Acer, commonly known as maples, is a genus of approximately 132 species of deciduous and evergreen trees and shrubs in the family Sapindaceae. Trees in this genus typically grow between 10 and 45 metres tall, though some species take a multi-stemmed shrub form. All maples share two defining traits: leaves arranged in opposite pairs and distinctive winged fruits called samaras, often produced in pairs that spin like helicopter blades when they fall. Flowers are small, regular, and pentamerous, appearing in late winter or early spring before or alongside the emerging leaves.
The vast majority of maple species are native to East Asia, with additional diversity across Europe, northern Africa, and North America. Only a single species, Acer laurinum, reaches the Southern Hemisphere. Many maples are shade-tolerant in youth and commonly occupy riparian corridors or pioneer disturbed habitats. Root systems tend to be dense and fibrous, and several species spread clonally via root sprouts.
Maples have been cultivated for centuries for their spectacular autumn foliage, fast growth, and timber. Japanese maple (Acer palmatum) alone encompasses over 1,000 named cultivars. Sugar maple sap is the source of maple syrup — roughly 40 litres of sap yield one litre of finished syrup. The genus also provides tonewood for stringed instruments, hardwood for sports equipment, and pulpwood for paper production. The maple leaf is the national symbol of Canada, appearing on the country's flag and coat of arms.
Fossil evidence places the genus in the late Paleocene of Northeast Asia and northern North America, approximately 60 million years ago, making Acer one of the better-documented tree genera in the plant fossil record.
Etymology
The common name "maple" is first attested in English in 1260 as "mapole." The Latin genus name Acer is ancient and was used by Roman writers; it is thought to derive from a word meaning "sharp" or "hard," possibly referencing the wood's hardness, though the precise etymology remains debated.
Distribution
Maples are most diverse in East Asia, particularly China, Japan, and the Himalayan region. Additional species occur across Europe, the Caucasus, northern Africa, and North America. Only Acer laurinum extends to the Southern Hemisphere. In Europe, nine species are documented in Switzerland alone, including field maple (A. campestre), Norway maple (A. platanoides), and sycamore maple (A. pseudoplatanus). The genus is generally absent from tropical lowlands; in Asia, many species inhabit open ravines on shady slopes at elevations of 2,400–3,300 metres.
Taxonomy
Acer was formally described by Carl Linnaeus in Species Plantarum (1753, page 1054) and is placed in the family Sapindaceae, subfamily Hippocastanoideae. The type species is Acer pseudoplatanus (sycamore maple). Molecular phylogenetics show the genus's closest living relative to be Dipteronia, a small genus endemic to China, followed by Aesculus (horse chestnuts). GBIF recognises 589 descendant taxa under the genus, including accepted species, synonyms, and fossil taxa. The fossil record of Acer extends to the late Paleocene (~60 million years ago) in Northeast Asia and northern North America, with European occurrences appearing in the Svalbard record from the late Eocene.
Ecology
Maples are characteristically shade-tolerant in early life stages and frequently colonise disturbed riparian habitats or forest margins. Root systems are dense and fibrous, and several species form clonal colonies via root sprouts. Acer species host distinct insect communities; aphid assemblages vary considerably between host species. Significant pest threats include caterpillars, the invasive Asian long-horned beetle (Anoplophora glabripennis), and various aphid species. Fungal diseases of note include Verticillium wilt, sooty bark disease, and tar spot caused by Rhytisma species. Many maple species exhibit allelopathic properties, inhibiting the growth of neighbouring plants through root or litter chemistry.
Cultivation
Maples are among the most widely planted ornamental trees in temperate horticulture, valued primarily for brilliant autumn foliage, shade, and adaptability. Japanese maple (Acer palmatum) is particularly popular, with more than 1,000 registered cultivars ranging from dwarf shrubs to small trees with dissected or coloured leaves. Norway maple, silver maple, and red maple are common street and park trees in North America and Europe. Maples are also among the most popular subjects for bonsai.
For best performance, maples prefer moist, well-drained soils in full sun to partial shade. They tolerate heavy clay but may develop iron chlorosis in strongly alkaline conditions. Most species inhibit nearby plant growth through allelopathic compounds in root exudates or decomposing leaf litter, a factor worth considering in mixed plantings.
Propagation
Maple seeds (samaras) have a dormancy requirement and germinate most reliably when sown fresh in autumn or after cold stratification at 1–8°C for 2–4 months. Vegetative propagation is feasible: layering of branches typically takes about 12 months to produce a rooted plant, while softwood or semi-hardwood cuttings taken from young shoots in summer root well with the application of rooting hormone.
Cultural Uses
Maples have deep cultural and economic significance across multiple continents. In North America, sugar maple (Acer saccharum) sap is the raw material for maple syrup and maple sugar — producing one litre of syrup requires approximately 40 litres of sap, and Quebec is among the world's largest commercial producers. The maple leaf is the national symbol of Canada, appearing prominently on the national flag and coat of arms, and maple is Canada's official national tree.
Maple wood is prized for hardwood applications: sugar maple is used in bowling alleys, pool cues, and butcher's blocks, and maple bats were introduced to Major League Baseball in 1998. The wood also serves as an important tonewood in instrument-making, used for violin backs, viola bodies, cello backs, and the necks of electric guitars, where its density and bright acoustic character are valued. With a lignin content of approximately 21%, maple is also commonly processed into high-yield pulp for paper production.
In Japan, the autumn display of maple foliage — especially that of Acer palmatum — is the subject of momijigari, a traditional practice of going into the mountains or parks to view autumn colours, a cultural counterpart to cherry-blossom viewing in spring.
Conservation
Fifty-four species of maples meet the IUCN Red List criteria for being under threat of extinction. The greatest concentration of threatened species is in East Asia, where habitat loss, deforestation, and over-collection for the ornamental trade put many endemic species at risk.
