Panarctic Flora

Browse

670601 Transberingia bursifolia (DC.) Al-Shehbaz & O'Kane

Distribution

Taimyr - Severnaya Zemlya: Presence uncertain
Kharaulakh: Persistent (Adventive)
Yana - Kolyma: Scattered
West Chukotka: Rare
East Chukotka: Rare
Western Alaska: Rare
Northern Alaska - Yukon: Rare
Central Canada: Scattered
Ellesmere Island: Rare
Western Greenland: Scattered
Northern arctic Tundra: Rare
Mid Arctic Tundra: Rare
Southern Arcti Tundra: Scattered
Shrub Tundra: Scattered
Bordering boreal or alpine areas: Rare

2n= (1) 16 (2x). - Far East (N), Alaska, Canada (NW), Greenland. - Several reports, three from East Chukotka specified for "tschuktschorum".
(2) 20. - Alaska. - Dawe and Murray (1981a). Probably an aneuploid number.

Geography: Asian (NE) - amphi-Beringian - North American (N): SIB RFE ALA CAN GRL.

Notes: Yurtsev: I accept two species, one with two varieties. My arguments are that these plants are continental, essentially subarctic plants with a ruderal strategy. Their range is disjunct and the local populations usually poor in individuals. There is a large gap between the ranges in Asia ("bursifolia" s. str.) and North America ("mollis"), between the isthmus of the Chukchi Peninsula and the lower Mackenzie River, but the plants on the two sides differ only in a few characters, e.g., shape of cells in the mechanical tissue of the inner walls of valves (almost round in "mollis", multiangular in "bursifolia") according to Velichkin. The plants compared are from Kolyma in northeastern Asia and Greenland and it is not known whether these distinctions are stable in the areas between. At the present stage of knowledge, I find it more safe to unite both in one species.

Approximately at the center of the gap between the Chukchi Peninsula isthmus and the Mackenzie River, two very small and strongly isolated populations have been discovered, deviating much even from a rather variable Arabidopsis bursifolia. The distinction of one of them corresponds to the rank of variety, whereas that of the other corresponds to the rank of species. The situation could be explained in terms of gene drift in very small populations under marginal climatic conditions. I think that the gap was brought about by the Holocene humidification of climate following upon shelf flooding in central Beringia. I have proposed one of the populations as Arabidopsis tschuktschorum, the other as Arabidopsis bursifolia var. beringensis. For Arabidopsis tschuktschorum, the following characters: besides a number of distinctive features in the habit (e.g., ascendent-prostrate floriferous stems with wider obtusate leaves with or without very short auricles, infloresence of numerous congested flowers, polycarpic life cycle, thicker rugose taproot), the plant differs from Arabidopsis bursifolia s. lat. in sepals persistent (not caducous), densely pubescent with minute ramose hairs, siliques widest above the middle part, septum with one wide perforation and one distinct marginal median vein. For var. beringensis, the following characters were given as compared with the type variety: smaller size of many parts and their numbers, siliques more abruptly (not gradually) angustate towards both base and apex, and seeds ellipsoid (not oblong).

Murray and Elven: Price et al. (2001) inspected a fair amount of material and recognized two subspecies, a Cordilleran subsp. virgata (Nutt. ex Torr. & A. Gray) R.A. Price, Al-Shehbaz & O'Kane and a widely amphi-Beringian, North American, and Greenlandic subsp. bursifolia which included the plants named as "mollis", "tschuktschorum", and "beringensis" (without recombinations of names within Transberingia or Beringia). These authors probably saw no material of the two single-population taxa proposed by Yurtsev but have based their conclusions on the descriptions and on the general variability of the species. We are reluctant to accept taxa based on single populations, especially in a case like this when the populations appear in a gap within the distribution of one species. We share Yurtsev's hypothesis about the causes of the divergence (inbreeding in very small populations) but not his taxonomic conclusions. We consider Yurtsev's species and variety part of the inter-populational variation in T. bursifolia.

Higher Taxa