Panarctic Flora

361225-28 The Ranunculus acris aggregate R. acris, R. glabriusculus, R. subborealis, R. turneri

Geography: Amphi-Atlantic - European - Asian - amphi-Beringian.

Notes: We are in doubt how to treat this widespread aggregate, either as one mega-species Ranunculus acris (as done by Hultén), as five or more species (as done by the majority of Russian authors until recently), or as something in between. A combined morphological and molecular investigation is needed to resolve this group. The treatment below is provisional.

The R. acris aggregate is sexual and is mainly Eurasian but reaches as native both across the North Atlantic to Greenland and across the Bering Strait and North Pacific to northwestern North America. The morphological variation pattern is complicated. Several species or races have been described, the major arctic ones (with places of description): R. acris s. str. (Europe), R. glabriusculus (northern European Russia), R. borealis auct. (= R. subborealis, northern Russia), R. pumilus (Scandinavia), and R. turneri (the Yukon Territory).

Hultén (1971a) and Hultén and Fries (1986) accepted two species only, the Pacific R. grandis Honda from northern Japan north to the western Aleutian Islands and a widely circumscribed R. acris with four subspecies: subsp. acris in Europe and western Siberia and also in Greenland, subsp. pumilus in all of northern Eurasia and in northwestern North America (thereby including R. borealis or R. subborealis, R. glabriusculus, and R. turneri as considered by other authors), subsp. japonicus (Thunb.) Hultén as widespread in eastern Asia south of the Arctic, and subsp. nipponicus (Hara) Hultén from northern Japan to southern Kamtchatka. No type for the name "pumilus" was designated at Hultén's time and the meaning of the name was not established. Hultén's circumpolar, inclusive treatment of the aggregate has not found support among other researchers but it has some support in the close morphological connections between the proposed taxa. Even if the extremes - the western European R. acris and the Beringian R. turneri - are clearly different, their distinctness largely disappears when plants in the connecting areas are considered. Other treatments are regional:

North America. - Whittemore (1997) accepted two species: R. turneri (= R. turneri subsp. turneri in the Russian approach) and R. acris. He commented that the majority of the North American plants of R. acris have their origin in introductions from Europe but that the species may be native in Greenland and in the Aleutian Islands (the latter the same as R. grandis of Hultén and Fries 1986). He did not comment further on the (arctic) Greenland plants.

Russia. - Rebristaya and Yurtsev (PAF proposals and comments) and Tzvelev (2000a, 2000c, comments) accepted the northern plants as four species and some subspecies: R. acris s. str. which they stated to occur only as an anthropochore in northern European Russia and Siberia; R. subborealis with two subspecies, subsp. subborealis (= R. borealis auct.) and subsp. pumilus (= R. lanuginosiformis) in northern Europe and Siberia east to Yakutia; R. glabriusculus in northeastern European Russia and northwestern Siberia; and R. turneri in Siberia and Beringia from northern Yakutia east to northwestern Canada with two subspecies, the Siberian subsp. jacuticus and the amphi-Beringian subsp. turneri. Tzvelev (1994) renamed the main plant in northern European Russia and northwestern Siberia as R. subborealis because he considered Trautvetter's R. borealis (described from Kazakhstan) to be different and to be restricted to southern Siberia and central Asia.

Northwestern Europe. - Nurmi (2001) considered the aggregate a group of probably closely related, diploid, and interfertile subspecies and varieties within one species, R. acris, "Because the species is mainly an outbreeder, has a uniform chromosome number (2n = 14) but see Russian reports of 2n = 28 below, and is common throughout its range. There are no barriers preventing intraspecific gene flow. As a result the variation is mainly clinal. Several of the described taxa may therefore, alternatively, be regarded as parts of clines". This comment is relevant also outside the Nordic area as Nurmi's Nordic 'clines' include four of the taxa accepted as species by Russian authors: R. acris s. str., R. glabriusculus, R. pumilus (R. lanuginosiformis), and R. subborealis (R. borealis auct.). Northern Europe is a meeting place of much variation in this group. Nurmi assigned the variation among northern plants to four taxa: (a) subsp. acris (corresponding to the Russian usage of R. acris), the major temperate to boreal European and western Siberian race, mapped by him to reach the Arctic in Norway and possibly also in the Murman area and occasionally present as an anthropochore in, e.g., Bear Island, Spitsbergen, and probably Greenland; (b) subsp. borealis var. borealis, a northeastern European and northern Russian race, reaching the Arctic in Norway, Russia, and probably also Siberia (see Tolmachev 1971b), corresponding to the Russian usage of R. subborealis + R. glabriusculus + R. pumilus; (c) subsp. borealis var. pumilus, a geographically restricted alpine(-arctic) race in Fennoscandia and probably Iceland (different from the Hultén and Russian usage of the name "pumilus"); and (d) the oceanic subsp. borealis var. villosus, a race present in western and northwestern Europe and reaching the Arctic in Norway, Iceland, and Greenland (even if not stated as such by Nurmi). The last-mentioned race may reach northwestern European Russia but has probably not been considered by Russian authors. Nurmi's varieties of subsp. borealis are allopatric to parapatric and fairly widespread races. In addition, Nurmi commented on one or two more temperate races.

The Nordic plants were studied in preparation for Elven et al. (2005). The same taxa that Nurmi recognized were treated as four subspecies and the variation pattern was interpreted differently. We found R. acris s. str. to be fairly southern with few or no certainly native occurrences in the Arctic in Norway. It keeps distinct from the three other races accepted by Nurmi, whereas these show transitions wherever they co-occur. We have decided to accept these three as parapatric races of a species apart from R. acris: R. subborealis. Transitions are frequently between the alpine subsp. pumilus and the two boreals subsp. villosus and subsp. subborealis (Nurmi's R. acris subsp. borealis var. borealis), more rarely between the two boreals because the zone of overlap is small. Subsequently, northern Russian and North American plants have been compared. We have found it difficult to draw a clear line between R. subborealis s. str. and R. turneri subsp. jacuticus in northern Siberia and even more difficult between subsp. jacuticus and the Beringian subsp. turneri. An alternative would be to merge nearly all the native, northern plants from northeastern Norway east to the Yukon Territory into one huge species for which the priority species name would be R. turneri.

There is near consensus among the PAF collaborators about the taxa (except for R. glabriusculus) but not about their ranks and names. One plant is entered provisionally (R. glabriusculus).