Betula nana L.
Arctic dwarf birch, bouleau nain.
Betulaceae, birch family.
Sp. Pl. 2: 983. 1753
Vegetative morphology. Plants shrubs; 10–30 cm high (on Arctic islands); with branched or unbranched matted stems that lack warty glands. Aerial stems decumbent, or prostrate; covered with few inconspicuous sessile glands; densely hairy. Branches grey-brown, or brownish (differentiated into short and long shoots); glabrescent, or hairy (sparsely to densely so, seen at 10X). Branchlets grey-brown; hairy (at the tips of twigs). Leaves distributed along the stems; alternate (2-ranked); existing for a single season or less (deciduous). Petioles 0.5–2 mm long; glabrous, or hairy (sparsely). Leaf blade bases obtuse, or acute. Juvenile leaves glabrous. Blades 8–15 mm long; 6–10(–20) mm wide. Blades obovate (broadly orbiculate); flat; veins pinnate (with 2–6 pairs of prominent lateral veins). Blades secondary veins arising along midrib (and branching). Blades adaxial surface glabrous. Blades abaxial surface glabrous, or hairy (sparsely; occasionally with a few small resinous glands). Blade margins not lobed (considered deeply crenate). Blade margins crenate (deeply so); with teeth toward the apex; with teeth per cm 2–8. Leaf apices obtuse, or rounded.
Reproductive morphology. Plants monoecious. Flowering stems present. Flowering stems with leaves (on short shoots). Inflorescence a catkin; dense; cylindrical (erect). Pedicels absent. Catkins flowering with the opening of leaf buds (the catkins are produced the season before flowering but retained in buds during winter). Female catkins densely flowered; 5–15 mm long; 3.5–4.5(–10) mm wide; subglobose; peduncles 1–3 mm long; borne on a flowering branchlet. Staminate flowers inconspicuous (staminate catkins mostly terminal on branchlets, rarely preserved). Floral bracts green (with red tips, turning brown with age, central lobe elongate, rarely preserved in herbarium specimens); widest toward tip; 0.5–1.5(–2.5) mm long; 0.8–2 mm wide; apex obtuse. Perianth absent. Flowers unisexual. Gynoecia inferior. Carpels syncarpous; 2. Styles 2; free. Ovules 1. Fruit dry; a samara (broadest near the centre, with definite wings that are much narrower than the body and not extended beyond it at the apex). Fruit information not found. Seeds 1.
Chromosome information. 2n = 28. For the collective species: 28 (4x). - Zhukova et al. (1973 north eastern Asia); Krogulevich (1976 northern Siberia). Ploidy levels recorded 4x.
Distribution. Northern hemisphere distribution: Greenland and Canada (and local). Nunavut Islands. Low arctic. Range in the Canadian Arctic Archipelago limited. Arctic Islands: Baffin.
Ecology and habitat. Substrates: tundra; rocks (barrens).
Notes. Furlow (1997) distinguishes subsp. nana as having young
twigs pubescent, not covered with conspicuous resinous layer. This is the taxon
that occurs in the eastern Canadian Arctic Archipelago. Plant with twigs
glabrous or only puberulent, and covered with a thick resinous coating are B.
nana subsp. exilis (Sukaczev) Hultén. This subspecies occurs
in the Yukon, Alaska and Northern Asia.
Betula nana subsp.
nana occurs in both eastern and western Greenland at latitudes north of
63 degrees. Inorthern Europe, the range of this subspecies extends across the
subarctic zone and southward in the Alps and other ranges.
There seems to be
some agreement that there are three major geographic races, the very widely
amphi-Atlantic subsp. nana, the Russian-Siberian subsp. tundrarum
and the widely amphi-Beringian subsp. exilis (Elven et al. 2002).
Illustrations. • Plant habitat. Plant growing in mine tailings. Most of the leaves are turning colour in the fall. Norway, Roros. Aiken, s.n. • Close-up of stem. Centre: catkin. Note stems without conspicuous glands. Norway, Roros. Aiken s.n. • Arctic Island Distribution.
Cite this publication as: ‘S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, L.J. Gillespie, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, A.K. Brysting and H. Solstad. 1999 onwards. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 29th April 2003. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980) and Dallwitz, Paine and Zurcher (1993, 1995, 2000) should also be cited (see References).
