Euphorbia canariensis is known by the common names Canary Island spurge, Hercules club and cardón. It is a succulent member of the Euphorbia subgenus Chamaesyce section Anisophyllum in the family Euphorbiaceae. It's endemic to the Canary Islands where it is the plant symbol of the island of Gran Canaria.
Hercules club is a small succulent shrub that grows 9-13 feet high. It clumps profusely at the base and a trunk may produce more than 150 branches as thick as a man's arm.
Stems are stout and fleshy, highly succulent, columnar, upright, and cactus-like. They are deep green to reddish in color with four to six angled surfaces and are slightly spiral. They have a smooth surface. The edges are obtuse and brownish in color. The lateral branches form an angle at the base, but are straight after that. The plant has pairs of dark, shiny spines. They are regular and straight to cow-horn shaped, spreading laterally in rows along the four corners of the columns.
Hercules club blooms are red to reddish-green in monoecious heads surrounded by an involucrum consisting of 1 leaf with 5 divisions that have 5 alternating glands. Male flowers are monandrous with their pedicel surrounding the female which is in the center. The female flowers are naked and solitary with a stalked ovarium. The stigma is three-forked.
This species is also widely used in the horticulture trade as a strong and long-lasting grafting stock for many rare, slow-growing, sensitive species of Euphorbia. Most people are unaware of just how large this succulent can grow. That characteristic should be considered when planting since Euphorbia canariensis is often planted in places where it can cause problems later.
As with all Euphorbias, a plant that has been injured exudes a thick, white, milky sap known as latex. This latex is poisonous and may irritate skin. Caution should be taken when handling any Euphorbia plant to avoid getting any of the sap in your eyes or mouth. Handle with care.
The plant reproduces by seeds or cuttings. Since it branches prolifically, offsets are usually readily available on older pants. Before beginning propagation, wash the cut to be sure the latex sap has been removed. After you remove an offset, let it dry for several days to a week in order for the cut to heal. Cuttings planted too soon will rot before they can grow roots. You can lay cuttings on top of the soil and insert the stem end partially into the substrate. Try to keep the cutting as upright as possible so the roots are able to grow downward.
Although all cacti are succulents, not all succulents are cacti. Most Euphorbias are succulents. Many of them look like a cactus and are typically referred to as “euphorbia cactus”. But no Euphorbia is biologically a true cactus. When in bloom, differentiating is easy. The flowers of cacti are complex and typically large and flamboyant. The flowers of a Euphorbia are quite small and simple with either only female or only male parts to each flower.
Most Euphorbias like dry, well-drained soil and are very useful for dry spots where many other plants would struggle. E. palustris prefers moist shade. The roots make a potato-like lump above the surface and from this grow very vigorous 3-foot stems in spring. These have a characteristic flush of yellow flowers at bloom time. They are not actually flowers but are bracts, or floral leaves, surrounding the tiny, insignificant flowers. These leaves are smaller and a different shape than the true leaves. They provide the main decorative effect of most Euphorbias. E. amygdaloides has russet leaves. E. griffithii blooms are orange or yellow. It will also do well in heavy soil and some shade, although it prefers sandy, sunny conditions. When ideally situated, it can become too vigorous for a confined space. Heavy soil can act as a useful containment for its natural tendency to spread. Like all succulents, Euphorbias do best with a fast-draining soil that is nutritionally lean.
Technically, the actual flowers of a Euphorbia are small and nondescript having colored bracts beneath and with long stems. Hercules club can create an architectural effect in the garden and is a good accompaniment for some of the showy flowers in the summer garden. Euphorbia canariensis is used primarily for its foliage effect, and since the flowers are more subtle, they are a choice plant to use among more colorful flowering plants to provide interest in the garden and also provide a depth that flowers alone can't achieve. All Euphorbias belong to the same genus as the Christmas poinsettia, illustrating just how large and varied this genus is.
Concerning pets and wildlife, no dog will willingly eat enough Euphorbia to get very ill from it without vomiting. Hercules club is also deer-resistant.
The plant is traditionally used in the Canary Islands for fuel after it has been dried. A large plant can provide enough wood for one person for the entire winter.