|
Northern Ontario Plant Database
Plant DescriptionBetula papyrifera MarshallEn: white birch, paper birch, canoe birch
Betulaceae (Birch Family) Click on thumbnail to see larger image.
General: A medium-sized hardwood tree, to 25 m tall, with spreading to ascending branches. Bark reddish brown with light lenticels when young, white and horizontally peeling (exfoliating) in papery shreds or sheets when mature; inner bark pinkish to orange. Twigs hairy (pubescent) and often glandular, lacking a wintergreen flavour when chewed; lenticels prominent, horizontal, becoming dark brown to black in maturity; buds somewhat resinous. Terminal bud lacking on long twigs; lateral buds 5-7 mm long, blunt-tipped, with 3 two-toned scales, greenish toward the base and brown at the tip. Short spur shoots have terminal buds with 5-7 scales. Leaves: Alternate, simple, pinnately-veined, with 9 or fewer pairs of veins, petiolate. Leaf blade ovate to broadly ovate, 5-9 cm long, 4-7 cm wide, widest near the base; upper surface dull, lower surface paler. Young leaves are pubescent beneath and often retain hairs along the veins and in the vein axils when mature. Leaf apex pointed to sharply pointed (acute to acuminate); base rounded; margins double serrate. Flowers: Unisexual, with male and female flowers occurring on the same trees (monoecious). Male flowers occur in pendulous catkins, 1-3 cm long at first, expanding to 9-10 cm long when pollen is shed. Male catkins are located near the branch tips while female catkins are positioned farther back on the twig. Each scale of the male catkin is associated with 3 male flowers, each with 2-3 stamens. Female flowers occur in erect catkins, 1-2 cm long. Pistillate scales subtend 2-3 female flowers, each composed of a single of a pistil with a 2-carpelled, inferior ovary and 2 pinkish to reddish stigmas. Flowers bloom in spring with the emerging leaves. Fruits: The pendant fruiting catkins are cylindrical, 2.5-5 cm long, to 1.5 cm wide, with many small bracts (pistillate scales), 2-3 mm long, subtending the small dry fruits, which are winged nutlets, 1.5-2.5 mm long. The 3-lobed pistillate scales have a narrow base with 2 rounded, lateral lobes that diverge nearly perpendicular to the short pointed central lobe. The thin, papery wings of the fruit are much wider than the nutlet. Fruits mature in late summer. Habitat and Range: White birch occurs in northern temperate, mixedwood, and boreal forests of northern U.S. and Canada. It is shade intolerant, so occurs mainly as a successional species, establishing quickly in disturbed or harvested forest sites. The range of white birch extends throughout Ontario, except for the coastal tundra of Hudson Bay. It occurs in a wide variety of soil and stand types. Internet Links: The Betula papyrifera website from the USDA Silvics of North America website. The Betula papyrifera webpage from the Trees of Wisconsin website. Similar Species: White birch can be distinguised from yellow birch (Betula alleghaniensis) by the latter's yellowish to silvery-gray bark, which peels off in small, thin curls. Yellow birch twigs have a wintergreen flavour when chewed, while white birch twigs have no flavour. The pistillate fruiting scales of the yellow and paper birch also differ. Yellow birch has scales with the ascending lateral lobes and central lobe of similar size, whereas paper birch has a central lobe that is pointed and smaller than its 2 divergent lateral lobes. The leaves of white birch may also be confused with Ostrya virginiana (ironwood) leaves. However, the inflated involucres surrounding the small nutlets of ironwood easily differentiate the two plants. Ostrya twigs also lacks spur shoots, which are characteristic of birch species, and has buds with several scales. – written by Derek Goertz and S.J. Meades Back to species list |
||||||||||||||||||||||
Last Modified: