The maple tree: the symbol of autumn colours

For centuries, trees of the Acer genus have fascinated different peoples and cultures with their elegance, their versatility of use and the vivid colours of their leaves, which in autumn tint nature with shades from bright yellow to deep red, crimson and scarlet. Maples, originating in Asia, Europe and North America, are renowned worldwide for their beauty, fine wood and production of the famous maple syrup. The name of this genus of plants, from the Latin Acer, meaning 'rugged' or 'sharp', reflects another of their distinguishing characteristics: the shape of their leaves, which in some cases almost resembles an open hand, is in fact characterised by a palmate structure, with lobes with pointed ends.

Maple belongs to a genus of deciduous plants in the Sapindaceae family, and includes over 128 species native to areas such as North America, Korea, Japan and Europe. These species, each with their own distinctive characteristics, thrive mainly in the temperate regions of the northern hemisphere, with the exception of Acer laurinum found in the southern hemisphere. The most widespread species in Europe and its mountainous areas is the Acer pseudoplatanus, or mountain maple, a large tree that can reach 25-40 metres in height and a trunk diameter of 3.5 metres. In Italy, the most widespread maple species are the aforementioned mountain maple, the curly maple (Acer platanoides) and the field maple (Acer campestre). In addition to these are non-native species often used as ornamental plants, such as the Acer negundo, native to North America or the Acer palmatum, from the Far East.

The symbol of the Canadian flag, the Acer saccharum, is the most common species of maple in North America, the centre of the production of the prized maple syrup. Although there are many maple species, in fact, only three are suitable for the production of this sweetener: the sugar maple (Acer saccharum), the black maple (Acer nigrum) and the red maple (Acer rubrum). The maple syrup production process is also delicate and intertwined with the climatic conditions in which maples live: during the summer and autumn seasons, the sun and rain allow these trees to accumulate water and sugar through photosynthesis, substances needed to cope with the harsh winter temperatures. Only once spring arrives is it then possible to collect the sap, which is consequently boiled down to a very concentrated solution, filtered and from which the famous syrup is obtained.

Maples are easily distinguished by their particular leaf structure: ranging in colour from green to yellow and red, and varying according to the season, maple leaves are generally webbed and divided into three, five or more lobes. While recognising a species of the Acer genus is fairly simple, recognising individual maple species is more complex. For example, the curly maple (Acer platanoides) and the sycamore maple (Acer pseudoplatanus) both have large leaves with five platy lobes, but can be distinguished by the presence (for the curly maple) or absence (for the sycamore maple) of cusped lobes. Again, the field maple (Acer campestre) has a leaf still with five lobes, but smaller and with rounded contours. Finally, the aforementioned Acer saccharum also has pentalobed leaves, but more lanceolate and with deep veins.

Another distinctive feature of the maple tree lies in the particular shape of its fruits: the samare. These fruits are composed of two 'winged' seeds contained in capsule-like structures, each of which has a membranous wing. The main characteristic of the samare is their ability to exploit the wind to disperse the seeds away from the mother tree, thanks to the rotary motion that the wings impart as they fall. This interesting and unique dispersal mechanism increases the probability of germination and growth of new plants in different areas far away from the mother tree.

Due to its beauty, elegance and special colours, the maple tree is at the centre of many European and non-European legends and symbolism. According to Greek mythology, for example, the maple tree was the tree of the god of fear, Phobos, and associated with it probably because of its deep red colour, reminiscent of blood. In Celtic tradition, on the contrary, the maple tree was believed to have magical properties and could protect houses from evil spirits. In North America, on the other hand, American Indians considered the maple a sacred tree and used its wood and sap for various ritual and everyday purposes.

Moving to the Far East, the maple tree has a unique symbolic importance in Japan. In the Japanese tradition, this tree, known by the term momiji(紅葉) has the same kanji as koyo(紅葉), indicating the autumn period when the colours of the leaves change, thus symbolising the splendour of autumn. During this season, in fact, the Japanese celebrate the Momijigari, literally "maple hunting" or "autumn colour hunting", a tradition that celebrates observing and admiring the incredible colouring of autumn foliage, which covers the Japanese landscape in yellow, orange and red hues. Momijigari originates from a custom of the aristocrats of the Heian period (794-1185), who would gather to read, play music and compose poetry under maple trees, admiring their colours. Today, this tradition has become popular throughout Japan to such an extent that predictions of leaf colour trends and developments are broadcast on TV.

Discover and recognise new species of maples (and more) with Biodiversa, the free game app for biodiversity monitoring and ecosystem protection that allows you to "collect" and easily identify the plants and flowers you come across during an outdoor walk. This ambitious citizen science project promoted by 3Bee aims to create a co-operative archive dedicated to flora (and in a second phase fauna) in Europe, involving player users with challenges to catalogue species, some of which are rare or endangered. Available for iOS and Android, Biodiversa has a dynamic similar to that of some well-known free-to-play video games that encourage moving and travelling in the real world to 'collect' characters. The app offers a gaming experience in which plants are all to be 'collected' and identified in order to collect experience points, level up and climb the leaderboard.