Himalayan balsam is the tallest annual in Europe, commonly attaining a height of 2m and can even reach 3m at maturity in deciduous woodland. Himalayan balsam is an attractive plant with erect, hollow green stems with a reddish tinge. Branching occurs up the stem and the branches are arranged in whorls of 3. Leaves are lance shaped, always longer than they are wide and have serrate margins. Flowers are variable in colour from purple to pink and occasionally almost white and are produced from June through to October, long after most native annual plant species have matured. Seeds are large and black in colour at maturity, and produced in capsules, which open explosively when ripe; hence, the other common names for this plant are ‘Touch-me-not’ and ‘Jumping Jack’.