Panarctic Flora

641039 Potentilla arenosa (Turcz.) Juz.

• Juz., Fl. URSS 10: 137 (1941). - Potentilla nivea var. arenosa Turcz., Bull. Soc. Imp. Naturalistes Moscou 16: 607 (1843). Described from the Transbaikal area (Siberia).

Geography: Circumboreal-polar.

Notes: Elven and Murray: Potentilla arenosa s. lat. is characterized by a predominance on petioles and stems, and often on other parts, of long, patent, straight, and distinctly verrucose hairs (strong lense). Floccose hairs are absent. The lower leaf surfaces have short crispate hairs and mostly long straight hairs. The upper leaf surfaces are glabrous, subglabrous, or with scattered short or sometimes long, stiff hairs. Other hair types may also occur, especially on the petioles a dense understorey of very short, straight, stiff hairs in subsp. arenosa or very short curved hairs in var. nipharga. The leaves are predominantly ternate with the terminal leaflet distinctly stalked or at least narrowly cuneate at base, and leaflets are deeply dissected with often acute teeth. Circumscribed in this way, P. arenosa s. lat. becomes well delimited from P. nivea s. lat. and P. crebridens s. lat., from the P. uniflora aggregate, and from the diverse plants with digitate, semidigitate, or semipinnate leaves.

Yurtsev: The northern Siberian populations of [P. arenosa s. str.] morphologically approaches P. arenosa subsp. chamissonis. In northeastern Asia including Chukotka occur plants with deeply dissected 5-foliolate leaves resembling the type of P. hookeriana in their appearence. They were described as P. arenosa var. pinnatisecta. According to Eriksen and Yurtsev (1999), the taxa form a quite natural group with wool on the lower side of leaves and verrucose straight to flexuose hairs on petioles and veins, the middle (terminal) leaflet usually petiolulate. Characteristic for many populations are also short conical styles viscid-verrucose in their lower 1/3-1/2.

As was established by Juzepczuk, Hultén, and A.E. Porsild, the only important diagnostic character separating subsp. arenosa from subsp. chamissonis (=? P. kuznetzowii) is the pubescence of petioles with an upper layer of long stiff patent (spreading) hairs and a lower layer of short stiff bristles, normally also patent ones. In var. nipharga they are short, but incurved. Various authors (including Hultén) have noted that the lower layer is absent in subsp. chamissonis, despite it is seen even on the photograph of the type in Hultén (1945b). In reality, in subsp. chamissonis is present on many petioles a lower layer of comparatively short, adpressed, somewhat flexuose hairs. In some leaves the lower layer of hair may be absent but the same is true also for subsp. arenosa.

My conclusion. I prefer treatment as two or three species. The major species (treated widely) should be called P. arenosa. As to the P. chamissonis-kuznetzowii problem, we should perhaps prefer the former name though the longitudinal taxonomical gradient in populations of P. chamissonis s. lat. should be studied in various ways. Until such study is made, it would be more safe to consider P. arenosa and P. chamissonis at species level.

Elven: Soják (in comment) rather considered P. chamissonis a hybrid species from P. arenosa s. str. x P. nivea. We have recently (2011) re-examined the holotype (S). The petioles have both long straight and short hairs, but there are no floccose hairs whatsoever. In addition, leaflet dissection, shape of teeth, the stalked terminal leaflet, and blade pubescence are in conflict with P. nivea. We see no reason to assign the name "chamissonis" to the hybrid as suggested by Soják.

Elven and Murray: We largely agree with Yurtsev but not as to rank of the taxa. In our opinion, the morphological differences between P. arenosa s. str. and P. chamissonis are small and intergrading. The intermediates mentioned by Yurtsev count against two species. We therefore go for two parapatric subspecies, at most.

We have compared Cordilleran and northern and western arctic American material (ALA, CAN, DAO, O) and assign all of it to subsp. arenosa. We have also compared with Russian subsp. arenosa and find the northern and northeastern Asian plants studied in the field to be indistinguishable from Alaskan and Canadian plants studied similarly. We enter subsp. arenosa as a nearly circumpolar race.

In spite of Yurtsev's and Soják's comments above, there is some difference between the amphi-Atlantic plants of subsp. chamissonis and those of subsp. arenosa but admittedly mostly in petiole pubescence: a lack or short hairs or more rarely a very sparse layer of short, soft hairs in subsp. chamissonis; a nearly uniform presence of a mostly dense layer of very short, stiff bristles in subsp. arenosa or of short, curved hairs in var. nipharga (we enter this taxon provisionally as a taxon nipharga). We therefore accept subsp. chamissonis as a second major race in the broadly amphi-Atlantic regions. The overlap is found in northern Canada where subsp. arenosa predominates in the north and west, subsp. chamissonis in the southeast, in Greenland where the former is northern, the latter southern, and probably in northeastern Russia and northwestern Siberia. Our conclusion is based on a study of much material from Scandinavia, Svalbard, Greenland, Canada, and Alaska but on a restricted Russian material.