The Ailanthus of Mont des Arts

Most cities that have a Tree of Heaven at all have one nobody planted, since Ailanthus altissima spreads through cracked pavement and vacant lots so readily that it is treated as a weed across much of Europe and North America. This one is different: girthed at 321 centimetres, one of the widest trunks on this whole list, and formally inscribed on the region's legal register of remarkable trees, a species usually pulled out on sight given a rare pass because of its size and standing. It grows near the Mont des Arts, the raised garden terrace between Brussels' upper and lower town, built over an underground car park in the 1950s on a site that has carried some form of ornamental greenery since the 1910 World's Fair. Ailanthus was imported to Europe from China in the 18th century as an ornamental curiosity and a potential silk-moth host before anyone anticipated how aggressively it would naturalise; a specimen this large and this old getting protected status rather than removed is the exception rather than the rule. It stands free, in the open, a short walk from the garden's oak and its Caucasian wingnut.