As you make your way up the winding path to the top of Heidelberg Hill in the Garden’s Mediterranean collection, you will find yourself amongst the branches of a striking evergreen shrub with a sweet ambrosia scent. This plant is Euphorbia mellifera, more commonly known as the honey spurge. This architectural shrub is native to the Canary Islands, an archipelago in the Atlantic Ocean off the coast of northwestern Africa. This shrub tolerates heat and drought but will not survive cold or wet winters. Luckily, that means it happily thrives in San Francisco because of our Mediterranean climate!
Over 2,000 spurges exist worldwide in a diversity of life forms from annual or perennial herbs, to cactus-like succulents found in the deserts of southern Africa, to the well-known poinsettias found in the tropical forests of Mexico.
The species name mellifera means "honey-bearing" and refers to the sweet honey-scented flowers that adorn the end of its branches. Euphorbias have highly unusual flowers. The flowers are imperfect, or unisexual, meaning their male and female reproductive parts are found on separate, individual flowers. The female flowers have the ovaries tethered to the flower like a ball on a rope in a unique structure called a cyathium. The male flowers are reduced to a cluster of their stamens, which bear the pollen. These flowers lack the petals or sepals that are typical of most flowers in other kinds of plants. Instead, the euphorbia flower's reproductive parts are supported underneath by bracts that have evolved to attract pollinators the way petals do on other flowers. Look closely at these modified flowers to see if you can tell the difference between the males and females!
Take care when handling any euphorbias as all plants in their family produce a milky sap called "latex" that will irritate your skin. Don't be put off though-this sap helps protect them from herbivory, keeping your plant looking beautiful and pest-free.
Euphorbia mellifera makes an excellent specimen plant as well as a large evergreen backdrop to display smaller plants against. It is even rumored that euphorbias can act as gopher deterrents! Prune back this shrub's flowers to encourage increased vegetative growth or leave them to bloom so you can enjoy their odd floral display and sweet fragrance.
IN BLOOM CONTRIBUTORS: Text and profile by Sarah Callan. Photos by Joanne Taylor, Mona Bourell, Sarah Callan and Brendan Lange.