Epimedium, also known as barrenwort, bishop's hat, fairy wings, horny goat weed, or yin yang huo (Chinese: 淫羊藿; pinyin: Yínyánghùo; Wade–Giles: Yin²-yang²-huo⁴), is a genus of flowering plants in the family Berberidaceae.

While there is little clinical evidence to date, as sildenafil, vardenafil, and tadalafil – sold under the brand names Viagra, Levitra and Cialis – are all based on (stronger) PDE5 inhibitory action, it is thought to have erectogenic properties and is found in some men's sexual health supplements.

[2] One of the common names for the genus, bishop's hat, arises from the shape of the flowers, particularly where the spurs are longer than the sepals.

[citation needed] The genus was given its name by Carl Linnaeus in 1753, in describing the European species E. alpinum.

The initial assumption that the plants would only thrive where their native conditions could be closely replicated have proven to be overly cautious, as most varieties are proving extraordinarily amenable to general garden and container cultivation.

[8] While they can be successfully propagated in early spring, epimediums are best divided in late summer, with the aim of promoting rapid re-growth of roots and shoots before the onset of winter.

Several breeders (in particular Darrell Diano Probst, Tim Branney & Robin White) have also undertaken their own hybridization programmes with the genus.

Various new nursery selections are gradually appearing in the horticulture trade, the best of which extend the colour and shape range of the flowers available to the gardener.