Solitary or weakly mat-forming herb with a single white tap root and a darkish brown vertical caudex, more or less branched apically into a crown covered by blackish brown marcescent leaf remains. Each caudex branch ending in a rosette at ground level with 5–8(10) leaves. Leaf rosettes with 0–5 hollow scapes usually 3–10 cm long and 2–4 mm thick. Scapes pink or red, characteristically curved downwards and transversally wrinkled in bud and fruit stage, often also in flowering stage. The entire plant is glabrous.
Leaves 5–10 × 1–1.5 cm, with a winged petiole 1/3–1/4 of entire leaf length. Blade oblanceolate to spathulate in outline, broadest in the distal 1/3, with 2–4 pairs of distant, shallow to deep, retrorse lobes (a runcinate leaf), end lobe usually narrowly triangular and obtuse, green or dark green with a broad pale mid vein.
INFLORESCENCE AND FLOWER
The primary inflorescence of Asteraceae is a head (capitulum) surrounded by an involucrum of one or more rows of phyllaries (involucral bracts). The flowers sit on a flat, concave or convex receptacle, sometimes with scales (the bracts of the single flowers). The flowers are epigynous with perianth at top of the gynoecium. The sepals are always transformed into a pappus, mostly by hairs or sometimes by scales. The 5 stamens are inserted in the corolla tube and the anthers form a ring through which the style grows and pushes the pollen outwards. Gynoecium of two fused carpels, 2 stigmas. The fruit is an achene with one seed.
Inflorescence a single apical head 1.5–2.0 cm broad. Involucrum of 2 rows of black or blackish green phyllaries without appendages (horns). Outer phyllaries 8–10, 3–5 × 3–5 mm, about half as long as inner phyllaries, appressed, broadly triangular or obcordate with a slightly extended obtuse apex. Inner phyllaries 5–12, 8–12 × 1.5–2 mm, appressed, narrowly oblong, the inner ones with a broad hyaline margin. Receptacle flat, without scales. Flowers monosymmetric. Corollas ligulate (above the corolla tube all petals are fused in a long ligula facing outwards), ligulas 20–30, 10–15 mm, ending in (3)5 short, irregular teeth, white or cream, with a broad lilac stripe on the outer surface.
The fruit is divided into a body, a narrowly cylindrical beak with a conical thickening at the base (the cone), and a pappus as a stalked, feathery umbrella on the fruit. Fruit body 4–6 × 0.7–0.9 mm, shiny blackish brown with shallow ribs and with obscure teeth in the apical part, cone insignificant, beak 2.5–4 mm, pappus rays ca. 4 mm, white and obscurely dentate.
Asexual reproduction by seeds; very local vegetative reproduction by fragmentation of rhizome. Nearly all species of Taraxacum (and there are thousands, more than 1200 described from Europe alone) are agamospermous, i.e., with seed development independent of fertilization. Pollen may be well developed (yellow) or not (green or blackish green) but is assumed non-functional in nearly all species. Among the boreal and arctic species, sexual reproduction is suspected in only one species: the west arctic T. holmenianum Sahlin with a diploid chromosome number (2n = 16). Taraxacum arcticum is pentaploid (2n = 40). Flowering and seed set is usually abundant. Seeds germinated to 55 % in an experiment (Alsos et al. 2013).
Fruits are easily spread by wind due to their umbrella-like pappus.
The runcinate leaves and the scabose heads with only ligulate flowers are unique for the genus Taraxacum in Svalbard. Taraxacum arcticum is readily recognized from the other species of the genus in the area by its small heads with white or nearly white flowers (the others have larger heads with deep yellow flowers), the curved and wrinkled scapes, the short, appressed and nearly black phyllaries (the others have dark green and much longer phyllaries, the outer ones often spreading to reflexed), and the small and very dark fruits with no or a few short teeth and beaks not longer than the fruit body.
Moist heaths and meadows, often on slopes with some snow protection in winter (early snowbeds), sometimes in bird manured sites. Probably indifferent as to soil reaction (pH).
Rather frequent in the fjord districts in the middle and northern arctic tundra zone and in all sections. The majority of sites are on Spitsbergen but with some in NW Nordaustlandet and a very few in Edgeøya and Barentsøya. Not known from Bjørnøya.
Taraxacum arcticum is mainly a Eurasian arctic species, reaching from Svalbard east to the Chukchi Peninsula in NE Asia, but also reported to occur in N Greenland (confirmation perhaps needed). The connection of the Svalbard plants is obviously to the east to arctic Russia.
The section to which this species belongs was previously named sect. Arctica but currently sect. Antarctica, due to the inclusion of species in southernmost South America; i.e., the section is bipolar. This is one of the two major sections of Taraxacum in the Arctic (the other being sect. Borealia, previously Ceratophora, see Elven et al. 2011 for a survey) but it is very sparsely represented in W Europe: one species in Svalbard (T. arcticum), one in S–C Norway (T. dovrense), and two in the E Alps (T. handelii and T. reichenbachii). The major parts of the diversity of this section are found in Russia, Siberia, and North America, including Greenland where at least 3 species occur in the northern parts. Whereas T. arcticum in Svalbard is a regular part of the arctic vegetation pattern, the other species of the section in Norway and the Alps seem to be glacial relicts and are very rare.
Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.
Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/