Euphorbia polyacantha aka Fishbone Cactus

Euphorbia polyacantha is a spiny shrub in the Euphorbiaceae family. It is a succulent, a plant that stores water. Its common names include fish bone spurge and fish bone cactus. It is native to northeastern tropical Africa and southern Yemen. Records list Sudan, Eritrea, Ethiopia and Somalia. It grows on rocky slopes and outcrops in dry country. It lives in open bushland and at lower juniper forest edges. It also grows in shallow soils on dry savannah hills.

Plants tend to reach 3.3–4.9 feet (1–1.5 metres) tall. Some reach 6.6 feet (2 metres). The shrub grows wider than tall and has no clear trunk. Many upright branches grow from near the base. They form a thick crown, with a rounded or near-flat top. The plant stays green but has no leaves. Its smooth stems range from grey-green to dark green. Each stem has four to seven angles and shallow, oval sections. Small, rounded teeth line the edges. These edges bear dark spine shields that join together.

Dark grey spines grow in pairs along the stem edges. They spread apart and may curve upwards. Small yellow-green flower parts grow between these pairs. These parts, called cyathia, grow alone or in groups. Each group has up to four. Each cyathium forms a cup with five glands. It also has five lobes with fringed edges. The fruit is a small capsule with three lobes. It turns dark purple-black or brown as it ripens. The seeds stay very small, with grey, rough, oval forms.

People grow this shrub in home gardens for its shape. They also plant it as a living fence. Other plantings help keep soil in place. Cuttings root with ease, but fresh cuts need time to dry. Useful Tropical Plants says to wait several days before planting. Keep the cuttings in light shade during that time. It calls for soil that drains well. Planting cuttings before the cut ends dry can cause rot. The sources give no firm frost limits or bloom season.

Useful Tropical Plants lists no food uses for this plant. It reports local use of crushed stems on scorpion stings. This is a folk practice, not proof of safe treatment. People also mix crushed stems with water to fight crop insects. The supplied accounts give no toxicity data for this species. Useful Tropical Plants gives a warning about safety for the wider genus. That warning does not rest on confirmed findings for this species.