Betula nigra L., synonym Betula rubra Michx. Black Birch, River Birch or Red Birch Native to the eastern United States, where it grows in wet ground near rivers. Cultivated as an ornamental in northern states. Height to 24-27m (80-90ft), usually with the trunk split low down into 2 or 3 stems. Flowers open in late April, male catkins 5-7.5cm (2-3in) long, females 0·8cm (1/3in). Fruiting catkins are downy, 2.5-3.7cm (1-1½in) long, erect and have short stems. They ripen and break up early in the year in June. This allows seeds to germinate on river banks, when the water level is at its lowest. Leaves are doubly toothed, almost lobed and downy on veins underneath. Bark is distinctly dark and flaking. Z4.