Panarctic Flora

641038 Potentilla drymeja Soják

• Soják, Folia Geobot. Phytotax. 5: 111 (1970). Holotype (PR): Mongolia: "in declivibus inter pagos Baga-Tenger et Zajsan ad marginem borealem montium Bogd-ul in vicinitate australi urbis Ulan-Bator", 22. July 1965, leg. Deyl and Soják.
• Potentilla tomentulosa Jurtz., Fl. Arct. URSS 9, 1: 318, 174 (1984). Holotype (LE): Russian Far East: West Chukotka, "montium Tschukotensium, pars centralis, ad ripam sinistram fl. Alarmagtyn (systema fl. Kuekvun)", 14. Aug. 1965, leg. B. Yurtsev and V. Petrovsky 298.

2n= (1) 42 (6x). - Far East (West Chukotka). - Zhukova and Petrovsky (1985b, one count in the holotype of P. tomentulosa).
(2) 70 (10x). - Far East (West Chukotka). - Zhukova and Petrovsky (1985b, one count).

Geography: Asian (N) - amphi-Beringian: RUS SIB RFE ALA.

Notes: Soják (2004) synonymized Potentilla tomentulosa Jurtz. 1984 with P. drymeja Soják 1970 which he interpreted to be a hybrid species from P. arenosa subsp. arenosa x P. crebridens subsp. hemicryophila.

Yurtsev: A member of the following series of forms: P. crebridens - P. nivea (subsp. mischkinii) - P. drymeja - P. [arenosa subsp.] chamissonis - P. arenosa (var. nipharga) - P. arenosa s. str. It is a puzzling problem, however, whether this series reflects the real sequence of transformations and the role of hybridization in them. Anyway, in some groups (including Potentilla and Dryas) hybridization supports taxonomical continuum independently of whether you like or dislike it, despite inconvenience for taxonomical classification.

Potentilla drymeja matches P. arenosa in general appearance - including veins on the lower surface of leaflets not covered with wool - but the lower layer of its hairs contains short subappressed wool which proved to be mostly crispate. But essentially, P. drymeja has a mixture of hairs, e.g., according to Eriksen and Yurtsev (1999), both on the lower surface of leaf blades and on petioles and stems is a mixture of short crispate and floccose hairs. As well as on petioles and leaf veins in the same species there is mixture of verrucose and smooth straight hairs. The same is also the case in P. petrovskyi and P. anachoretica var. planiuscula (evidence of hybrid origin?). Numerous small glands on veins in P. drymeja differentiate it from both presumed parents.

Elven and Murray: Plants intermediate between P. nivea and P. crebridens (subsp. hemicryophila) one one side and P. arenosa subsp. arenosa and subsp. chamissonis on the other are frequent within the largely overlapping ranges of their assumed parents. Whether such intermediates should be considered as up to three hybrid species (from "arenosa" s. str. x "nivea", "arenosa" s. str. x "crebridens" [P. drymeja, P. tomentulosa], and "chamissonis" x "nivea" [P. prostrata, P. mischkinii, P. subquinata]) or just as occasional hybridogeneous biotypes is a matter of principle. The parental species may be so closely related that back-crossing prevents stabilization of hybrid species. We accept that the hybrids form populations locally but are more in doubt whether these populations collectively are justifiable as independent species.

Yurtsev reported P. drymeja (as P. tomentulosa) from localities scattered from the Urals east to western Alaska, partly as frequent. In our opinion, P. drymeja represents a variable hybridization situation with occasional establishment of agamic biotypes forming populations. These are mostly not accepted as taxa by North American or northwestern European authors. It is also a matter of concern that this hybrid, which involves in the assumed parentage the Beringian P. crebridens subsp. hemicryophila, is reported by Yurtsev as far west as the northern Urals. It is therefore probable that also P. nivea, and perhaps P. arenosa subsp. chamissonis, are involved in the taxon as considered by Yurtsev. In the northern European and North American material, we do not find the same consistency in these proposed taxa as in other proposed hybrid species.