Panarctic Flora

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500706 Saxifraga oppositifolia L.

2n= (1) 26 (2x). - Europe (C, N, Svalbard), Russia (N), Canada (W, N), Greenland. - Numerous reports.
(2) 39 (3x). - Greenland. - Jørgensen et al. (1958, counted together with two diploid plants).
(3) ca. 48 52 56 (4x). - Europe (Svalbard), Far East (N), Alaska, Canada (Southampton Island). - Numerous reports.
Not included: Löve and Löve (1951, 1956b) reported both 2x and 4x from Iceland but Löve (1970a) and Löve and Löve (1975a) reported only diploids from there.

Geography: Circumpolar-alpine.

Notes: Zhmylev: Saxifraga oppositifolia is a circumpolar arctic-alpine species with considerable variation in habit, cilia length and hydatode number on the leaves, shape and pubescence of sepals, and size and colour of petals. The geographical pattern of this morphological polymorphism is not clear. The majority of botanists therefore accept a broad interpretation of S. oppositifolia. Two subspecies are proposed: a widely distributed subsp. oppositifolia and a broadly amphi-Beringian subsp. smalliana.

Elven: Two ploidy levels are represented by 2n = 26 and 52, functionally diploid and tetraploid, with a few deviating numbers. Diploids are reported throughout except for Beringia, whereas tetraploids are documented from Beringia (numerous reports and counts), northern Canada (one), and Svalbard (two).

Several attempts have been made to subdivide this species, also in an arctic context. In a very extensive investigation of molecular markers throughout the range, Abbott and collaborators (Abbott et al. 2000; Holderegger and Abbott 2003; Abbott and Comes 2004) found two major groups of genotypes, one centered in Beringia and North America and another centered in the North Atlantic regions, Europe, and western Siberia. These two major lineages may be represented taxonomically as two races (subspecies). Zones of overlap were found especially in Greenland and in northern Siberia around Taimyr. Saxifraga oppositifolia was described from "Spitzbergensium, Lapponicarum, Pyrenaicarum, Helveticarum" (i.e., Svalbard, northern Scandinavia, southwestern and central Europe) and the Linnaean type most probably belongs to the mainland European diploid race. There are two proposals for the possibly Beringian and North American, predominantly tetraploid race:

(1) Hultén (1968a, 1968b) recognized some northwestern North American plants as subsp. smalliana (Engl. & Irmsch.) Hultén based on S. pulvinata Small. These are characterized by pulvinate growth, densely imbricate leaves with very few or no cilia, and distinctly elongating pedicels in fruit stage. Saxifraga pulvinata was described from an area (the Yukon Territory) where tetraploids prevail, where almost all populations have glandular hairs on the sepals (see below), and where the Beringian-American genotypes of Abbott et al. (2000) are almost exclusive. Hultén (1968a) mapped this race from the American side only but it is also recognized from the Asian side. According to Zhmylev (PAF proposal), the limit between subsp. smalliana and subsp. oppositifolia in northern Asia is comparatively sharp and runs more or less along the Kolyma River between Chukotka and Yakutia. This is supported by field experiences (2004-2005, Elven and Solstad) where inspected plants in northern Yakutia morphologically fell into the oppositifolia category and those in Chukotka into the smalliana category.

The pulvinate growth form is, however, not an adequate diagnostic character for this race. Pulvinate plants are found throughout the arctic and northern alpine regions, often in exposed sites, whereas a trailing growth form predominates in more sheltered sites close by. In some areas, like Svalbard where two taxa have been proposed (Rønning 1996), it is modificative and without genetic support (Brysting et al. 1996). The investigated (pulvinate) Svalbard plants have (mostly) eglandular sepals and short pedicels. Both pulvinate and trailing plants occur also in the Beringian areas but there both kinds have glandular sepals and long pedicels.

(2) Hultén (1973) took notice of the geographical pattern in glandular sepals. He described subsp. glandulisepala to be a broadly amphi-Beringian race from northeastern Asia east to Greenland. He considered S. smalliana to be a different, narrowly Beringian and Cordilleran race (see maps in Hultén and Fries 1986). As this character has not been analysed in the same way on the Russian side, Zhmylev's concept of subsp. smalliana is the same as Hultén's of subsp. glandulisepala but different from Hultén's of subsp. smalliana. Zhmylev commented that his subsp. smalliana differs from the type subspecies in glandular hairs on the sepals, absence of leaves in upper part of the stem and platycampaniform calyx. He stated that transitions occur in regions where both subspecies are present and that S. czekanowskii Sipliv. probably is such a transitional form.

Aiken and Elven: We looked at North American and North Atlantic material (ALA, CAN, DAO, O) and found that almost all specimens in Beringian and northern Cordilleran America and in the westernmost Canadian islands (Banks, Victoria) had glandular sepals. Glands on sepals became increasingly rare eastwards throughout arctic Canada, and only a few specimens in northern Greenland and a very few in Svalbard showed these. The transition was gradual. Morphologically, we found this too little to recognize subspecies as there seem to be few other associated characters, but the morphological pattern largely corresponds with the genotype pattern of Abbott et al. (2000). The correlation between these subspecies and the two main ploidy levels is uncertain but the majority of diploids belong to subsp. oppositifolia (except in the Rocky Mountains), whereas the majority of tetraploids belong to subsp. smalliana (the main discrepancy being the Svalbard tetraploids where the vouchers, if there are any, have not been studied morphologically).

Elven, Aiken, Murray, and Zhmylev: Based on these considerations, we accept two races of S. oppositifolia: one amphi-Atlantic and Siberian and one amphi-Beringian and North American. The former is subsp. oppositifolia. The latter we treat as subsp. smalliana because Small's pulvinata (on which S. smalliana is based) by us is considered a modification or ecotype of the broader race, and the name has priority before the morphologically more descriptive name subsp. glandulisepala. This solution finds some support in the results of Abbott and Comes (2004) and was adopted for Flora of North America by Brouillet and Elvander (2009b).

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