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GROWTH FORM

Solitary herb, often in small tussocks with small lateral shoots from the vertical main caudex. These shoots may become independent of the mother plant but only at a very short distance (1 cm). Stems erect, to 12–15 cm, singly from each shoot, but up to 12 stems observed on one individual. Leaves crowded at the base and on the lower part of the stems. Stems, leaves, and phyllaries with long, articulate hairs.

LEAF

Leaves alternate. Basal leaves 4–5 cm, oblanceolate or narrowly oblanceolate, glabrous or sparsely pubescent, obtuse. Stem leaves 1–5 cm, linear or narrowly oblanceolate, acute, villous with white, shiny hairs.

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 head terminally on each stem. Involucrum rounded to truncate at base. Phyllaries in several rows, subappressed, 0.7–1 cm, lanceolate, pubescent with white, shiny articulate hairs; some hairs with purple cell walls may occur. Marginal flowers monosymmetric, female, with corolla ligulate (all petals fused into a ligula facing outwards, with ca. 3 indistinct teeth at apex), (4)5–6 mm, white or pale purple. Central flowers radially symmetric, bisexual with corolla tubular and yellow.

FRUIT

The fruit is an achene with pappus of numerous white, dentate hairs. Numerous fruits from each head.

REPRODUCTION

Sexual reproduction by seeds; no vegetative reproduction. Flowers are adapted to insect pollination and outcrossing. The local distribution, as a population rich in individuals, suggests that seed recruitment takes place regularly.

Fruits are adapted to wind dispersal due to their pappus but probably not for very long distances.

COMPARISON

The three species of Erigeron in Svalbard differ in several features: Erigeron eriocephalus is similar to E. uniflorus in that the hairs on the phyllaries and the upper parts of the stem are mostly white, but it is taller and has an involucrum broadly subglobular and with strongly spreading phyllaries; E. humilis is 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.

HABITAT

Only found on a single, steep scree slope with a southern exposure, together with the two other species of Erigeron. On open, base-rich gravel and loam. The site is close to the arctic steppe along Wijdefjorden but not within a steppe vegetation type.

DISTRIBUTION

The single known occurrence, in Ringhorndalen on the east side of Wijdefjorden (Ny-Friesland), was discovered in 2015 and is located in the middle arctic tundra zone and the clearly continental sector. The site is assumed to have locally high summer temperature due to high insolation and wind shelter.

The occurrence of Erigeron uniflorus is highly isolated, by 900−1000 km from the nearest known sites in N Norway and the Kola Peninsula. The general range is alpine in central and southern Europe, Fennoscandia and western Asia. See Comments..

COMMENTS

Erigeron uniflorus is closely related to, and at the same ploidy level (diploid) as the circumpolar E. eriocephalus. These two are often considered subspecies or varieties of one species (E. uniflorus s. lat.) due to transitional forms found in the Scandinavian mountains and perhaps in Iceland (e.g., Lid & Lid 2005; Nesom 2006). considered E. uniflorus s. str. to be restricted to the central European mountains, whereas they assigned all northern plants to their ssp. eriocephalus. This was obviously wrong as no difference has been found between Alpine and Scandinavian E. uniflorus but several differences between Scandinavian E. uniflorus and arctic E. eriocephalus. At a global scale, the two are rather different and the Scandinavian plants assigned to E. eriocephalus may be transitional. Ecologically, the two differ in Scandinavia. Erigeron eriocephalus is a plant of sunny, dry sites; E. uniflorus a plant of moist snowbeds. However, in Svalbard they grow closely together in the single known site of E. uniflorus.

LITERATURE

Hultén, E. & Fries, M. 1986. Atlas of North European Vascular Plants North of the Tropic of Cancer. – Königstein: Koeltz Scientific Books.

Lid, J. & Lid, D.T. 2005. Norsk flora. Ed. 7 by R. Elven. – Det Norske Samlaget, Oslo.

Nesom, G.L. 2006. Erigeron Linnaeus. – In: Flora of North America Editorial Committee, eds., Flora of North America north of Mexico. 20. Magnoliophyta: Asteridae (in part): Asteraceae, part 2: 256–348.

PHOTOS Erigeron uniflorus

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Observations in svalbard

__Herbarium specimen __Observation

ALL SPECIES OF THE GENUS Erigeron