Panarctic Flora

500729 Saxifraga cernua L.

• L., Sp. Pl.: 403 (1753). Lectotype (LINN): Sweden: "Lapland". Herb. Linn. 575.44 (Siplivinsky 1977: 108).

2n= 24-72. - Europe (N), Russia (N), Siberia (N), Far East (N), Alaska, Canada, Greenland. - Numerous reports.
Reports of comparatively low chromosome numbers (2n < 40) are concentrated to northeastern Russia and northwestern Siberia (the meeting zone with S. sibirica) and to the Russian Far East (the meeting zone with S. radiata). See notes for interpretation.

Geography: Circumpolar-alpine: ICE NOR RUS SIB RFE ALA CAN GRL.

Notes: Zhmylev: Saxifraga cernua is a circumpolar, arctic-alpine species propagating mainly by bulbils; probably a complex of two close species formed as a result of hybridization and polyploidy between pseudoviviparous races of S. radiata and S. sibirica.

Elven: The mainly high polyploid S. cernua seems to be heterogeneous and have in its parentage, besides S. rivularis, the non-arctic S. sibirica (diploid and low polyploid) in one of its parts and the boreal to arctic S. radiata (diploid and low polyploid) in another part. These two genetic parts are geographically overlapping: markers in common with S. sibirica occur more or less throughout, whereas markers in common with S. radiata occur mainly in Beringia but also to some degree east to northeastern Canada (Southampton and Baffin islands) and west at least to Taimyr, perhaps to Svalbard. Transitions between S. sibirica and S. cernua were analysed from the Urals (Kapralov et al. 2006, and in comment) and are interpreted as hybrids, and similar transitional forms between S. radiata and S. cernua have been collected (2003-2005) and substantiated by molecular markers (AFLP) from northern Siberia, Chukotka, western and northern Alaska, and northern Canada (Elven and Solstad etc., ALA, O). They are included in an ongoing molecular and morphological study by Gabrielsen et al. (unpubl.). Jørgensen and Elven studied the material in LE in 2003 and found much additional evidence of transitional forms between S. cernua and S. sibirica throughout the non-arctic parts of Siberia and between S. cernua and S. radiata in northeastern Siberia and the Russian Far East. The transitional plants generally have fewer bulbils than S. cernua but more branches and flowers and are also intermediate in petal size and leaf shape. Transitional forms towards S. sibirica are without runners, those towards S. radiata mostly with runners. It is probable that S. cernua is a complex hybrid species, or a set of species, with at least both the two mentioned diploid and low polyploid species in its parentage, in addition to member(s) of the S. rivularis aggregate. A third putative candidate for parentage of parts of S. cernua is the Cordilleran S. debilis.

Molecular evidence (Gabrielsen et al. unpubl.) supports that one or more taxa of the S. rivularis aggregate partake in the parentage of S. cernua together with both S. radiata and S. sibirica. It is probable that transitions between the two diploid and low polyploid species (S. radiata and S. sibirica) and S. cernua are frequent. We have not seen pseudoviviparous plants of S. sibirica or S. radiata and assume the pseudovivipary to be restricted to the hybridogenous offspring.

Seed reproduction occurs in S. cernua, although only as a very small proportion of the total reproduction (see Gabrielsen and Brochmann 1998 and references therein).