Popping up here and there in gardens around Capitol Hill are the flowers of a plant that seems to have come from a Seussian landscape. With beautiful evergreen blue-green leaves and now topped with large clusters of striking chartreuse disks, these spurges (Euphorbia) are popular shrubs for adding a bit of dramatic flair to yards and planters.
The most commonly planted species is the Mediterranean spurge (Euphorbia characias), native to southern Europe, but several other species in the genus, including wood spurge (Euphorbia amygdaloides) are occasionally seen.
So what exactly are those chartreuse disks? Flowers would be the obvious answer, but take a closer look and they don’t appear quite like what one would expect.
A typical flower has petals, stamens (the male parts producing pollen), and a pistil (the female part producing seeds) inside. The spurge has something that looks similar, but each disk actually holds a collection of multiple flowers. The disk is a bract, or modified leaf, and above the bract are very small flowers and oftentimes a pair of additional bracts, each with its own cluster of tiny flowers. Each flower is highly reduced and consists of just a single small yellow stamen or a single green 3-lobed pistil. The unisexual flowers are surrounded by brown or yellow glands which produce nectar. This very unique arrangement of flowers is called a cyathium and is found throughout the genus Euphorbia.
You have almost certainly seen a cyathium before. The genus Euphorbia is among the largest in the plant kingdom with about 2000 species, and one of those is that favorite Christmas plant, the poinsettia (Euphorbia pulcherrima), which has cyathia above bright red bracts.
Another interesting feature of the spurge is found in the leaves and stems. When they are broken or damaged, they exude a milky-white and sticky sap that offers the plant protection against herbivores. The sap is toxic and irritating, and gardeners working with the plant should take care to avoid prolonged exposure on the skin. Milky sap, or latex, is common throughout the relatives of Euphorbia.
The latex of another species in the Euphorbia family, the rubber tree (Hevea brasiliensis), is tapped to make natural rubber.