Marin IJ Articles

Euphoric over Euphorbias

Euphorbia is the largest genus of plants with over 2000 species existing worldwide. They have evolved into a myriad of forms from tiny annuals to trees. The best known of all euphorbias is probably poinsettia (Euphorbia pulcherrima) whose red leaves brighten up many homes at Christmas. On a trip to Tenerife in the Canary Islands, we found the canopy of one large specimen provided enough shade for our picnic.

The 2000 species of Euphorbia share a collection of characteristics found in no other group of plants. The flowers have no sepals or petals and are borne at the top of the plant at the end of the current year’s growth. What is called the “flower” is in fact technically a cyathium, consisting of fused bracts that form a cup around the much-reduced true flowers. The stem leaves are never lobed or divided and the edges of the leaves are either smooth or slightly serrated.

A great number are succulent plants with sharp thorns and no leaves except after rains. The easiest way to determine whether a plant is a euphorbia or a cactus is to lightly scratch the stem and if the liquid emerging is clear then the plant is a cacti, if it is a white sticky sap then the plant is a euphorbia.

The presence of sap does not prove that a plant is a euphorbia, but the absence of sap does prove that a plant is not a euphorbia. Ideally, you should not allow the sap to come into contact with your skin as some people react with a nasty rash or blistering that can last for a few days. Gloves and long sleeved clothing are normally adequate protection. Fortunately, most gardeners find the most irritating effect of the sap is to gum up the blades of shears when pruning. The sap has been used in many different ways, ranging from an anti-tumor drug in China where it has been in use for 2,000 years to a treatment for bee and scorpion stings in Uganda.

The choice of which herbaceous euphorbia to use in your garden depends on the size of your border. I like the sharp combination of the Euphorbia characias wulfenii against a backdrop of dark purple flowers or bronze foliage. Another interesting and eye-catching combination would be Euphorbia ´ martinii with blue geraniums and rosemary. Many have tried to describe the nebulous nature of the color of euphorbias but there is no universally accepted word to describe it. Green, acid green, lime-green and chartreuse have all been used.

With such a large group, there are several species that have become a nuisance, even invasive in some parts of the country. Euphorbia esula (leafy spurge) is one such plant and can be found at scattered locations in northern California. Populations have been found in Sonoma County and as far south as Los Angeles County. The larvae of several species of beetles (they feed on the roots) have been successful in controlling some infestations that herbicides failed to kill. Fortunately, leafy spurge infestations here are currently small. The California Exotic Pest Plant Council lists caper spurge (Euphorbia lathyris) as a possible threat to wildlands.