Betula cordifolia (Heart-leaved Birch)
|Also known as:||Mountain White Birch|
|Life cycle:||perennial woody|
|Habitat:||part shade, sun; moist; rocky slopes, hardwood forest|
|Plant height:||50 to 80 feet|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Male and female flowers are borne separately on the same tree (monoecious), in clusters called catkins. Male catkins are in groups of 1 to 3 at tips of 1 year old twigs, pendulous in flower, 2 to 4¼ inches long, developing in fall as a slender spike of tightly appressed scales and opening up the following spring. Female catkins are erect and stout, cylindrical, 1/3 to ½ inch long from new, spur-like lateral twigs on the same branch as the males.
Leaves and bark:
Leaves are alternate and simple in 2s or 3s on short, spur-like lateral twigs, and singly on the new, elongating terminal branchlets. The blade is generally egg-shaped, 2 to 4¼ inches long, 1¼ to 2¾ inches wide, pointed at the tip, heart-shaped at the base, on a 1/3 to 1 inch, hairy stalk. Edges are double-toothed, the upper surface dark green and sparsely hairy becoming smooth, the lower surface lighter green with hairs on veins and with tufts in vein axils. Leaves have 9 to 12 pairs of lateral veins.
Twigs are brown to reddish brown with scattered lenticels (pores), new growth is hairy becoming mostly hairless and shiny the second year. Bark is thin and smooth, whitish with shades of gray and pink, older bark can peel into wide horizontal strips or often remaining smooth to the base of the trunk. Trunks can reach 30 inches diameter at breast height (dbh), though more commonly 16 to 20 inches.
Female catkins become nodding to pendulous, cylindrical clusters, 1½ to 2¼ inches long, of winged nutlets each around 1/8 inch long, green drying to brown.
Heart-leaved Birch is not only similar to the more familiar Paper Birch (Betula papyrifera), until recently many (if not most) references have treated it as a variety of that species (var. cordifolia). But not only are there genetic distinctions, B. cordifolia is much more restricted in range to the extreme northeastern Arrowhead region. And not only are its leaves the characteristic heart-shape that gives it its common name, these leaves typically have more veins (9 to 12 pairs vs. 9 or fewer). Its bark, while white and papery, is thinner and less chalky than Paper Birch, almost shiny, staying smooth to the base of the trunk, and the inner bark is often a dark, cherry pink compared to the lighter reddish tan of Paper Birch.
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Photos courtesy Peter M. Dziuk taken in Cook and Lake counties.
Have you seen this plant in Minnesota, or have any other comments about it?