Here's a word to add to your garden vocabulary: Euphorbia. This is not to be confused with euphoria. How did a plant family get such a curious botanical name?   

The family is named for Euphorbos, a Greek physician who lived more than two thousand years ago. He wrote about a succulent plant, similar to Euphorbia, that he believed was a potent laxative.  

All Euphorbia have one thing in common: a white milky sap that is caustic, an irritant to humans, dogs, and cats. The causticity varies among species. In Roman times, the sap was used to treat a variety of illnesses. It is caustic enough to keep deer and cattle from grazing on plants in this family.  

The Euphorbia family contains more than 2,000 different plants, including perennials, annuals, biannuals, and many succulents. The common name for some of them is spurge. Poinsettia (Euphorbia pulcherrima) is a member of the family. I once saw a hedge of poinsettia in Southern California blooming in summer. The flowers were much smaller than the potted poinsettia we see in nurseries at Christmas. 

Euphorbia flowers are unusual in being either male or female. They don't have all the parts they need for reproduction and rely on bees, other insects, and bats to help them create seed. In contrast, tomato blossoms have both male and female parts and will self-pollinate with help from wind, bees, or deliberate agitation.  As I walk by my blooming tomatoes, I give them a good shake.

Milkweed (Asclepias species), the host plant for monarch caterpillars, also produces white sap but is not a Euphorbia. Even so, its sap can be painful. 

Castor bean (Ricinus communis) is a member of the Euphorbia family. Originally from Africa, the plant is now cultivated in many places for its oil, which is used in a variety of products. The seed pod contains sap, but the seed, the source of the oil, does not.  

The castor bean plant is thought to deter moles. These small creatures tunnel through the soil looking for worms and other food. Their tunnels divert water from plants and can wreak havoc in the landscape, so an effective deterrent would be welcome. My war with moles has been going on for some time and so far, they are winning.  

You may be surprised to know that you are driving around on a member of the Euphorbia family.   The rubber tree (Hevea brasiliensis) is a Euphorbia. Automobile tires are made from natural latex, the tree's milky sap. This plant originates in South America but is now grown in many tropical countries. Workers cut the bark and collect the latex, which is used in the manufacture of everything from rubber tires to rubber gloves.  

Some Euphorbia are weeds but many are desirable landscape plants. Most are drought tolerant. During my research, I discovered Euphorbia marginata ‘Early Snow,' which has variegated leaves and interesting white flowers. I intend to plant it and deepen my connection to this amazing family.  

Workshop: Join the UC Master Gardeners of Napa County for a hands-on workshop on “Garden Pest Management” on Saturday, April 30, from 11 a.m. to 1 p.m., at Las Flores Community Center, 4300 Linda Vista Avenue, Napa. Bring gloves and wear gardening attire. Event will be canceled in the event of rain. Registration required or register at 

https://bit.ly/3v8a7Y7.

Library Talk: Join Napa County Master Gardeners and the Napa Library for a free talk on “Soil is the Solution: Healing the Earth One Yard at a Time” on Thursday, May 5, from 7 pm to 8 pm, via Zoom. Register to receive the Zoom link at http://ucanr.edu/2022MaySoilSolutionLibaryTalk.

Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to mastergardeners@countyofnapa.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email. For more information visit https://napamg.ucanr.edu  or find us on Facebook or Instagram, UC Master Gardeners of Napa County.