Euphorbia polyacantha subsp. rosenii
Euphorbia polyacantha is native to Eritrea, Ethiopia, Somalia, Sudan and Yemen where the plant grows on mountains and valleys and can spread up to 2200 m of altitude.
Euphorbia polyacantha is a spiny bush belonging to the Euphorbiaceae botanical family. The succulent has an erect habit and can reach up to 2 m in height. The stem is short and sometimes absent, the branches are erect and numerous. The stem and the braches are greenish-grey, quadrangular, arranged in 4-7 well-defined ribs. The margins of the branches are greyish, covered with the spines. The spines are short, curved upwards in pairs and are dark grey in color. Cyathia are the typical inflorescence of the Euphorbia, it is an inflorescence consisting of a cuplike cluster of modified leaves enclosing unisexual flowers. This species has small, light yellow to green cyathia normally being all male on some plants, or all female on others. Because there are male plant and female plant, cross pollination is required that is normally carried out by insect. Blooming occurs during the spring and the flowers emerge between the spine pairs. The fruits are purple brown and containing rough grey seeds.
The plant has a slow growth rate but it easy to cultivate. The best sun-exposure is in bright place but is recommended to avoid direct sun-light in the hottest periods. The minimum temperatures that the plant can withstand are 8° C, below this temperature it begins to suffer so it needs to be placed indoors in the coldest periods. The perfect soil is a well-drained soil that let the water to drain away and avoid root rot. To achieve this feature, you can mix the pumice soil, clay and soil. Using a perforating pot, you can drain excess water. Watering is very important for this species and should be done well: during the vegetative period you can water the plant (every 7 days), checking that the soil is completely dry before watering again; in winter you should stop the watering to allow the plant to enter dormancy. About fertilization, for this plant is sufficient to fertilize moderately during the growing season with the specific fertilizers for succulents and stop fertilizing during the winter. You should repot the plant every 2 years in a pot 2 cm wider. Repotting should be done early in the growing season with fresh new potting soil. Be careful to red spiders and mealy bugs.
Propagation can be done by cutting or by seed. By cutting you can make the cut during the spring and then let the cutting dry; after a few days the cut surface will dry and a callus will form, then place the cutting in a mixture of sand, soil and pumice. To increase the success of propagation you can make two or more cuttings at the same time. For cuttings it is recommended temperatures around 20 °C. By seed it is very simple to propagate the plant, it is enough to sow the seed in a sandy loam soil and keep it with a high level of humidity and at temperature of 14 C°.
Species of the Euphorbiacee family normally if are damaged, exude a white milky sap, called latex. Many plants produce latex, but in the Euphorbiacee this latex is often poisonous and may irritate skin. The poisonousness is due to some alkaloids so it is best to keep the plants away from children or pets. The stems of the plant are used in Sudan to treat scorpion stings. The specific epithet come from Latin and means “with many spines”.
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