Perforate St. John's Wort is a perennial herbaceous plant. It has a branched stem with two ribs and can grow to a height of 30 to 60 centimetres. It has opposing, stalkless, narrow leaves that appear to have many tiny holes through them, although these are actually colourless glands. The star-shaped flowers are bright yellow, peppered with tiny black dots. The fruit is a three-winged capsule containing multiple seeds. The stems exude a blood-red juice.
St. John's wort blooms from June to August, and its fruit ripens in September. It grows in meadows, woodland and waste ground and can be found in many countries throughout the world.