In Praise of Epimediums by RICHARD E. WEAVER, JR. The genus Epimedium consists of approximately twenty-five species of herbaceous perennials distributed primarily in China and Japan, but with a few in Europe, Asia Minor and North Africa. It is a member of the Barberry family, and its closest relative is Vancouveria, with three species on the West Coast of the United States. Their decorative foliage and odd but beautiful, softly colored flowers in the spring make the various species exceptionally fine plants for use as ground covers and as accent plants in the shady garden. The common name "Barrenwort," because decoctions of the roots of a plant confused with E. alpinum supposedly prevented conception in women, is seldom used in this country. I do not particularly care for it anyway, so I will call these plants by their Latin name. Relatively few species are widely cultivated in the United States, and the nomenclature of these is badly confused, making it difficult to know what one will receive when ordering from most nurseries. One purpose of this article is to clarify the nomenclature and to provide a means for identifying the various species, hybrids and clones in cultivation. The nomenclature used, with a few exceptions, is based on Dr. William Stearn’s monograph of the genus ( Journal of the Linnaean Society, Botany, Volume 51, pages 409-534, 1938); the observations are based on herbarium specimens and living plants in my garden. After the introductory material on culture and identi- fication, the species that have been cultivated in this country are treated first, followed by a section on their hybrids. In each section, closely related species are grouped together for purposes of com- parison. Epimediums are adaptable plants in the garden, flourishing and flowering well in shade or sun. A good soil, rich in humus, is desir- able. Their use in the garden depends on the species. Although often described as being good ground covers, only those few species that spread by elongate rhizomes are suitable for this purpose. The others do not spread sufficiently rapidly and are best grown as isolated clumps. Propagation is easily effected by division at most any time the ground is not frozen. I prefer to divide my plants before they flower in the spring or else in early summer after the foliage has fully matured. The resulting plants establish and flower more quickly than if they had been divided in the fall. 51 52 Dr. Steam noted the scarcity of mature fruits on the cultivated specimens and attributed this to the possibility that the plants are basically self-sterile and that most species and hybrids are represented in cultivation by single clones. In self-sterile plants, two clones are necessary for pollination to be effective and for seeds to be formed. In my garden, where many species and hybrids grow in close prox- imity, seed set is generally good. I have experimented with seed germination without success so far, and I suspect that the seeds must be collected as soon as ripe and immediately given a cold stratification. To assist in identification, I have prepared a key to the various species and their hybrids. But first, the characters used in the key need some explanation. The flowers are of rather curious construc- tion, and the parts must be understood for positive identification of many species. All flower parts are in series of four. Starting at their attachment to the pedicel or flower stalk (the apparently uppermost parts since the flowers nod or droop) the outer sepals are small and inconspicuous- and often fall off soon after the flowers open. The next ring, the inner sepals, are the most conspicuous parts of the flowers of most species. They would pass as petals to the casual observer, and they vary in color from pure white to reddish, purple, coppery and yellow. Next come the petals, and these vary greatly from species to species. In a few they are flat and resemble the inner sepals, but in most species they are modified into nectar-producing spurs or "horns," and these may be small and inconspicuous or they may be very showy, projecting far beyond the tips of the sepals. The entire petal may be spur-like, or the inner portion may be flattened, the bases of all four then forming a cup around the stamens. Figure 1 illustrates several representative flowers with the parts labeled. The foliage of most species, at least in a climate like that of New England, is deciduous or semi-evergreen. In the latter case the leaves persist through the winter, but by spring they are brown and battered. A few species have truly evergreen foliage. The leaves are always compound. In some species, they are divided into three leaflets, a condition termed ternate. In others, each segment is again divided into three, resulting in a biternate condition. The leaves are mostly basal, arising directly from the crown of the plant. A well defined group of species bears in addition a single leaf on the flowering stem. Several hybrids are variable in that they sometimes have a leaf on the flowering stem, while other flowering stems, or scapes, on the same plant are naked. The leaflets are basically heart-shaped or somewhat triangular in outline, but the side pair in each group of three is lopsided or un- equal at the base. They usually bear slender, often spiny-tipped teeth along their margins. Figure 2 illustrates the characters of the leaves. All species spread by underground rhizomes. In most species the rhizomes are short and the plants are then densely clump-forming. I 53 Figure 1. Flowers of Epi- medium with the parts labeled. A, E. diphyllum, adapted from Curtis’s Botamcal Magazine, vol. 62, plate 3448, 1835; B, E. X rubrum, bach view; C, E. X rubrum, front view, adapted from Curtis’s Botanical Maga- zine, vol. 93, plate 5671, 1867; D, E. pinnatum, adapted from Curtis’s Botanical Magazine, vol. 75, plate 4456, 1849; E, E. grandiflorum, adapted from Morrison & Decai- sne, Annales des Sciences Naturelles, Paris, vol. 2, plate 13, 1834. Figure 2. Characters of the leaves of Epimedium. A, a ternate leaf, show- ing the three leaflets with spiny-toothed margins; B, a biternate leaf; C, the leaf of E. diphyllum showing the characteris- tic two leaflets without teeth on their margins; D, a plant with basal leaves as well as a single leaf on the flowering stem; E, a plant with only basal leaves and a naked (leafless) flower- ing stem. Both figures prepared by Sheila Geary. 54 A few have elongated rhizomes, and these spread to form a mat. The latter group are the most satisfactory ones for use as ground covers. KEY TO THE CULTIVATED SPECIES AND HYBRIDS OF EPIMEDIUM 1. Spurs of petals absent, or present in some flowers and not others; leaves with only two leaflets. E. 2. Petals always spurless diphylluna , 2. Petals with spurs present in some flowers E. X youngianum 1. Spurs always present; leaves with three or more leaflets. 3. Spurs of the petals nearly as long as, to much longer than, the sepals; bases of the petals forming a cup-like structure around the stamens. 4. Flowering stem usually leafless; plants spreading by long rhi- zomes and forming mats E. X versicolor 4. Flowering stem with at least one leaf; plants densely clump- forming. 5. Spurs of the petals reaching to the tips of the inner sepals. 6. Inner sepals red; leaflets with numerous spiny teeth on margins E. X rubrum - 6. Inner sepals white; leaflets with a few scattered teeth on margins E. X youngianum 5. Spurs of the petals projecting conspicuously beyond the . -.- tips of the inner sepals. 7. Flowers creamy yellow E. koreanum 7. Flowers white to rose-colored or purple. 8. Flowers pure white; leaves evergreen E. sempervirens 8. Flowers colored, the spurs sometimes white but the inner sepals always at least tinged with rose or purple; leaves deciduous E. grandiflorum 3. Spurs of the petals inconspicuous (at least much shorter than the inner sepals) or absent; bases of the petals not forming a cup-like " structure around the stamens. 9. Flowering stem leafless. 10. Inner sepals coppery-orange in color E. X warleyense 10. Inner sepals bright yellow. 11. Leaves with 3 leaflets with distinctly spiny margins; spur of petal projecting away from sepal .. E. perralderianum 11. Leaves with 5-9 leaflets (rarely 3); leaflets nearly spineless or with inconspicuous, scarcely projecting spines; spur of petal lying flat against sepal E. pinnatum 9. Flowering stem with at least one leaf. 12. Inner sepals coppery-orange in color E. X warleyense 12. Inner sepals red, purple, pink or white. 13. Sepals and petals similar in appearance and equally conspicuous, the petals sometimes spurless; mature leaflets less than an inch broad E. X youngianum 13. Sepals and petals very different in appearance, the sepals by far the more conspicuous, the petals al- ways reduced to small spurs; mature leaflets more than an inch broad. Epimedium diphyllum. Photo: R. Weaver. I 55 14. Basal leaves with 3 leaflets; flowers tiny, scarce- ly 1/4 inch across E. sagittatum 14. Basal leaves with more than 3 leaflets, flowers _ larger. 15. Plants tightly clump-forming; leaves near- ly evergreen; inner sepals pale rose or nearly white E. pubigerum 15. Plants spreading by long rhizomes, form- ing mats, leaves deciduous; inner sepals dark red . E. alpinu~n Epimedium diphyllum A low, dainty and slow-spreading species, this would never do as a ground cover. Rather, it requires careful placement in the garden to avoid being lost.