Figure 1.

Black cottonwood floral morphology. Images are digitized. A, Mature black cottonwood trees on a riverbank during winter in Corvallis, Oregon. B, Developing inflorescence and vegetative buds in early summer. C, Developing inflorescence bud in early summer. Bud scales and the adjacent leaf petiole were removed. D, Mature female catkin in early spring. E, Mature male catkins in early spring. F, Mature female flower in early spring. G, Mature male flower in early spring. a, Axillary accessory inflorescence bud; f, filament of stamen; i, developing inflorescence; l, lateral axillary inflorescence bud; p, perianth cup; pt, petiole attachment (petiole removed); t, stamen; si, stigma; v, vegetative bud.