Maple

The genus *Acer* contains a diverse group of approximately 132 species of trees and shrubs known as maples. These plants belong to the soapberry family, Sapindaceae, and are found across much of the Northern Hemisphere. Most species are native to East Asia, but they also appear in Europe, North America, and northern Africa. Only one species, *Acer laurinum*, grows in the Southern Hemisphere. Maples are highly valued by humans for many reasons. Some provide sap for making maple syrup, while others are prized in horticulture for their autumn colors and decorative foliage.

Most maples exhibit a specific growth pattern called opposite leaf arrangement. This means that leaves grow in pairs directly across from one another on the stem. The leaves are typically palmate, meaning they are shaped like a hand with lobes. These lobes are defined by three to nine veins that lead from the base to the tip. However, there are exceptions to this rule. For example, the box-elder (*Acer negundo*) has pinnately compound leaves with five to nine leaflets. Some species, like the paperbark maple (*Acer griseum*), have trifoliate leaves, which means they grow in groups of three.

One of the most distinctive features of the maple is its fruit, known as a samara. These are often called "maple keys" or "helicopters" because of how they move. Each samara consists of a seed enclosed in a nutlet attached to a thin, papery wing. When the fruit falls from the tree, the wing causes the seed to spin rapidly. This spinning motion allows the wind to carry the seed a considerable distance from the parent tree. This mechanism is so efficient that during World War II, the US Army designed an airdrop supply carrier based on the shape of a maple seed.

The evolutionary history of maples is quite ancient. The oldest known *Acer* fossils date back to the late Paleocene, roughly 60 million years ago. These early fossils have been found in Northeast Asia and northern North America. In Europe, the oldest fossils were discovered in Svalbard and date to the late Eocene. Molecular studies using DNA from chloroplast and nuclear genomes suggest the group originated in the northeastern Palearctic. After appearing, the maples underwent rapid lineage divergence and dispersed into the Nearctic and Western Palearctic regions.

Maples vary greatly in their physical structure and habitat. Most species are trees that grow to significant heights, though some are shrubs less than 10 meters tall. Many maples are deciduous, meaning they lose their leaves annually. This process often results in the famous autumn colors that gardeners love. A few species in the Mediterranean and southern Asia are evergreen, keeping their leaves year-round. Many maples are shade-tolerant when they are young. They often grow as understory or riparian species, though the sugar maple can sometimes form monodominant forests.

In the world of gardening, maples are incredibly popular. The Japanese maple (*Acer palmatum*) is a standout example, with over 1,000 different cultivars. These cultivars are often created through asexual reproduction, such as grafting or budding. Some maples are even used in the art of bonsai, where they are grown in small pots to look like miniature trees. People also plant them for their unique bark or flowers. For instance, the *Acer griseum* is frequently grown specifically for its decorative bark.

Beyond science and gardening, maples hold great cultural significance. The maple leaf is a powerful symbol of strength and endurance. It is most famously used on the national flag of Canada. The design on the Canadian flag is a stylized eleven-point leaf modeled after the sugar maple. Maples are also part of the identity of many places, such as the coat of arms of Sammatti in Finland. Because they are so widespread and beautiful, maples have become an enduring part of human history and global symbolism.