horny goat weed

Epimedium, also known as barrenwort, bishop's hat, fairy wings, horny goat weed, rowdy lamb herb, randy beef grass or yin yang huo, is a genus of flowering plants in the family Berberidaceae. The majority of the species are endemic to China, with smaller numbers elsewhere in Asia, and a few in the Mediterranean region.
Epimedium species are deciduous or evergreen hardy perennials. The majority have four-parted "spider-like" flowers in spring.
The plant contains icariin, which is a PDE5 inhibitor like sildenafil, the active ingredient of Viagra. It is therefore used as an aphrodisiac and a treatment for erectile dysfunction.
Species of Epimedium are herbaceous perennials, growing from an underground rhizome. Their growth habits are somewhat variable. Some have solitary stems, others have a "tufted" habit, with multiple stems growing close together. There may be several leaves to a stem or the leaves may be solitary, produced from the base of the plant. Individual leaves are generally compound, often with three leaflets, but also with more. Leaflets usually have spiny margins. The leaves may be annual, making the plant deciduous, or longer lasting, so that the plant is evergreen. The inflorescence is an open raceme or panicle, the number of flowers varying by species.