630602-06 The Oxytropis nigrescens aggregate O. bryophila, O. czukotica, O. gorodkovii, O. kokrinensis, O. nigrescens
Geography: Asian (N) - amphi-Beringian.
Notes: Elven, Murray, and Yurtsev: This intricate group has been handled in three different ways:
(a) The majority of North American authors from Barneby (1952) to Welsh (2001) and Gillett et al. (2007) have included all North American plants of the aggregate (and also Oxytropis arctobia) within one species: O. nigrescens with varieties.
(b) Hultén (1968b) described the northwestern North American variation as three subspecies of O. nigrescens (implying Asian subsp. nigrescens to be a fourth) and commented: "Their limitation between themselves is sometimes obscure and their status as species, subspecies or varieties is open to discussion. These taxa are therefore regarded as races, interfertile where they meet, not as species". Hultén accepted, however, O. kokrinensis and O. arctobia.
(c) Yurtsev (1986, PAF proposal) accepted all the taxa at rank of species. His arguments (in comments) are based, among other things, on morphological distinctions, i.e., independent series of "oligomerization" (reduction in number of, e.g., leaflets and flowers) from at least two ancestral diploids, O. nigrescens s. str. and O. pumilio or their progenitors, on co-occurrence of distinct taxa where they overlap (i.e., no transitions), and on ploidy differences. The species proposed by Yurtsev are diploid and/or tetraploid and most of them have parapatric ranges: O. nigrescens s. str. from the Jenisei to the Kolyma River, O. czukotica from the Kolyma River to the Bering Strait areas, O. gorodkovii ("pygmaea") in the Bering Strait areas and eastwards, and O. bryophila mainly in Alaska and the Yukon Territory.
There are no experimental studies supporting any of the views. Hultén's supposition of hybridization and transitions is not supported by any evidence and is contrary to our (Elven, Murray, Yurtsev) field experiences. The difference between the views of Hultén and Yurtsev concerns both rank and biology: where Hultén saw intergrading races, Yurtsev saw closely related and geographically overlapping but non-intergrading species.
None of us support a racial approach, neither the Hultén subspecies not the American varietal proposal. We accept specific rank for the taxa based on Yurtsev's supposition of several lineages leading up to the present-day complex, the variation in ploidy level, the large degree of parapatry, the morphological distinctness of the taxa where they overlap or even grow intermixed (as we have observed in many sites in both Alaska and Chukotka), and the lack of documentation of any hybridization or intergradation. We have at present no factual support for treating these plants as anything else than species, except that they have several characters in common.
- Oxytropis [6306,genus]