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Life span

Perennial, but probably not long-lived.

Growth form

Solitary herb with a basal caudex sometimes covered with some leaf remains, mainly sheaths and mid veins, from previous seasons, branching into comparatively few, small, densely to loosely clustered rosettes forming small tussocks. Each rosette potentially with one flowering stem, up to 10 stems per tussock. Flowering stems erect, sometimes short at the beginning of the flowering, 1–2 cm, but elongating during and after flowering to 5–15 cm, glabrous, often red-tinged, and often with one leaf (besides occasional bracts).

Leaf

Leaf rosettes mostly 2–3 cm but occasionally up to 10 cm broad. Leaves alternate, up to 14 × 2 mm, entire, narrowly oblanceolate to nearly linear, acute, mid vein very prominent and raised, pale green. Both leaf surfaces glabrous or rarely with sparse long, stout, simple and forked hairs; margins with long, stout, simple and sometimes forked hairs, rarely glabrous. Hairs on leaf surfaces and margins pointing strongly forward.

Inflorescence

Inflorescence a raceme with 3–10(15) flowers, elongating in the fruit stage to 2–3.5 cm. Pedicels 2–6 mm, less than half the fruit length, slender, attached to the scape at an angle of 40–60° but regularly curved upwards, glabrous.

Flower

Flowers radially symmetric, with 4 free sepals and petals. Sepals up to 2 × 1 mm (i.e., twice as long as broad), green or tinged red with conspicuous white margins. Petals 2–2.5 × 1–1.5 mm, usually less than twice as long as sepals, not contiguous, erectopatent (making the flower half-open), broadly spathulate, notched, white.

Fruit

Fruit a silicule 4–7 × 1.5–2 mm, erect, elliptic or rarely lanceolate, glabrous, pale or dark green, sometimes strongly tinged purplish or reddish. Style short, up to 0.3 mm. Seeds 7–10 in each room, dark brown, ca. 1 × 0.75 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers are very small and highly selfing (Brochmann 1993). Flowering and seed-set is regular in most years; mature seeds are often observed. Grundt et al. (2006) found several sterility barriers between populations of Draba fladnizensis in the circumpolar area. Crosses between several populations from Svalbard and populations from South Norway and Alaska were included.

There are no special adaptations to seed dispersal.

Comparison

Draba fladnizensis is characterized by having only simple and sometimes forked, forward pointing hairs on the leaves, and glabrous stems and fruits. The only other white-flowered Draba in Svalbard with a predominance of simple hairs on the leaves (and glabrous stems and fruits), is D. lactea. This species, however, nearly always has some very small, multibranched hairs on the distal parts of the lower surface of leaves, and also much broader leaves with less strengthened mid vein, larger and broader petals (3.5–4 mm long vs. 2–2.5 mm), a more corymbose panicle, and fruits lanceolate or ovate rather than elliptic.

Habitat

Occurs in rocky, sparsely vegetated environments such as crevices and ledges, and on gravelly slopes and ridges. On well drained, dry or very dry substrates of mixed or coarse texture and with circumneutral to basic soil reaction (pH). The growth sites are usually exposed or semi-exposed, with little snow cover in winter and little competition. Little grazed by reindeer and geese.

Distribution

Thermophilous. Draba fladnizensis clearly has an affinity for sites with high insolation rates. It is restricted to the middle arctic tundra zone in the fjord regions, perhaps with 1–2 sites in the northern arctic tundra zone, and to the weakly and clearly continental sections, perhaps with 1–2 sites in the transitional section. Only known from Spitsbergen where it is rare, with localities scattered in the Isfjorden, Kongsfjorden, and Wijdefjorden districts and with a single, isolated locality reported from Sørkapp Land. Not recorded from Bjørnøya.

The general range is circumpolar in the low arctic and in mountains in the boreal and temperate zones. This is one of the most widespread of all Draba species, reaching south to C Europe (described from Austria), the southernmost Rocky Mountains at the border to Mexico, and to the Himalayas.

Comments

Draba fladnizensis is a diploid (2n = 16) species. It is recognizable everywhere and monomorphic, so that no feature has been found to distinguish, e.g., European, Asian or American plants. However, Grundt et al. (2006) have shown that this morphologically and cytologically uniform species consists of several cryptic species separated by sterility barriers both within and between regions (e.g., within and between N Europe and Alaska).

Several authors concerned with the American plants have claimed transitions between D. fladnizensis and D. lactea to be common (e.g., Hultén 1945, 1968; Scoggan 1978). Such claims are unfounded; natural hybrids are unknown and artificial hybrids sterile. The claims are based on an erroneous morphological concept of the two species (much D. lactea has been misidentified as D. fladnizensis). Other authors have assumed the diploid D. fladnizensis to be parental, together with the diploid D. nivalis, in the predominantly hexaploid D. lactea (e.g., Knaben 1966). Also this claim seems to be unfounded and based on a provincial viewpoint that the hybridization behind the hexaploid D. lactea must have taken place among species present in the North Atlantic regions. Grundt et al. (2004) rather point towards an origin from a Beringian diploid and tetraploid (2n = 16, 32) species, D. palanderiana.

Even if D. fladnizensis is monomorphic, a few plants have been difficult to place within this global uniform pattern, among these two populations from inner Wijdefjorden on Spitsbergen, found in 2010. They have a leaf pubescence different from any D. fladnizensis inspected worldwide and are under investigation.

Literature

Brochmann, C. 1993. Reproductive strategies of diploid and polyploid populations of Arctic Draba (Brassicaceae). – Plant Systematics & Evolution 185: 55–83.

Grundt, H.H., Kjølner, S., Borgen, L., Rieseberg, L.H. & Brochmann, C. 2006. High biological species diversity in the arctic flora. – Proceedings of the National Academy of Sciences 103: 972–975.

Grundt, H.H., Popp, M., Brochmann, C. & Oxelman, B. 2004. Polyploid origins in a circumpolar complex in Draba (Brassicaceae) inferred from cloned nuclear DNA sequences and fingerprints. – Molecular and Phylogenetic Evolution 32: 695–710.

Hultén, E. 1945. Flora of Alaska and Yukon. V. Dicotyledoneae. Rhoeadales, Sarraceniales, Rosales I (Crassulaceae, Saxifragaceae). – Acta Universitas Lundensis, n. s., sect. 2, 41(1): 797–978.

Hultén, E. 1968. Comments on the flora of Alaska and Yukon. – Arkiv för Botanik, ser. 2, 7(1). 147 pp.

Knaben, G. 1966. Cytotaxonomical studies in some Draba species. – Botaniska Notiser 119: 427–444.

Scoggan, H.J. 1978. The Flora of Canada. 3. Dicotyledoneae (Saururaceae to Violaceae) (pp. 547–1115). – National Museum of Natural Sciences, National Museums of Canada, Ottawa.