River Birch is a forked, slightly leaning tree with an irregular crown. It grows to 80 feet in height.
The bark is smooth, ranging from creamy-white to shiny silver-ish to pinkish-brown and irregularly peeling into papery scales. The underside of the peeling layer is tinted red. With time, the bark becomes thick, fissured and shaggy with dark horizontal expanded lenticels.
Twigs are slender and very supple, reddish-brown and smooth to slightly hairy. Buds are slender and may be slightly hairy. There is no odor or taste of wintergreen when twigs are cut like there is with Yellow Birch.
Leaves are alternate, simple, ovate to almost 4-sided, about 1 to 3 inches long, with double saw-toothed edges, a stalked wedge shape base, shiny green on top and pale and fuzzy below, or at least on the mid-vein and there are often small resinous glands. Leaf stalks are hairy. Larger leaves will usually be shallowly lobed. There are usually 5 to 12 pairs of lateral veins. Dull yellow color in autumn.
Flowers: The tree is monoecious, that is with separate male and female flowers. Male flowers (staminate) occur in a cluster of 2 to 3 reddish-green hanging catkins, that appear near the ends of twigs in the fall and then elongate in the spring, up to 3 inches long. The individual flowers are only 1/8 inch long, are yellowish with 2 stamens, a 4-lobed calyx and are somewhat obscured by small bracts. Female flowers (pistillate) appear with the leaves and are greenish upright catkins, about 3/4 to 1-1/4 inches long, back from the tip on the same twigs as the male flowers, usually. They have an ovary, a pair of styles but no calyx or petals. Flowers are in groups of three, obscured by a bract. Catkins are also referred to as 'aments'.
Fruit: Pollination is by wind. Female flowers mature to a short-stalked upright cylindrical non-woody cone, brownish in color with many hairy 3-lobed scales. The bracts have become dry scales at maturity, each scale having three hairy 2-winged seeds (or nutlets) attached which disperse by wind and water in early summer to the following Spring. In moist soils the seeds germinate quickly. Young trees do not form seeds. Seeds are about 375,000 per pound.
Habitat: River Birch grows near water sources in moist rich soil, poorly drained or well drained. It has adapted to landscape plantings far from water and grows well if adequate moisture is provided. Full sun is necessary - it is not shade tolerant. It does not spread from its root crown, but will re-sprout from a stump. This species is sometimes subject to an anthracnose leaf blight.
Names: The genus, Betula, is the Latin word for the birch tree. The species, nigra, is the Latin word for 'black', and refers to the almost black color of old bark and therein begins a confusion in the common names. In the 19th century the species was sometimes named Betula rubra, which matches the alternate common name of 'Red Birch' and refers to the reddist tint of the exfoliating bark. The other alternate name of 'Black Birch' should not be applied as it is more appropriately used for the Sweet Birch, B. lenta, as it was in the 19th Century. Therefore, 'River Birch' has become accepted, which kind of agrees with the older name 'Water Birch', which was applied due to the affinity of the species to riparian habitats. The name 'birch' itself is derived from an old Teutonic word. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: The bark of River Birch exfoliates in a manner different from Paper Birch where the texture is more uniform and the exfoliation is a strip to a sheet. Also, the bark of Paper Birch, B. papyrifera, is whitish without the dark furrowing of older bark. See below for a leaf comparison.
Above: Various shapes of the trees: 1st & 2nd photos - with a trunk branching from the base; 3rd photo - - single trunk with branching above.
Below: Bark ranges from creamy-white to shiny silver-ish to pinkish-brown and irregularly peeling into papery scales. With time, the bark becomes thick, fissured and shaggy.
Below: 1st photo - Twigs are slender, reddish-brown and smooth to slightly hairy. Buds are slender and may be slightly hairy. 2nd photo - Leaf undersides are fuzzy with hair on the stalk and usually on the mid-vein.
Below: 1st photo - The upper side is a shiny green; note the double saw-toothed edges and stalked wedge shape base. 2nd photo - Fall leaf color.
Below: Flower development: 1st photo - The hanging male catkins begin to elongate in early spring before the leaves. 2nd photo - The individual developed flowers are very small and obscured by small leafy bracts.
Below: 1st photo - The female catkin is upright on a twig and its flowers are also obscured by bracts. 2nd photo - The mature seed cone. Seeds are hairy 2-winged nutlets, scales are the 3-lobed parts.
Below: 1st photo - Male catkins form in the fall at the end of twigs and overwinter. 2nd photo - Female catkins in a typical arrangement on a twig. After pollination the male catkins have withered and dropped away.
Below: A comparison of leaves of the five Birch species described on this site.
Notes: River Birch is not indigenous to the Garden area. Martha Crone noted planting two of them on August 8, 1940 and presumably, those are the two large specimens found in marsh area of the Garden today. Ken Avery added a few in 1977. In North America River Birch is found only in the United States, in the eastern half of the country, all the way to the gulf coast. It is the southernmost New World Birch. In Minnesota it is native only to 4 counties - Washington, Wabasha, Winona and Houston. It has however, been extensively planted as a landscape ornamental in many areas as it grows well and can be long-lived with adequate moisture. 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. allegheniensis, 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: River Birch is not used for better quality lumber and veneers as it very knotty. It is however, tough, strong and close-grained and useful for small things and fuel.
Botanist Francois Michaux (son of Andre) wrote in his North American Sylva of 1841: "The epidermis of this species, like that of the Canoe Birch [B. papyrifera], divides itself transversely into thin, transparent sheets, which appear to be composed of a mixed substance, instead of presenting a pure, homogenous texture; hence they have not a uniform transparency nor a perfectly even surface: compared with the bark of the Canoe Birch, they are like coarse paper compared with fine. . . . In Philadelphia its twigs are exclusively chosen for the brooms with which the streets and court-yards are swept, which are similar to those employed for the same purpose in Paris. The twigs of the other species of Birch, being less supple and more brittle, are not proper for this use."
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.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"