Himalayan balsam Impatiens glandulifera was introduced to Britain's gardens in the early 19th century. This pretty invader is now a widespread problem throughout Scotland. A native to the West and Central Himalayas it has escaped its natural predators and thrives largely unharmed in Scotland. After flowering the ripe seed pods explode, scattering seed up to 5 metres from the parent plant. The seeds are also easily transported along watercourses.