Hypericum hirsutum is a downy perennial plant that grows to two or three feet. It has erect stems and opposite pairs of untoothed, elongated oval leaves with translucent glandular dots. The terminal inflorescences have many pale yellow flowers. Each has five pointed sepals with stalked black dots on the margins. The five petals also may have black dots and the many stamens are in bundles. Hairy St John's wort is very similar to common St John's wort (H. perforatum) but can be distinguished by the downy stems and the much longer leaves.
H. hirsutum grows in poor grassland on well-drained clay, limy and chalky soils. It is often found at the edges of woodland, on river banks and roadside verges. It is found throughout Western Europe, and in the United Kingdom it flowers from July to August.
- "BSBI List 2007". Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-01-25. Retrieved 2014-10-17.
- McKlintock, D. and R. S. R. Fitter. The Pocket Guide to Wild Flowers. (1956) Collins, London. P29.
- Hypericum hirsutum Flora Europaea. Retrieved 2011-09-13.
- Hypericum hirsutum Emorsgate Seeds. Retrieved 2011-09-13.
- Miquelianin and other polyphenols from Hypericum hirsutum. G. M. Kitanov, Chemistry of Natural Compounds, Volume 24, Number 1, pages 119-120, doi:10.1007/BF00597593