Life span

Perennial, moderately long-lived.

Growth form

Mat-forming herb with extensively branched rhizomes, forming loose to dense stands up to 50 cm or more in diameter. Rhizome branches slender (0.5–1.5 mm broad), pale, with reduced leaves and buds at the nodes. Aerial shoots procumbent or ascending. Flowering stems 3–5(10) cm, with several pairs of leaves. The entire plant is glabrous.

Leaf

Leaves opposite, 0.5–1.5 × 0.3–1.0 cm, without distinct sheaths or petioles, broadly oblong, subacute with a small, blunt to apiculate point, fleshy, yellowish green; lamina with moderately distinct mid vein and two less distinct lateral veins. Dead leaves sometimes persist and become skeletal (with margins and veins retained but lamina rotting away), especially when buried in sand or gravel.

Inflorescence

Flowers singly or more rarely 2–3 together in a dichasial cyme at end of shoots, subsessile or very short-stalked (up to 5 mm).

Flower

Flowers radially symmetric, with 5 free sepals and petals. Sepals 2.5–4.0 × 1.4–1.7 mm, oblong, subacute or short apiculate, green or purplish. Petals about the same length as sepals, 2–4 × 0.8–1.2 mm, spathulate (with a narrow claw), entire, white. Stamens 10. Gynoecium of 3 (or 5) carpels, with 3 (or 5) styles.

Fruit

Fruit a spherical, one-roomed capsule, 5–8 × 5–8 mm, opening apically with 3 (or rarely 5) teeth, with numerous seeds. Seeds 3–4 mm brown, with verrucose surface.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowering is intermittent in Svalbard. However, the flowers have a honey smell and probably attract insects. Insect pollination may occur. The seeds germinate to only 4 % in an experiment (Alsos et al. 2013); however, we assume that some stratification (rough handling) is needed to break dormancy in this species.

The seeds float and are efficiently dispersed with sea currents.

Comparison

There is nothing similar to this species in Svalbard.

Habitat

Sandy and gravelly seashores, usually on very washed out (nutrient-poor) substrates but probably receiving some nutrients from drift material deposited on the shores by waves in summer and by sea ice in winter. Also occuring on gravelly road verges within the Longyearbyen settlement, probably brought with sand and gravel from the shore used for road maintenance.

Distribution

Honckenya peploides occurs in four areas on Spitsbergen: Agardbukta on the southeast coast (Sabine Land), near and within Longyearbyen and eastwards on the southern coast of Isfjorden towards Vindodden (Nordenskiöld Land), at Kongsfjorden northwest of Ny-Ålesund (Oscar II Land), and at Breibogen on the north coast (Haakon VII Land). This very disjunct appearance vouches for accidental dispersal, perhaps with all or the majority of the Svalbard locality groups recruited independently from outside Svalbard by sea current dispersal. It has also been reported from Bjørnøya but Engelskjøn & Schweitzer (1970) did not accept this record. Flowering has not been recorded in most of the Svalbard populations, and in the entire herbarium material, there is not one single mature or emptied fruit.

Outside Svalbard, this is the single race of this widespread species in the Arctic, recorded from several parts of arctic Russia, Siberia, Alaska, Canada, and Greenland, i.e., circumpolar.

Comments

Honckenya peploides is the single species of its genus, related to Minuartia but more closely related to the narrowly Beringian genus Wilhelmsia. It is polymorphic and has been divided on four races (subspecies, see Elven et al. 2011): ssp. diffusa throughout the arctic parts, ssp. peploides in non-arctic Atlantic Europe (north to Nordland in N Norway), ssp. robusta (Fernald) Hultén in non-arctic Atlantic North America, and ssp. major (Hook.) Hultén in Pacific North America north to Alaska and slightly penetrating the Arctic.

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. 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).

Engelskjøn, T. & Schweitzer, H.J. 1970. Studies on the flora of Bear Island (Bjørnøya). I. Vascular plants. – Astarte 3: 1–36.