Euphorbias are simply incredible.
Over my many years of visiting various botanical gardens, arboretums and nurseries, I’ve developed a great fondness for and sense of amazement about this genus of plants. Almost every time our family visits a new public garden, we encounter yet another Euphorbia species, and we exclaim in near disbelief, “That’s a Euphorbia too?!”
Euphorbias are an astonishingly variable and diverse group of plants, with forms that include succulents and spiny, cactuslike species; low-growing groundcovers; leafy, decorative shrubs, some with brilliantly colored, flower-like structures; tall, sculptural trees; and small, pesky, weedy species that I hope never to see in my garden again!
The genus name Euphorbia comes from the ancient Greek physician Euphorbus, who purportedly discovered the plants. The leafy, nonwoody forms of Euphorbia are often called “spurges,” a name that derives from the Old French word espurgier and the Latin word expurgare. Both of these words mean “to purge,” since the sap of some Euphorbias was historically used as a laxative or purgative medication.
There are more than 2,100 identified species in the genus Euphorbia. They’re native to locations around the world, occurring naturally on every continent except for Antarctica. Depending on the species, they can be annual (with a lifespan of one year), biennial (with a lifespan of two years), or perennial (living for many years). They can also be evergreen (holding their leaves throughout the year) or deciduous (dropping their leaves seasonally).
Despite their many differences, Euphorbias do have a few characteristics in common. One is their white, milky sap or latex. In some species this sap is only mildly toxic or irritating, but in other instances it’s poisonous, so it’s always wise to be cautious and wear gloves and eye protection when touching or pruning these plants.
Culturally, Euphorbias all require well-drained soil; many species naturally grow in poor, sandy, or rocky soils. Their water needs are generally low, and most types require plenty of sun exposure and a warm to hot, frost-free climate (although some species are cold hardy).
Plants in the Euphorbia genus also have unique flowering structures called cyathia. Each cyathium is composed of a cluster of tiny, true, male and female flowers surrounded by a cup of fused bracts (modified leaves). In some species, a whorl of larger, colorful, petal-like bracts appears below the cyathia.
The poinsettia (Euphorbia pulcherrima) — described in detail in last week’s article — is probably the best-known species in the Euphorbia genus. Another Euphorbia commonly seen in our area is spotted spurge (Euphorbia maculata), a tenacious, self-sowing, low-growing, readily spreading weed. You can learn more about this garden pest on the UC IPM website (http://ipm.ucanr.edu/PMG/PESTNOTES/pn7445.html).
Besides a table-top poinsettia, my personal Euphorbia collection includes these indoor and outdoor plants:
African Milk Tree (Euphorbia trigona). This was the plant that first introduced me to Euphorbias, since I inherited a potted specimen from my paternal grandmother many years ago. It has three-sided, rigid, succulent green stems adorned with short spines and small ovoid leaves, and it has slowly branched and grown upright to nearly six feet tall. I now also have a more colorful cultivar named “Rubra,” which has very pretty, red-tinged stems and leaves.
Ascot Rainbow Spurge (Euphorbia x martinii “Ascot Rainbow”). This small perennial shrub has narrow, variegated leaves of blue-green and creamy yellow that emerge in all directions from long, thin, fleshy stems. Its leaves develop a glowing blush of rosy pink in colder temperatures. These plants bloom in early summer to fall, with large sprays of bright yellow-green cyathia that grow from the top of each stem.
Euphorbia Inconstantia (E. inconstantia). This is a cactuslike species that grows in a compact clump of thick, columnar, succulent, bluish-green stems. Its upright growth reaches a height of one to two feet, and the stems are deeply ribbed, with an array of sturdy grey spines emerging along the outer edge of each rib.
A couple other noteworthy Euphorbia species are:
Pencil Cactus, Pencil Bush, or Milk Bush (Euphorbia tirucalli). This plant is spineless and isn’t a true cactus, but it does have toxic sap containing terpenes and other corrosive chemical compounds (giving it the name of “Petroleum Plant” in some countries). The species plant has bright green, thin, many-branched, vertical succulent stems that reach a height of 2 feet or more. The named cultivar ‘Sticks on Fire’ has stems that transition from bright green at the base to pink and vivid coral red at the ends. It’s a gorgeous accent plant, especially when paired with a succulent having blue-green leaves.
Crown of Thorns (Euphorbia milii). This native of Madagascar has one of the showiest flowering displays of any Euphorbia. Its woody grayish-brown stems are covered with long sharp spines, but each stem is topped with large, rich green leaves and a tight cluster of flower-like cyathia that resemble single begonias. Depending on the variety, the bracts can be pale to bright pink, intense red, creamy yellow, or variegated in color.
For more history, pictures, and descriptions of the different species of Euphorbias, consult these sources:
• The “Sunset Western Garden Book,” which has lots of information about Euphorbias suitable for cultivation in California and the Western U.S.
• Euphorbiaceae.org: About the Genus Euphorbia (http://www.euphorbiaceae.org/pages/about_euphorbia.html)
• Dave’s Garden: Hardy Euphorbias in the Garden — An Untamed Passion for “Shrubby Spurges” (https://davesgarden.com/guides/articles/view/373)
• Dave’s Garden: Cold Hardy Euphorbias — The Small Globoid to Columnar Species (https://davesgarden.com/guides/articles/view/2326)
• iNaturalist: Euphorbiaceae of California, US (https://www.inaturalist.org/check_lists/67883-Euphorbiaceae-of-California–US)
For gardening-related questions, call the UC Master Gardener office at (209) 953-6112, or visit our website: http://sjmastergardeners.ucanr.edu/.