|Natural range of Betula occidentalis|
Betula occidentalis (Water Birch, also known as Red Birch) is a species of birch native to western North America, in Canada from Yukon east to western Ontario and southwards, and in the United States from eastern Washington east to western North Dakota, and south to eastern California, northern Arizona and northern New Mexico, and southwestern Alaska. It typically occurs along streams in mountainous regions. It is the only native birch found at low altitudes in the SE United States.
It is a deciduous shrub or small tree growing to 10 metres (33 ft) high, usually with multiple trunks. The bark is dark red-brown to blackish, and smooth but not exfoliating. The twigs are glabrous or thinly hairy, and odorless when scraped. The leaves are alternate, ovate to rhombic, 1–7 cm long and 1–4.5 centimetres (0.39–1.77 in) broad, with a serrated margin and two to six pairs of veins, and a short petiole up to 1.5 centimetres (0.59 in) long. The flowers are wind-pollinated catkins 2–4 centimetres (0.79–1.57 in) long, the male catkins pendulous, the female catkins erect. The fruit is 2–3 centimetres (0.79–1.18 in) long and 8–15 millimetres (0.31–0.59 in) broad, composed of numerous tiny winged seeds packed between the catkin bracts.
It has a strong tendency to epicormic growth resulting in a habit of many small limbs sprouting from the trunk causing the wood to be full of small knots.
- Saliendra, NicanorZ.; Sperry, JohnS.; Comstock, JonathanP. (1995). "Influence of leaf water status on stomatal response to humidity, hydraulic conductance, and soil drought in Betula occidentalis". Planta 196 (2). doi:10.1007/BF00201396. ISSN 0032-0935.
- Sperry, J. S.; Pockman, W. T. (1993). "Limitation of transpiration by hydraulic conductance and xylem cavitation in Betula occidentalis". Plant, Cell and Environment 16 (3): 279–287. doi:10.1111/j.1365-3040.1993.tb00870.x. ISSN 0140-7791.
- Sperry, J. S.; Saliendra, N. Z. (1994). "Intra- and inter-plant variation in xylem cavitation in Betula occidentalis". Plant, Cell and Environment 17 (11): 1233–1241. doi:10.1111/j.1365-3040.1994.tb02021.x. ISSN 0140-7791.
- Sperry, John S (2000). "Hydraulic constraints on plant gas exchange". Agricultural and Forest Meteorology 104 (1): 13–23. doi:10.1016/S0168-1923(00)00144-1. ISSN 0168-1923.
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