Flowers opening in spring with or after the leaves; stamens 4; pistillate aments inclosed during the winter; wing of the nut broad; leaves ovate, sinuately lobed, lustrous on the lower surface. 1. A. sinuata (B, F, G). Flowers opening in winter or early spring before the unfolding of the leaves; pistillate aments usually naked during the winter. Wing of the nut broad; leaves ovate or elliptic, rusty-pubescent on the lower surface; pistillate aments often inclosed during the winter; stamens 4. 2. A. rubra (B, G). Wing of the nut reduced to a narrow border. Stamens 4; leaves oblong-ovate, glabrous or puberulous on the lower surface. 3. A. tenuifolia (B, F, G). Stamens usually 2, or 3. Leaves ovate or oval. 4. A. rhombifolia (B, F, G). Leaves oblong-lanceolate, acute. 5. A. oblongifolia (H). Flowers opening in autumn from aments of the year; stamens 4; wing of the nut reduced to a narrow border; leaves oblong-ovate or obovate, dark green and lustrous above, pale yellow-green below. 6. A. maritima (A). 1. Alnus sinuata Rydb. Alder. _Alnus sitchensis_ Sarg. [Illustration: Fig. 209]