Herb with horizontal, branched rhizome growing in open mats, often over several square meters. Aerial shoots erect, either with vegetative 'rosettes' only (in reality shortened shoots with 1—2 pairs of crowded leaves) or flowering stems. Stems 10—15(20) cm, erect, more or less densely pubescent with up to 1—2 mm long, articulate, white hairs mixed with short glandular hairs, and abundant, sessile, yellow glands.
Leaves opposite, those of vegetative shoots and the lowermost pairs on the flowering stems crowded at base, but flowering stems with 1—2 pairs of leaves farther up. Basal and lower stem leaves 3—5(7) × 1—2(2.5) cm, lanceolate or oblong, narrowing gradually at the base into an indistinct petiole and apically into an acute or acuminate apex, sparsely pubescent with very short (0.2—0.5 mm), articulate hairs with a bulbous widening at the base. Upper stem leaves less than half the size of the basal leaves.
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 per stem (very rarely 1—2 lateral ones in addition). Heads 2.5—4.5 cm broad. Involucrum of 1(2) rows of 12—16 phyllaries, 7—12 × 3—5 mm, lanceolate, acute, green at base and reddish or purplish at tip, with 1—2 mm long, articulate hairs. Receptacle convex, hairy. Flowers of two kinds. Marginal flowers 10—15, female, monosymmetric, corolla ligulate (all petals joined in ligula facing outwards). Ligulas 12—17 × 4—6 mm including claw ca. 5 mm, yellow or yellowish orange, apically with ca. 3 irregular teeth. Central flowers numerous, bisexual, radially symmetric, 4—6 mm, corolla tubular with 5 short, obtuse teeth, yellow. Sepals transformed to a pappus in both kinds of flowers.
Fruit pubescent with short, white hairs. Pappus hairs 8—12 mm, densely barbed to feathery.
Reproduction by seeds, probably asexual (agamospermy); local vegetative reproduction by rhizomes. The inflorescences and flowers are adapted to cross pollination (allogamy) by insects, with mechanisms making self-pollination (autogamy) nearly impossible. However, there may be little need of pollination as asexual seed set (agamospermy) predominates in Arnica (Wolf 2006). The chromosome numbers reported are several and partly irregular (2n = 38, 57, 76, 95, see Elven et al. 2011). Seed production is common in Svalbard but germination is poor, probably because of insufficient seed ripening (Alsos et al. 2013).
The fruits are adapted to wind dispersal, probably fairly efficient due to the feathery pappus.
There is nothing very similar to this species in Svalbard. The yellow-flowered species of Taraxacum differ in glabrous scapes without leaves and in dentate to lobed leaves, and also in only one type of flowers (ligulate ones) in the head.
Dry grassy heaths and meadows, cliff ledges and slopes with stable and luxuriant vegetation cover, in quite fine-grained substrates with circumneutral or basic soil reaction (pH). Arnica angustifolia is usually found in climatically favourable sites in the landscape, often associated with several other thermophilous plants.
Thermophilous. Confined to the middle arctic tundra zone and the clearly and weakly continental sections. The species is restricted to Spitsbergen but here it is rather frequent in the middle and inner fjord districts: Van Keulenfjorden (one site at Anna, Nathorst Land), Van Mijenfjorden (Nathorst and Nordenskiöld Lands), Isfjorden (Nordenskiöld, Dickson and James I Lands), Kongsfjorden (only Ossian Sarsfjellet, Haakon VII Land), Liefdefjorden (one site, Haakon VII Land), Wijdefjorden (Andrée Land and Ny-Friesland), and somewhat isolated on the northeast coast at Lomfjorden (Ny-Friesland).
The species is circumpolar in several races. The Svalbard race is western arctic, mainly in North America and Greenland but transgressing to Svalbard. See Comments.
The Svalbard material of Arnica angustifolia belongs to the western arctic ssp. angustifolia, otherwise known from Greenland, Canada and Alaska. To the east of Svalbard, it is replaced by the morphologically slightly but constantly different ssp. iljinii (Maguire) I.K.Ferguson in arctic Russia and Siberia, and by the geographically very restricted and also morphologically different ssp. alpina (L.) I.K.Ferguson (A. fennoscandica Jurtz. & Korobkov) in N Fennoscandia. These three races are parts of a circumpolar complex that has been revised several times (e.g., Maguire 1942, 1943; Douglas & Ruyle-Douglas 1978; Wolf 1980, 1987, 2006; Downie 1988) but still in need of a combined morphological, cytological and molecular investigation. Based on the available evidence (morphology), the dispersal connection of the Svalbard plants is most probably westwards to Greenland.
The name Arnica alpina (L.) Olin 1799 has often been applied to this species. It is based on A. montana L. var. alpina L. 1753, described on the N Fennoscandian plant (i.e., the current ssp. alpina), but at rank of species this name is inapplicable because it is predated by the name A. alpina Salisb. 1796 referring to a species of Doronicum (see Ferguson 1973).
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.
Douglas, G.W. & Ruyle-Douglas, G. 1978. Nomenclatural changes in the Asteraceae of British Columbia. 1. Senecioneae. – Canadian Journal of Botany 56: 1710–1711.
Downie, S.R. 1988. Morphological, cytological, and flavonoid variability of the Arnica angustifolia aggregate (Asteraceae). – Canadian Journal of Botany 66: 24–39.
Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/
Ferguson, I.K. 1973. (229) Arnica L. – In: Heywood, V.H. (ed.), Flora Europaea, Notulae systematicae, No. 14. – Botanical Journal of the Linnaean Society 67: 282.
Maguire, B. 1942. Arnica in Alaska and Yukon. – Madroño 6: 153–155.
Maguire, B. 1943. A monograph of the genus Arnica. – Brittonia 4: 386–510.
Wolf, S.J. 1980. Cytogeographical studies in the genus Arnica (Compositae: Senecioneae). I. – American Journal of Botany 67: 300–308.
Wolf, S.J. 1987. Cytotaxonomic studies in the genus Arnica (Compositae: Senecioneae). – Rhodora 89: 391–400.
Wolf, S.J. 2006. Arnica Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 21. Magnoliophyta: Asteridae (in part): Asteraceae, part 3: 366–377.