2. Euonymus L.

(Ma, 2001)

Plants small trees or shrubs, sometimes trailing or climbing but not twining (anchored to the substrate by adventitious roots). Twigs 4-angled or sometimes circular in cross-section, sometimes with corky wings. Leaves opposite, deciduous or partially to completely evergreen, short-petiolate. Leaf blades variously ovate to elliptic or obovate, the margins entire or finely toothed, the surfaces glabrous or inconspicuously hairy. Inflorescences axillary clusters or small panicles or the flowers occasionally solitary in the leaf axils. Flowers usually perfect (rarely functionally staminate or pistillate). Sepals 4 or 5, fused toward the base. Petals 4 or 5. Stamens 4 or 5, these inserted along the margin of the nectar disk, the filaments minute (0.1–0.5 mm). Ovary usually with 1–5 locules and 2–6 ovules per locule. Style short, stout, the stigma entire or shallowly 3-lobed. Fruits ovoid or more or less globose, sometimes (2)3–5-lobed, pink to red, dehiscent by (2)3–5 valves. Seeds ovoid to ellipsoid, 1 or 2(–6) per locule, brown, each enclosed in a fleshy red to orange aril. About 130 species, nearly worldwide.

The taxonomy of Euonymus has been somewhat confused. There is considerable variation in growth habit and leaf characters, with many variants sometimes receiving separate names and numerous species described from horticultural selections of Asian origin. Many of these problems, especially those concerning the Oriental species, were addressed by Ma (2001), who reduced the number of accepted species from 200 or more to 129.

The generic name Euonymus has engendered a lot of controversy. Linnaeus (1753) spelled it “Evonymus” in his Species Plantarum and “Euonymus” in his Genera Plantarum (Linnaeus, 1737). After decades of debate (Zijlstra and Tolsma, 1991), the spelling Euonymus was conserved at the International Botanical Congress in Tokyo in 1993. Also, Linnaeus (1753) treated Euonymus and its species with a masculine (-us) ending, but the classical Greek root is considered feminine. After decades of inconsistent species-epithet endings, Paclt (1998b) made a formal proposal to conserve the name as feminine (with -a rather than -us) for the species epithets. However, the Committee for Spermatophyta of the International Association of Plant Taxonomy, which must approve such proposals before they can be voted upon at an International Botanical Congress, chose not to favor Paclt’s view (Brummitt, 2000). The generic name (and thus specific epithets) therefore must be treated as masculine.

Polyembryony has been reported in E. americanus and E. alatus (Brizicky, 1964a). The seeds of these species contain up to nine embryos, many of them small and apomictic. Only two chromosome levels, 2n=32 and 2n=64, have been reported for Euonymus, the latter possibly arising following past interspecific hybridization (Nath and Clay, 1972). Several species of Euonymus are prized for their colorful fall foliage and attractive fruits with bright red arillate seeds. Although sometimes used in folk medicine, the bark and fruits generally are considered poisonous.