Aspen
It is a hardy species which tolerates long, cold winters and short summers. Aspen is dioecious, so individual trees are either male or female (in contrast to most trees, where male and female flowers occur on the same tree). Trees flower in March and April, before the leaves appear, with both the male and female trees producing catkins. Pollinated female catkins ripen in early summer and release tiny seeds which are tufted with hairs.