Many broad-leaved trees are deciduous. This means that they shed their leaves at certain times of the year. In the tropics, deciduous trees shed their leaves at the start of the dry season. In temperate regions, as days grow shorter and colder, the chlorophyll, which makes leaves green, breaks down. Scar tissue and sometimes a material called wound gum grows across the base of each leaf stalk, and eventually the leaf drops off.
Evergreen trees keep many of their leaves all year round.
Each leaf lasts up to four years and often has a dark, waxy skin. Some trees, such as horse chestnuts, have big, showy flowers, but the flower of oaks and ashes are so tiny you would hardly notice them. Trees pollinated by animals tend to have large flowers to attract the animals. Most trees pollinated by the wind have much smaller flowers. Many wind-pollinated trees have long clusters of flowers called catkins.