Life span

Perennial, moderately long-lived.

Growth form

Solitary herb, sometimes in small tussocks, producing small lateral shoots from the vertical, main caudex. These shoots may become independent of the mother plant but at a very close distance (ca. 1 cm). Stems erect, very short before flowering, often < 1 cm, lengthening appreciably during and after flowering to 10–15 cm or more, singly from each shoot but up to 10 stems observed on one individual. Leaves crowded at the base and on the lower part of the stems. Stems, leaves and phyllaries (bracts) with long, articulate hairs.

Leaf

Leaves alternate. Basal leaves up to 3–4 cm, narrowly spathulate or oblanceolate, subglabrous or sparsely pubescent with white articulate hairs. Several stem leaves (4–6), much narrower and smaller than basal leaves, subacute or acute, sparsely pubescent.

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 terminally on each stem, Involucrum up to 2 cm broad, cuneate at base and tapering to stem. Phyllaries mainly in one row, appressed to head, 0.7–1 cm, lanceolate, strongly pubescent with articulate hairs with dark violet dividing walls. Marginal flowers monosymmetric, female with corolla ligulate (all petals fused into a ligula facing outwards, with ca. 3 indistinct teeth at apex), 4–6 mm and reaching 2–4 mm beyond phyllaries, white or more rarely pale purple. Central flowers radially symmetric, bisexual with corolla tubular and yellow.

Fruit

Fruit an achene (nut) with pappus of white, dentate hairs. Numerous fruits from each head.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers are adapted to insect pollination and outcrossing but we assume pollination between flowers within a head to be frequent. Flowering and fruit-set is regular. Seeds germinate to 40–50 % at about 20°C, but they did not germinate in a field study (Alsos et al. 2013, Müller et al. 2011).

Fruits are adapted to wind dispersal due to their pappus.

Comparison

The two species of Erigeron in Svalbard differ in several features: Erigeron humilis is much more short-grown, has an involucrum more narrowly cuneate with appressed phyllaries, and the hairs on the phyllaries and the upper parts of the stem are purple-walled; E. eriocephalus is taller, has an involucrum broadly subglobular and with strongly spreading phyllaries, and the hairs on the phyllaries and the upper parts of the stem are mostly white.

Habitat

Most common in snowbeds and heaths with snow protection in winter, usually growing in favourable aspects. Occurring on substrates with circumneutral to basic soil reaction (pH), usually moderately drained with fine textured soils. Probably absent from the areas with the most acidic substrates.

Distribution

Weakly thermophilous. Frequent in the middle arctic tundra zone, barely transgressing into the northern arctic tundra zone. Mainly in the clearly and weakly continental sections, barely transgressing into the transitional section. Confined to the fjord areas on Spitsbergen where it is rather frequent, and with one documented occurrence on W Edgeøya.

The general range is mainly American and Greenlandic, transgressing across the North Atlantic to Iceland, N Scandinavia and Svalbard (amphi-Atlantic) and across the Bering Straits to NE Asia (amphi-Beringian), see Elven et al. (2011). The connections of the Svalbard plants are to the south (Scandinavia) or west (Greenland).

Comments

Erigeron humilis is tetraploid (2n = 36) and reproductively isolated from its assumed close relatives E. uniflorus (mainland Europe and Iceland) and E. eriocephalus (circumarctic), both diploids (2n = 18). Seed-sterile triploid hybrids between E. humilis and E. uniflorus are reported from Scandinavia (Engelskjøn 1967).

Literature

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.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).

Engelskjøn, T. 1967. Contribution to the cytotaxonomy of Erigeron humilis Grah., E. uniflorus L., and their hybrid. – Nytt Magasin for Botanikk 14: 77–85.

Müller, E., Cooper, E.J. & Alsos, I.G. 2011. Germinability of arctic plants is high in perceived optimal conditions but low in the field. – Botany 89: 337–348.