Sweet Birch is a medium sized long-lived North American aromatic deciduous tree with a straight trunk and a rounded crown of spreading branches, growing to 60 feet high. Twigs and foliage have the odor of wintergreen when crushed. The sap is plentiful and useful - see notes below.
The bark is reddish-brown to black with horizontal lenticels on young trees, smooth but not papery, becoming gray to almost black on older stems and fissuring into large, thin irregular scaly plates.
Twigs are slender, smooth, reddish-brown in color with small lenticels. Terminal buds are usually lacking; lateral buds are reddish-brown with green margins on the scales, sharply pointed.
The leaves are alternate, elliptical with long pointed tips and a notched (slightly cordate) base leading to a short stalk. The margins are usually doubly saw-toothed, 2 to 4 inches long. The veins are prominent with a midvein and 9 to 13 distinct laterals on either side. The upper surface is shiny green, the underside paler with hair only on the leaf stalk. Fall color is bright yellow.
Flowers: The tree is monoecious, that is with separate male and female flowers. Male flowers (staminate) occur in a cluster of 3 to 6 reddish-green aments (catkins), that appear on the twigs in the fall of the previous year and then elongate in the spring, up to 3 - 4 inches long, near the ends of twigs, in hanging clusters taking on a yellow-purple color. The individual flowers are only 1/8 inch long, are yellowish with 2 stamens, a 4-lobed calyx and are in groups of 3 and somewhat obscured by small bracts. Female flowers (pistillate) appear with the leaves and are reddish-green upright aments (catkins), about 3/4 to 1-1/4 inches long at maturity, back of the tip on the same twigs. They have an ovary, a pair of styles but no calyx or petals and occur in closely associated groups of 3 and are also obscured by bracts. Catkins are also referred to as 'aments'.
Fruit: Pollination is by wind. Flowers mature to a short-stalked upright cylindrical non-woody cone-like structure, 3/4 to 1-1/4 inches long, brownish in color with many 3-lobed scales (without hair) containing 2-winged nutlets, the wings narrower that than the nutlet, which mature in the fall and disperse by wind and water in the winter and following spring. These cone-like structures will usually remain on the twig after seed release. Seeds are not produced on young trees but some seed is produced by 20 years of age with heavy seed production between 40 and 70 years of age.
Habitat: Sweet Birch grows in moist uplands with other hardwoods but will tolerate dry soils. It does best in rich slightly acidic well drained soil.
Names: The common names refer to various characteristics of the tree, 'black' for the bark, 'sweet' for the sap and 'cherry' for the bark and leaves of young branches which can be mistaken for a cherry tree. The name 'birch' itself is derived from an old Teutonic word. The genus, Betula, is the Latin word for the birch tree. The species lenta, means 'tough' as is the wood of this species. The author name for the plant classification, 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. In the 19th Century the tree was commonly known as the Black Birch with other names used more regionally. Francois Michaux in North American Sylva of 1819-21 (Ref. #26c) reports that 'Sweet' and 'Cherry' were commonly used in Connecticut, Massachusetts and farther north, while in Canada 'Cherry' was universally used. The River Birch, B. nigra, is also sometimes called 'Black Birch', but that name more appropriately applies here.
Comparisons: The Yellow Birch, B. alleghaniensis has some similar characteristics to this species - leaves that have a rounded to heart shaped base and 8+ pairs of lateral veins on the leaf. But Yellow Birch has bark that is a yellowish-gray and the scales of its cones have hair on the margins. Other birches have leaves not usually rounded or heart-shaped at the base and have fewer than 8 lateral veins, and the scales of the cones fall away quickly rather than persist into winter. For a leaf comparison see the photo below.
Above: 1st photo - Sweet Birch has a rounded crown with spreading branches. 2nd photo - Bark on older trunks is gray to blackish and fissures into scaly plates. 3rd photo - Bark on younger stems has reddish-brown tones with horizontal lenticels; not papery.
Below: 1st photo - Twigs are reddish-brown with small white lenticels; lateral buds are reddish-brown with green margins to the scales; sharply pointed. 2nd photo - Leaves are elliptical, with double-sawtoothed margins, pointed tips, slightly cordate base, resembling the leaf of the cherry tree.
Below: 1st photo - The male catkins form in the fall at the ends of twigs in clusters of 3 to 6. Then (2nd & 3rd photos) they elongate in Spring, perfecting their flowers for pollination. In the second photo - note the developing female catkins just back from the tip where the male catkins are.
Below: Flowers are in the catkins. 1st photo - The female catkin is upright and reddish-green when first formed. The reddish styles diminish after fertilization (2nd photo). The female catkins are placed back from the tip of the same twig where the male catkins occur.
1st photo - Female catkins develop into a green cone shape, that then (2nd photo) matures to a brown scaly cone containing numerous 3-lobed scales. When the cone breaks apart, (3rd photo) these are scattered by the wind, over winter and the following spring as the cone remains on the tree overwinter. 4th photo - The three-lobed scales contain two winged nutlets (left and right of the central lobe).
Below: A twig with typical leaf arrangement and a female catkin near the tip of the twig; the tip with the male catkins has broken off.
Below: A comparison of leaves of the five Birch species described on this site.
Notes: Sweet Birch is not native to Minnesota but grows well here in the proper environment. Eloise Butler was familiar with the tree from her native Maine and she planted it in the Garden in 1910 with plants obtained from Kelsey's Nursery on the East Coast. Martha Crone did not list the species on her 1951 Garden Census, but Gardener Cary George reported replanting the tree in 1994. Sweet Birch grows in a rather restricted area from southern Maine west to the southernmost part of Ontario and then south into the Appalachian Mountains to northern Georgia.
Eight species of birch are recorded from surveys in Minnesota. Three of them are crosses formerly reported but there are no known populations. The other five are native and are: B. alleghaniensis, Yellow Birch; B. cordifolia, Heart-leaved Birch; B. nigra, River Birch; B. papyrifera, Paper Birch; and B. pumila, Bog Birch. All but B. cordifolia are in the Garden.
Uses: From the leaves, twigs, bark and the wood of young Sweet Birch, Oil of Wintergreen or Birch Oil, was once extracted in great quantities. It was used to flavor medicines and candy. The Yellow Birch also produces this oil, but in less quantity per tree than the Sweet Birch. This has been replaced by a manufacturing process that creates the oil from wood alcohol and salicylic acid. The second major use of the tree was to tap the sap, just like a Sugar Maple. The sap flows a month later than the Maple, but in greater quantity and faster. It is boiled just like the Maple but is stronger - like molasses. Birch beer was frequently made from the sap of Sweet Birch. (Ref. #6 & below).
Botanist Francois Michaux (son of Andre) wrote in his North American Sylva of 1819-21 (Ref.#26c): "The agreeable foliage of this species, and the valuable properties of its wood, render it the most interesting of the American Birches. The wood of the Black Birch, when freshly cut, is of a rosy hue, which deepens by exposure to the light. Its grain is fine and close, whence it is susceptible to a brilliant polish; it possesses also a considerable share of strength. Tables and bedsteads of this wood, when carefully preserved, acquire with time the appearance of Mahogany; hence it is employed in Boston for the frames of arm-chairs and sofas: coach-makers also use if for the frames of their panels."
Birch Beer: "To every gallon whereof, add a pound of refined sugar, and boyl it about a quarter or half an hour; then set it to cool, and add a very little yeast to it, and it will ferment, and thereby purge it self from that little dross the liquor and sugar can yield: then put in in a barrel, and add thereto a small proportion of cinnamon and mace bruised, about half an ounce of both to ten gallons; then stop it very close, and about a month after bottle it; and in a few days you will have a most delicate brisk wine of a flavor like unto rhenish. Its spirits are so volatile, that they are apt to break the bottles, unless placed in a Refrigeratory, and when poured out, it gives a white head in the glass. This liquor is not of long duration, unless preserved very cool." Vinetum Britannicum, John Worlidge, London, England 1678
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"