Panarctic Flora

910601-03 The Bupleurum triradiatum aggregate B. americanum, B. arcticum, B. triradiatum

2n= (1) 8 (2x, x = 4). - Siberia. - Rostovtseva (1976, for B. triradiatum).
(2) 12 (2x, x = 6). - Siberia, Far East. - Gurzenkov and Gorovoy (1971); Vassiljeva et al. (1992). Both for B. triradiatum.
(3) 14 (2x, x = 7). - Alaska. - Johnson and Packer (1968).
(4) 16 (2x, x = 8, and/or 4x, x = 4). - Siberia (N, S), Far East (N). - Numerous reports, mostly for B. triradiatum.
(5) 28 32 (4x, x = 7 and 8). - Alaska. - Packer and McPherson (1974).
The base chromosome numbers seem to be diverse. In addition, assignment of counts to taxa has been difficult. Inspection of vouchers is needed in almost every case.

Geography: Asian (C-NE) - amphi-Beringian - Cordilleran.

Notes: Murray and Elven: Bupleurum reaches the Arctic in the broadly amphi-Pacific/Beringian regions either with a single polymorphic taxon or a group of probably closely related taxa. These have been proposed treated in two ways. Tikhomirov (1980, PAF proposal) and Pimenov (1996) included all arctic plants in one species, B. triradiatum. Krasnoborov (1998) considered B. triradiatum s. str. to be non-arctic and assigned the northern plants to three other species: B. ajanense with a subsp. ajanense in the non-arctic parts of northeastern Asia and in Alaska where it reaches the Arctic, and a subsp. purpureum in the southern Rockies; B. arcticum in northeastern Asia and Alaska, in both regions reaching the Arctic; and B. sibiricum with a subsp. sibiricum in southern Siberia and the Russian Far East, perhaps reaching the Arctic in northeastern Yakutia, and a subsp. americanum widespread in northwestern North America and also present on the Chukchi Peninsula.

We differ from Tikhomirov, Pimenov, and many previous and current American authors in finding the variation too disjunct to be included in a single species as mostly done on both the Russian (as B. triradiatum) and the American side (as B. americanum). Based on a survey of material (ALA, O), we can agree with major parts of Krasnoborov's treatment but we want to propose some changes indicated in the treatment below where we accept three taxa (as species) from the Arctic. We propose that also B. triradiatum s. str. should be considered in an arctic context. We are less convinced that B. ajanense and B. sibiricum should be treated as specifically distinct. The B. triradiatum group should be investigated combining morphology, cytology, and molecules, as also indicated by the complexity in chromosome numbers.