About 60 species in cultivation, including:
Epimedium, also known as Rowdy Lamb Herb, Barrenwort, Bishop's Hat, Fairy Wings, Horny Goat Weed, or Yin Yang Huo (Chinese: 淫羊藿), is a genus of about 60 or more species of herbaceous flowering plants in the family Berberidaceae. The large majority are endemic to southern China, with further outposts in Europe, and central, southern and eastern Asia.
Some varieties and hybrids have been in Western cultivation for the last 100 to 150 years. There are now a wide array of new Chinese species being cultivated in the west, many of which have only recently been discovered, and a number of which have yet to be named. There are also many older Japanese hybrids and forms, extending the boundaries of the genus in cultivation. The majority of the Chinese species have not been fully tested for hardiness or indeed for any other aspect of their culture. 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.
While they can be successfully propagated in early spring, Epimedium are best divided in late August, with the aim of promoting rapid re-growth of roots and shoots before the onset of winter. Several breeders (in particular Darrell Probst, Tim Branney & Robin White) have also undertaken their own hybridization programmes with the genus Epimedium. Various new nursery selections are gradually appearing in the nursery trade, the best of which are extending the colour and shape range of the flowers available to the gardener.
Hugely popular as garden plants for centuries in Japan, Epimedium are only just beginning to garner attention in the West. While they vary somewhat in their respective hardiness, all are essentially dwellers of the forest floor, and, as such, all require fundamentally similar conditions of moist, free draining, humus rich soil and cool shade, with some shelter for the newly emerging leaves. Some of the more robust varieties are often recommended as plants for dry shade, and whilst their tough foliage and stout rhizomes can allow them to grow successfully in such conditions, (and in more open, exposed positions too, in some instances) they will certainly not give their best. Furthermore, dryness and exposure will pretty much guarantee the early death of many of the newer and more delicate species.
Given suitable conditions most Epimedium will form beautiful ground cover plants, often with magnificent new leaves tinted in bronze, copper and reds combining with a huge variety of flower colours and forms in spring. Handsome and dense-growing foliage remains present for much of the year, with the leaves often turning purple, crimson and scarlet in autumn in some forms, and remaining evergreen in others. With all varieties, however, the foliage is best cut off at ground level shortly before new leaves emerge, so as to fully reveal their beauty of form and colour. Ideally, a mulch should then be applied to protect the new growth from frosts.
From the gardeners point of view Epimedium flowers comprise two main parts, the inner sepals, which are petal-like and four in number (the four outer sepals are small, insignificant, and rapidly shed as the flowers open) and the petals, which are held within the sepals. In some species these petals have developed long spurs and in such plants they greatly exceed the size of the surrounding sepals, producing a flower shaped like an inverted crown, and also giving rise to the one of the common names for Epimedium- bishops hat. In other species, however, (such as E. perraldianum) the petals are reduced to tiny spurs, and it is the greatly enlarged and highly coloured sepals that have expanded to catch the attention of the wandering insect.
Many species of Epimedium are alleged to have aphrodisiac qualities. According to legend, this property was discovered by a Chinese goat herder who noticed sexual activity in his flock after they ate the weed. It is sold as a health supplement; usually in raw herb, tablet, or capsule form and sometimes blended with other supplements. The over-exploitation of wild populations of Epimedium for use in traditional Chinese medicine is having potentially serious consequences for the long-term survival of several species, none of which are widely cultivated for medicinal purposes.
Icariin is purported to work by increasing levels of nitric oxide, which relax smooth muscle. It has been demonstrated to relax rabbit penile tissue by nitric oxide and PDE-5 activity. Other research has demonstrated that injections of Epimedium extract directly into the penis of the rat results in an increase in penile blood pressure.
Like sildenafil (Viagra), icariin, the active compound in Epimedium, inhibits the activity of PDE-5. In vitro assays have demonstrated that icariin inhibits PDE-5 with an IC50 of around 1 micromolar, while sildenafil has an IC50 of about 6.6 nanomolar (.0066 micromolar) and vardenafil (Levitra) has an IC50 of about 0.7 nanomolar (.0007 micromolar). Measured differently, the EC50 of icariin is approximately 4.62 micromolar, while sildenafil's is .42 micromolar. The amount of oral administration of Epidemium extract necessary to achieve these relative concentrations is unclear from the literature.
A recently published Italian study modified icariin structurally and investigated a number of derivatives. Inhibitory concentrations for PDE-5 close to sildenafil could be reached. Moreover, the most potent PDE-5 inhibitor of this series was also found to be a less potent inhibitor of phosphodiesterase-6 (PDE-6) and cyclic adenosine monophosphate-phosphodiesterase (cAMP-PDE), thus showing it to have more specificity for PDE-5 than sildenafil.
Epimedium has been shown to up-regulate genes associated with nitric oxide production and changes in adenosine/guanine monophosphate balance in ways that other PDE5 inhibitors do not.
Classification System: APG II (down to family level)
Ordo: Unassigned Eudicots
Species: E. acuminatum - E. alpinum - E. brevicornu - E. davidii - E. diphyllum - E. dolichostemon - E. fangii - E. fargesii - E. franchetii - E. grandiflorum - E. koreanum - E. latisepalum - E. macranthum - E. membranaceum - E. mikinorii - E. perralderianum - E. pinnatum - E. pubescens - E. pubigerum - E. sagittatum - E. sempervirens - E. stellulatum - E. wushanense