Betula spp. (bet’-ewe-la)
Family: Betulaceae, Birch
Key Steps
- 1b – Alternate leaf arrangement — go to 18
- 18a – Leaf simple — go to 19
- 19b – Thornless — go to 22
- 22d – All leaves lobed — go to 23
- 19b – Thornless — go to 22
- 18a – Leaf simple — go to 19
Description
Leaf: Doubly toothed. Triangular, diamond-shaped or egg-shaped, depending on species. Blunt base. Generally, no glands on petiole.
Bud: Long, pointed, may be twisted. Some may be divergent (sticking out away from the stem). On second year’s growth, the lateral buds may be on very short branches, giving the bud the appearance of being stalked. Two or four exposed, overlapping bud scales, the lower scales are very short. True terminal bud absent.
Leaf Scar: Semi-oval, crescent-shaped, small. Three bundle scars but they are very hard to see.
Stem: New stems are reddish-brown, slender, may be heavily lenticelled and hairy. On second year stems, leaves arranged in pairs on short spur-like branches.
Bark: Older bark separates into thin, papery sheets. May be creamy white or brown.
Pith: Small, round, solid.
Flower: Two types of “catkins” may be present on the same tree. Male: long, slender and drooping, near end of stem. Female: shorter, fat, erect, like a miniature, papery cone. April to June.
Fruit: Cone-shaped strobiles, shattering when ripe. Scales are 3-lobed or unlobed, thin and papery.
Habit: Medium sized ornamental. Shape varies with species. 15 to 30 feet tall.
Culture: Medium to high moisture requirement.
River Birch, B. nigra — Leaves: broad, wedged base, smooth margin at base, rest is doubly toothed or may even be slightly lobed, 7-9 pairs of veins. 1/2 inch long petiole. Buds hug the stem and may be hairy. Reddish, peeling bark.
Paper or Canoe Birch, B. papyrifera — Leaf base is round or heart-shaped and smooth. Rest of margin is coarsely and doubly toothed. Leaf has pointed tip. Small, warty, black glands (bumps) along main veins. Smooth above, usually hairy beneath at angles of the veins. 6-10 pairs of veins. 1 inch long petiole. Buds stick out away from the stem. Hairy bud scale margins. Bark white, papery. Young stems reddish-brown.
Cutleaf Weeping Birch, B. pendula ‘Gracilis’ — Leaf shape is lobed, deeply cut. Bark is white, peeling, papery. Pendulous branching pattern. Prone to borer damage, attacks top center of tree first. Avoid south and west exposures. Prefers cool and moist conditions.
Rocky Mountain Birch, B. occidentalis — 20 feet by 15 feet, upright clump. Moist conditions.
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