountain range), Yugorskiy Peninsula, Vaigach Island, and the two islands of Novaya Zemlya.
            Most or all of the areas have been glaciated during Pleistocene but with comparatively short distances to non-glaciated parts of the Urals. The region is transitional floristically between arctic Europe and Asia but with a separate mountain range element connected to the Urals. Some N Urals endemics reach or are confined to the arctic parts whereas proposed endemics in Novaya Zemlya are dubious.

Yamal – Gydan (YG)
NW Siberia. A lowland region that includes the two NW Siberian peninsulas of Yamal and Gydan, the lowermost reaches of Ob River, and the hilly plains between Polar Ural and Jenisei River.
            Most or all of this region seems to have been glaciated one or more thimes during Pleistocene (also during the last glaciation) but is close to the eastern limit of the N European Weichselian Ice Shield. The region has a stronger European – W Siberian floristic element than the other parts of N Siberia and also a specific W Siberian element, often along Ob River, absent from areas further east. A main and for us problematic feature is the lowermost reaches of Ob River where numerous more southern species reach or border on the Arctic. The boundary along the lower Ob should perhaps have been drawn further north than proposed by Yurtsev.
            The eastern boundary is also problematic. The boundaries between several Siberian regions have been drawn in the middle of major rivers. Jenisei River separates between the regions Yamal – Gydan (YG) and Taimyr – Severnaya Zemlya (Tm), Khatanga River between Taimyr – Severnaya Zemlya and Anabar – Olenyok (AO), Lena River between Anabar – Onelyok and Kharaulakh (Kh), and Kolyma River between Kharaulakh and W Chukotka (CW). This means that homogeneous floristic elements that follow the rivers and river valleys in most cases are split on two regions. It is also often difficult to decide from the collections, and from the published distribution maps, on which side of the river they have been collected.

Taimyr – Severnaya Zemlya (Tm)
N Siberia. Includes the Severnaya Zemlya and Kirov island groups and Taimyr Peninsula between Jenisei and Khatanga rivers and north of the Putorana Plateau. The boundary runs north of Norilsk and Khatanga towns but across the settlement of Dudinka (which thereby becomes an important borderline site).
            The mainland area is a phytogeographically very rich region with several endemics in the river valleys and in the central Taimyr Byrranga Mts, and with floristic connections southwards over the Putorana Plateau and the Central Siberian highlands to Central Asian mountains. The distinct element of endemics present in the Putorana and Taimyr regions is probably due to short-durating and intermittent glaciations with several refugia. Several endemics are also found along Jenisei and partly Khatanga rivers. Many border occurrences are found along the lower reaches of Jenisei and Khatanga rivers.
            The islands of Severnaya Zemlya are high-arctic, species-poor, and probably without distinguishing floristic elements.

Anabar – Olenyok (Ao)
N–NE Siberia. A lowland region between Khatanga River in the west and Lena River in the east, including the Lena River delta.
            This region and those following are outside the heavily glaciated parts of northern Eurasia. There are some connections to the Central Siberian highlands and in addition a strong floristic element that follows Olenyok and Lena rivers where many border occurrences are found along their lower reaches, on both banks of Lena. Some endemics are found in the Khatanga and especially the Lena river valleys. Otherwise the region is comparatively species-poor and little characterized compared both with Taimyr in the west and Kharaulakh in the east, perhaps also less botanized.

Kharaulakh (Kh)
NE Siberia. A very small region that includes the northernmost extension of the Verkhoyansk Mts along the right bank of Lena River, continuing in the Kharaulakh Mts north to include the Tiksi area and the west side of Buorkhaya Bay.
            This is a floristically strongly deviant and species-rich region with a major connection southwards to the E Siberian mountains. The number of endemics is higher than in the more westernly regions, partly connected to the Lena River valley, partly to the Verkhoyansk – Kharaulakh Mts. There are delimitation problems both along Lena River and in the mountains. In addition, the boundary in the Russian proposal (which we have accepted for the Checklist) is drawn about 100 km south of the actual treeline in the region. This means that we have had to include a very large element of borderline cases for this region.

Yana – Kolyma (YK)
NE Siberia. The lowlands from the Tiksi – Buorkhaya region eastwards to Kolyma River, including the Novosiberian and Lyakhovsky island groups.
            This is a swampy, little botanized, and comparatively weakly characterized region but with some Beringian elements not known further west, especially along the Kolyma River drainage. Some boreal elements follow the rivers, especially Yana, Indigirka and Kolyma rivers, but along Kolyma River it is often difficult to tell on which side they have been found. The islands have a depauperate flora with few if any characterizing elements.

W Chukotka (CW)
Russian Far East. This region east of Kolyma River is also often named Continental or N Chukotka. Compared with Yana – Kolyma, it is mainly mountainous except for coastal plains around Chaun Bay. It includes the arctic parts of Anyui and Anadyr mountains up to the watershed and the southern boundary is arbitrary.
            This is the northern extensions of the major NE Asian mountain ranges and with a very strong and distinctive NE Asian floristic element, in addition to many amphi-Beringian taxa. The number of endemics is high. It is amply characterized floristically.

Wrangel Island (WI)
Russian Far East. The region consists of the isolated Wrangel Island and the nearby Herald Island.
            Recognized as a region of its own, mainly due to an element of endemics and of disjunctions, partly connecting to NW North America. The treatment of Wrangel Island and its taxa is strongly influenced by a hypothesis that this is a major part of a large pre-Weichselian and perhaps pre-Quaternary shelf area with perhaps the strongest palaeo-element in the flora of the entire Arctic. Some of the Wrangel Island endemics may, however, not survive a critical comparison with plants in other (also North American) areas where less narrow species circumscriptions are applied. The alternative is to merge this region with W Chukotka. In any case, this island is very species-rich and with a special species composition very different from the other islands and island groups north of Asia.

S Chukotka (CS)
Russian Far East. The region includes the southern part of the main Chukotkan mountains, the Anadyr River basin, and the Koryak mountains and coast. Only a small part of it is defined as arctic, north and east of the woodlands and shrublands ('stlanik', Pinus pumila shrubs) in the Anadyr basin.
            This region is more oceanic ('Pacific') than the other Russian Far East regions. It comprises three parts: (1) A coastal part of hills and mountains north of the Anadyr River estuary, inland including the floristically rich Pekulnei Mts W of Belaya River; (2) A coastal part bordering on the Koryak Mountains south of the Anadyr River estuary; and (3) A mountainous part north of Anadyr River and west of the major northern tributary Belaya River. The region is thereby heterogeneous. Part (1) floristically combines Koryak Coast elements and more clearly Beringian ones from E Chukotka. Part (2) is the most oceanic and has major connections to the main Koryak Coast and further southwards to Kamtchatka. Part (3) is mainly intermediate between the boreal Anadyr River basin and the W Chukotkan Anadyr Mts in the north. Each of these part areas have their own endemic elements.
            During the Checklist process it has been proposed to omit S Chukotka as a separate region and to assign part (3) to W Chukotka and parts (1) and (2) to E Chukotka. We retain it, however, as a separate region for the Checklist, mostly because the coastal parts are comparatively rich in plants with a Koryak – Kamtchaktan Pacific connection not found elsewhere in the Arctic.

E Chukotka (CE)
Russian Far East. The region has also been named Beringian Chukotka and consists of Chukchi Peninsula (including Big Diomede Island), areas west of Amguema – Paljavaam rivers, and an area around the northern parts of Anadyr Bay.
            This region has the strongest Beringian (and NW North American) element of all Russian regions, a large number of regional and local endemics, and is well characterized floristically. However, a merger with the W Alaskan region has been discussed during the Checklist process. Chukchi Peninsula is very close floristically to Seward Peninsula and other parts of W Alaska.
            For the Bering Sea islands, see the next region.

W Alaska (AW)
Alaska. The region includes the coastal, non-forested parts of W Alaska from Bristol Bay in the south to Icy Cape on the Arctic Coast in the north, including the southwestern, not forested extensions of Kuskokwim Mts, the outer parts of the Yukon River delta, Seward Peninsula, the areas from Kotzebue northwards, and the westernmost parts of Brooks Range west of about 159–160°W.
            This is the American region with the strongest Beringian (and NE Asian) element. It clearly connects to Chukchi Peninsula floristically, and some authors (e.g., Hultén) considered these two as parts of one phytogeographical region. There are, however, also some distinct floristic differences between the two sides of the Bering Strait, even if the isolation is less than 10,000 years old. The number of regional and local endemics is high.
            Two parts of the region cause borderline occurrence problems: the Yukon River delta, where the boundary is drawn very arbitrarily, and the southernmost coast along Bristol Bay with numerous American Pacific elements absent elsewhere from the Arctic.
            The Checklist deviates from Yurtsev's original proposal in the treatment of the northern Bering Sea islands: St. Matthew, St. Lawrence and the Diomedes. These were considered as a separate floristic region by Yurtsev (1994). All these islands are floristically mainly negatively characterized, with only 3–4 more or less specific taxa, but with distinct connections to the more southern and non-arctic Pribilof and Aleutian islands. We have decided to apply the same principles here as for two other mainly negatively defined areas, e.g., Jan Mayen Island and Franz Joseph Land in the North Atlantic and Barents Sea regions. For practical reasons, we have included the American islands in W Alaska, the Russian Big Diomede Island in E Chukotka. The problem with this solution is that the boundary between the regions along the Bering Strait becomes fully artificial, more so than most of the other boundaries. It runs between the botanically very similar Russian Big Diomede and American Little Diomede. Also St. Lawrence Island has some Asian element absent from the Alaskan mainland.

N Alaska – Yukon (AN)
Alaska and Canada. The region includes in Alaska the areas north of the treeline in the Noatak River valley, Brooks Range, and the Alaskan Arctic Slope and Coast, in Canadian Yukon and Northwest Territory the British Mts and northern Richardson Mts eastwards limited by the Mackenzie River plain. The eastern boundary runs along the woodland limit in the eastern foothills of Richardson and British mountains, which means that the unforested parts of the Mackenzie River delta and plain is included in the next region. This is a deviation from the principles applied in Siberia.
            The Beringian influence is strong and separates this region floristically from the Central Canadian one as this element shows a very marked decrease when crossing the 'Mackenzie Line'. The Cordilleran influence is also strong and characterizes this region compared with both W Alaska and C Canada. The number of regional endemics is comparatively high, but there is also a number of lowland and coastal endemics shared with the NW Canadian islands (perhaps 'shelf' endemics). Comparatively many borderline occurrences are found in Brooks Range where it is difficult to draw a boundary due to the long and deep valleys running in a S–N direction.

Subdivision of arctic Canada
The subdivision of arctic Canada (and partly Greenland) has been very much disputed during the Checklist process. Yurtsev's original proposal was to recognize four regions: (a) A northwestern 'Central Canadian' region of the arctic parts of District of Mackenzie east to W Boothia Peninsula and the western islands east to and including Somerset, westernmost Devon, and Ellef and Amund Ringnes islands; (b) A 'West Hudsonian' region of District of Keewatin from the eastern limit of region (a) to the middle of Hudson Bay and including Southampton Island, Melville Peninsula and N Baffin Island; (c) A 'Baffin – Labrador' region including the areas east of the middle of Hudson Bay and S Baffin Island; and (d) An 'Ellesmere' region of central and eastern Devon, Axel Heiberg, and Ellesmere islands. The arguments for this division were, among others, that Atlantic elements disappeared some distance west of Hudson Bay, that very few Beringian elements reached the west coast of Hudson Bay, that the areas east of Hudson Bay had a combination of amphi-Atlantic and eastern American elements absent from the areas west of Hudson Bay, and that there was a small endemic element centered on Ellesmere and Devon islands.
            Canadian arguments against this division were, among others, that: (1) The line between Yurtsev's 'Central Canadian' and 'West Hudsonian' runs through a very homogeneous area both on the mainland and in the islands; (2) The line between 'West Hudsonian' and 'Baffin – Labrador' in the middle of Hudson Bay divides on two regions a very strong element connected especially to the shores and lowlands surrounding Hudson Bay on both sides, and that the same line in Baffin Island is without phytogeographical significance; and especially that: (3) The division is based on an evaluation of Beringian and Atlantic elements without taking into account that a very large part of the North American flora is North American, not consisting of transgressing Asian and European taxa. Canadians proposed not to subdivide arctic Canada (except for the 'Mackenzie line'), a solution that would give an unwanted imbalance in size and variation between the regions on the North American and the Asian and European sides.
            There might be some useful evidence for recognition of floristic regions in past refugia and immigration routes. The western Cordilleras (Rocky Mts etc.) contribute a significant floristical element which, together with Beringian refugial taxa, justifies separation of the W Alaska and the N Alaska – Yukon regions. A parallel but much weaker eastern Cordilleran (Appalachian) element occurs in, e.g., NE New England (especially in White Mts in New Hampshire), Gaspé Peninsula, Newfoundland and Labrador, but it scarcely penetrates to Baffin Island and is insufficient for characterization of an arctic region.
            Possible refugial areas have been identified or indicated in: (A) The (partly mountainous) main Beringian area that reaches east to the 'Mackenzie Line'; (B) A refugial shelf area that connects the westernmost islands ‑ W Banks and Victoria (perhaps also Melville and Prince Patrick islands) ‑ and the western mainland coast as far east as to the Liverpool Gulf; (C) A possible outer, northern island refugium that consists of Parry and Sverdrup islands and which might stretch to N Greenland; and (D) A source area connected to the eastern Cordilleras at least from New Hampshire to Labrador. In addition, the Hudson Bay lowlands and Ungava is very strongly influenced by an influx of boreal to low arctic and generally North American taxa.
            The Checklist solution is a compromise and is perhaps equally unsatisfactory for almost all participants. Some comments are given for each region below.

Central Canada (CC)
Canada. The region includes the mainland from (and including) the Mackenzie River plain in the west to Melville Peninsula and approaching Hudson Bay in the east, and the Canadian Arctic Archipelago except for the southernmost part of Baffin Island south of Cumberland Sound (included in Hudson Bay – Labrador) and Devon and the eastern Sverdrup islands (Axel Heiberg, Ellesmere, included in Ellesmere Land – N Greenland).
            As now circumscribed the region is fairly 'natural' on the mainland but problematic in the islands. The western larger islands (especially Banks and Victoria) and the mainland areas east to Cape Bathurst deviate from the main central body by having a relictual element that may have an origin on the glacial shelf. Parts of this element are endemic. The line across Baffin Island is more of a south – north boundary than anything else, i.e., zonal. The separation of Devon and the eastern Sverdrup islands from the others is based on very few criteria and is also partly zonal.
            There is a major area of borderline occurrences is the Mackenzie River delta, partly also with local endemics but at fairly low rank. Much borderline taxa also occur close to Great Bear Lake.

Hudson Bay – Labrador (HL)
Canada. The region is a lowland region that consists of the shores and islands of Hudson Bay, including Southampton Island and the small surrounding islands, Ungava Peninsula, northernmost Labrador Peninsula, and southernmost Baffin Island south of a line from south of Cumberland Sound to Foxe Basin.
            The boreal American influence is especially strong in this region, in addition to some eastern Cordilleran influence in the east. The most problematic part of this region is Hudson Bay and its summer cooling effect. The forest reaches a fair distance north along Hudson Bay on both sides but there is a narrow non-forested coastal strip along almost all of the southern shore. The two alternatives are either to draw a boundary line across the bay between the treelines on the two sides (as applied by Löve & Löve 1975) or to include the southern non-forested coast. We have followed the latter course for the Checklist, but this results in an extreme concentration of borderline arctic occurrences along S Hudson Bay due to the very sharp gradient from arctic waters and shores to boreal and forested inland. In addition, there are some Hudsonian endemics, probably of a young age, connected to the Hudson Bay and James Bay shores.

Ellesmere Land – N Greenland (EP)
Canada and Greenland. The gap between Ellesmere Island and NW Greenland is narrower than between many of the larger Canadian islands and also ice-covered most or all of the year. The phytogeographical connection is very close, and a common refugial history is also indicated. We have therefore considered the NE Canadian islands and N Greenland ('Peary Land') as one floristic region, in Greenland delimited southwards as done for N Greenland in Danish and Greenlandic treatments.
            Even if most of the region is high arctic, interior parts of Ellesmere Island have a remarkable favourable climate and rich flora compared with other areas at 80°N. A small endemic element characterize it, but this element is not fully confined to this region.

W Greenland (GW)
Greenland. The region includes western and southernmost Greenland, in the south delimited towards E Greenland along Lindenow Fjord in SE Greenland. All the Greenland forest enclaves are located in W Greenland as here defined.
            Floristically, W Greenland is connected westwards towards Canada, partly also southwestwards towards the eastern Cordilleras and Labrador – Newfoundland. There is, however, a fairly distinct local (endemic) element that characterizes it relative to the Canadian regions and also differentiates it well from E Greenland.

E Greenland (GE)
Greenland. E Greenland is quite efficiently isolated from W Greenland by the inland ice cap, in the north also at present isolated from N Greenland by large glaciers that reach the sea. The transition in the south, around Lindenow Fjord, is more gradual. The region is floristically distinctly more connected to Europe and to the Eurasian Arctic than is W Greenland and also N Greenland. There is a small element of endemics, all probably of hybridogeneous and very recent origin.

2.3  Vegetation zones

The vegetation zones reflect the mainly thermically determined changes in the S–N direction. The criteria are summarized by Elvebakk (1999). We have found a division into five zones practicable, where each of the zones reflects an approximately 2°C decrease in mean temperature for the warmest month from c. 10°C at the thermic forest limit to less than 2°C in the northernmost zone. The zones are named differently in different traditions. For the Checklist, we have therefore decided to design them in the distributional tables just with letters, from A (the northernmost) to E (the southernmost), but below are also included the three name proposals by Elvebakk (1999, a-c) and the names proposed by Yurtsev (1994, d). The first name proposals (a) are the ones preferred by the majority of the Editorial Board and are underlined. The distribution of the zones is shown in Fig. **.

Zone A
a) Arctic polar desert zone; b) Arctic herb zone; c) Northern high arctic zone; d) High-arctic tundras.
            Mean warmest month temperature mostly < 2°C. Scattered vegetation of forbs and graminids, more abundant mosses and lichens. Woody plants are normally totally absent. The species diversity is low and the zone is probably entirely without exclusive phanerogams.
            We apply the 'polar desert' concept differently from often done in North American literature by referring to thermic conditions only, not to the open vegetation which also can be caused by draught or unfavourable substrate. A possible explanation of the lack of special floristic characteristics is that this zone may have been nearly absent during the Postglacial Hypsithermal with much higher temperatures than today.
            The zone is present in the Norwegian Svalbard islands, the Russian islands of Franz Joseph Land, northern Novaya Zemlya, Severnaya Zemlya, and as a very narrow zone on mainland Taimyr Peninsula (see Razzhivin 1999, note that the zone is absent from arctic Russia east of Taimyr), in the northwestern Canadian Arctic Archipelago, in northernmost Ellesmere Land, and as a narrow zone in northernmost Greenland.

Zone B
a) Northern arctic tundra zone; b) Arctic prostrate shrub zone; c) Middle high arctic zone; d) Northern arctic tundras.
            Mean warmest month temperature mostly 2–4°C. Mostly open vegetation of forbs, graminids, prostrate or 'subterranean' shrubs (Salix polaris), and often luxuriant moss and lichen vegetation. The species diversity is much higher than in zone A but still low. Very few if any species are restricted (endemic) to the zone but some arctic endemic species reach it. This zone may also have been much depauperated during the Postglacial Hypsithermal.
            The zone is present in the Norwegian Svalbard islands, the Russian Novaya Zemlya, Novosiberian, and Lyakhovskiy islands, some narrow mainland coasts in W Siberia eastwards to Taimyr, and in northern parts of the Canadian Arctic Archipelago and Greenland.

Zone C
a) Middle arctic tundra zone; b) Northern arctic dwarf-shrub zone; c) Southern high arctic zone; d) Southern arctic tundras.
            Mean warmest month temperature mostly 4–6°C. Open to often closed vegetation of dwarf-shrubs, prostrate shrubs, graminids and forbs, often also cryptogam-dominated. The species diversity is comparatively high (the increase from zone A to zone C is much steeper than from zone C to zones D and E). There are several species endemic to this zone.
            The zone is present in the Norwegian arctic islands (Jan Mayen, Svalbard, and Bear Island), in Russian southern Novaya Zemlya, Vaigach and most mainland regions from Yugorskiy Peninsula eastwards to West Chukotka, the northernmost tip of Alaska, most of the Canadian Arctic Archipelago and mainland Canada from Boothia Peninsula to the tip of Ungava Peninsula, and in C Greenland.

Zone D
a) Southern arctic tundra zone; b) Southern arctic dwarf-shrub zone; c) Northern low arctic zone; d) Northern hypoarctic tundras.
            Mean warmest month temperature mostly 6–8°C. Closed vegetation with dwarf-shrubs and graminids as predominant elements, low thickets (Salix, Betula nana, Juniperus communis) and marshes. The species diversity is not very much higher than in zone C, probably partly due to more competition in the denser vegetation cover. A number of endemics are found, but few are restricted to this zone.
            The zone is present in all of mainland Russia from the Pechora area (and northern Kolguev Island) east to E and northern S Chukotka, in northern W Alaska and much of N Alaska, in Canada in southern Banks and Victoria islands and much of the arctic mainland, in southernmost Baffin Island, and in C to S Greenland.

Zone E
a) Arctic shrub tundra zone; b) Arctic low-shrub zone; c) Southern low arctic zone; d) Southern hypoarctic tundras.
            Mean warmest month temperature mostly 8–10°C. Closed vegetation where mires, heaths and thickets of erect shrubs (mainly Salix, Betula, Alnus) often dominate. The total species diversity is much higher than in zone D, mainly due to arctic transgression of otherwise boreal taxa and in some regions of taxa from neighboring mountains. The boreal transgressions may partly be remanings from the Postglacial Hypsithermal.Mountainous areas in this zone in N Asia and NW North America have the highest number of endemics in the Arctic.
            The zone is the only one present in N Iceland, mainland N Norway, and Russian Murman area and occurs all the way further eastwards to S Chukotka (but mapped as very narrow to nearly absent in most of Siberia), in most of W Alaska and all of Brooks Range in N Alaska, as a broad zone in mainland Canada and as a very narrow zone along Hudson Bay, in the eastern Canadian peninsulas, and in S Greenland.

In the distribution tables are also included occurrences in immediately neighboring boreal and alpine areas (as N).

The floristic regions and the bioclimatic zones are combined in the following way in the table below: *** – constitutes a major part of the region (50% or more); ** – constitutes an intermediate part (20–50%); * – constitutes a smaller part (less than 20%); x – bordering on the boreal. Zones: A – Polar desert, B – Northern Arctic, C – Middle Arctic, D – Southern Arctic, E – Shrub tundra, N – Boreal and/or Boreal – Alpine. The isolated zone C occurrence in region N Iceland (Ic) is the island of Jan Mayen.