Acer negundo 'SENSATION' ash-leaved maple, box elder

Acer

The genus Acer belongs among woody plants that appeared very early in the Northern Hemisphere, and whose basic form has changed remarkably little since then, unlike many other tree groups. Tertiary fossils from Europe, Asia and North America already show leaves and fruits that would be instantly recognisable today, including the characteristic paired samaras. In Czechia, one of the best known fossil sites is Bílina, where petrified maple leaves and fruits from the late Tertiary period testify that these trees were part of the local landscape long before the arrival of humans. Scientifically, the genus was described by Carl Linnaeus (1707–1778) in his seminal work Species Plantarum in 1753, although its internal classification has been repeatedly revised since then. Today, botanists regard East Asia, particularly China, Japan and the Himalayan region, as the true centre of species diversity within the genus. Maples occupy an exceptionally wide range of habitats, from subtropical mountain forests to the cold regions of the temperate zone. They are among the trees that have accompanied human landscapes and cultures for a very long time.

Acer negundo, ash-leaved maple or boxelder, originates from North America, where it formed part of the everyday life of Indigenous peoples as well as later European settlers for centuries. It naturally grows along rivers, in floodplains and in open woodlands, where it functions as a fast growing and highly adaptable tree. At times when sugar maple was not readily available, sugar was commonly produced from its sap, albeit with lower yields and a milder flavour. The species was introduced to Europe in 1688, when it was cultivated in the gardens at Fulham near London by Henry Compton (1632–1713), one of the most important introducers of North American woody plants of his time. From there, boxelder gradually spread into botanical gardens and parks throughout Europe. In what is now the Czech Republic, it has been documented since 1835, when it appeared in the Royal Game Reserve in Prague’s Stromovka, from where it quickly spread into castle parks, urban greenery and the open landscape. Often this spread was not intentional. Based on long term scientific studies, boxelder has been shown to possess a high degree of invasiveness, which has led to the botanical species being excluded from recommended plantings and actively removed in many locations. In horticultural practice, therefore, only selected, predominantly sterile cultivars are used, as they do not pose a comparable risk to surrounding vegetation.