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One of the largest genera of flowering plants is Euphorbia with approximately 2,000 species. This enormous genus belongs to the very diverse Euphorbia Family (Euphorbiaceae) with at least 7,500 species. The variation within this genus is astonishing, from low-growing garden weeds called spurges to giant, cactus-like succulents that rival in size our North American sahuaro and organ-pipe cacti. South African euphorbias have evolved succulent, spine-covered stems that greatly resemble North American cacti, a biological phenomenon known as convergent evolution. It is difficult to believe that all these diverse forms belong to the same genus as the showy garden euphorbia called poinsettia (E. pulcherrima) until you carefully examine the blossom. The showy, red, modified leaves of poincettia are not petals. In fact, they are not even part of the true flowers. They surround clusters of small, greenish, cup-shaped structures called cyathia. Each cyathium is actually a flower cluster or inflorescence containing unisexual, apetalous male and female flowers. The inconspicuous male flowers occur in clusters and are reduced to a single red stamen, while the female flower consists of a single ovary (pistil) on a stalk (pedicel). In poinsettia the ovary is hidden within the cyathium, but in other species the ovary protrudes out of the cyathium at maturity. The rim of the cyathium also bears one-several, greenish nectar glands that are attractive to insect pollinators. In some species the glands are subtended by petal-like bracts (petaloid appendages). Poinsettias typically have only one greenish gland per cyathium and no petaloid appendages. This flower plan is quite different from the typical floral diagram above, but it is the basic theme in virtually all members of the amazing genus Euphorbia. It should be noted here that some authorities place the prostrate, herbaceous euphorbias (called spurges) with C-4 photosynthesis in the genus Chamaesyce.

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A dioecious species of Euphorbia called "baseball plant" E. obesa. The ovulate (female), seed-bearing plant is on the left and the staminate (male), pollen-bearing plant is on the right. Like North American desert cacti, this euphrbia can withstand prolonged periods of drought by storing water in its enlarged stem.

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Poinsettia (Euphorbia pulcherrima) in full bloom at Christmas time in southern California. Bright red modified leaves (A) surround a central cluster of greenish-yellow flower clusters called cyathia. Right: Each cup-shaped cyathium (B) contains a cluster of red stamens (D) which are the male flowers. Inside each cyathium is a hidden female flower (not shown) consisting of a single, minute ovary. The rim of the cyathium bears a greenish-yellow nectar gland (C).

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An annual poinsettia (Euphorbia cyathophora) native to the eastern United States. This species is also listed as Poinsettia cyathophora and P. heterophylla. It is commonly planted in California gardens, and often becomes naturalized by reseeding itself each year. Leaves subtending the inflorescences are bright red on the lower half. Each cyathium bears a female flower consisting of a single ovary. The rim of the cyathium bears one greenish-yellow nectar gland.

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Petty spurge (Euphorbia peplus), an erect garden weed in southern California with alternate leaves and milky sap. Originally native to Europe, this prolific seeder has become naturalized throughout North America. The urn-shaped cyathium bears crescent-shaped, 2-horned glands on its rim. There are no petaloid appendages.

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Many members of the euphorbia family, including the genus Euphorbia, contain a poisonous milky-latex sap. The toxin is a mixture of diterpene esters, and contact with the skin may cause inflammation and a blistering rash. An Australian company called Peplin Biotech is conducting research on the sap of E. peplus as a simple topical treatment for certain skin cancers, such as basal cell carcinomas and squamous cell carcinomas. These are the most common human cancers, particularly in people who spend a lot of time outdoors in direct sunlight. For years, people in Australia have used the milky sap of E. peplus to cure cancerous spots on their skin. The fresh sap from E. peplus is applied directly to the cancerous spot. After a few days the area develops into an enlarged, swollen sore, followed by a scab that eventually dries and falls off. According to Peplin Biotech, the sap penetrates the skin and destroys the malignant tissue. This is essentially what happens when a dermatologist applies liquid nitrogen directly to a superficial cancerous growth on the skin. A patent has already been applied for this remarkable discovery.

Chamaesyce polycarpa, a prostrate, native spurge that grows throughout dry chaparral hillsides in southern California. Left: Overall view of plant showing numerous cup-shaped cyathia. Right: Close-up view of several cyathia showing reddish-purple, oval glands on rim of cyathia, each subtended by a greenish-white petaloid appendage. Male flowers (stamens) are included in the cyathia, while a female flower (ovary) bearing 3 styles protrudes out of each cyathium on a long stalk.

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Chamaesyce serpens, a prostrate spurge from South America that is naturalized in southern California. A: Cup-shaped cyathium (involucre) containing minute male and female female flowers. B: Petaloid appendage extending from the rim of cyathium. C. Oval gland at the base of a petaloid appendage. D. Ovary of a female flower on a stalk that extends out of the cyathium. The ovary is glabrous (without pubescence) and develops into a multiseeded dry fruit or capsule. E. White membranous scale composed of united stipules at the base of the leaves.

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Chamaesyce albomarginata, a native spurge in the chaparral and coastal sage scrub of southern California. It is very similar to E. serpens, except it is a perennial with 12 or more staminate flowers per cyathium. The naturalized E. serpens is an annual with less than 10 staminate flowers per cyathium. In addition, E. serpens typically roots at the nodes (see previous image).

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Close-up view of the several cup-shaped cyathia of Euphorbia (Chamaesyce) maculata, a prostrate weed from the Eastern United States that is naturalized in disturbed areas and gardens throughout southern California. A. Ovary of the female flower covered with hairs, a characteristic that is necessary to identify this species. B & C. White petaloid appendage and greenish gland extending from the rim of cyathium.

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Other Species In The Euphorbia Family

Botany 110 Unknown Spurge Species A Very Painful Euphorbia With Stinging Hairs Castor Bean: Valuable Plant With Deadly Seeds The Sandbox Tree With Exploding Seed Capsules Unusual Shrubs: Tetracoccus dioicus & T. ilicifolius Economically Important Members Of Euphorbiaceae

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