No synonyms are recorded for this species name.
Euphorbia guillauminiana is endemic to Western Madagascar, in particular to the District of Analalava in the Port-Bergé area. Its distribution area is reduced, extended for an area of occupancy of around 90 square kilometers. The habitat of this species are mainly basalt rocks in warm climates, and it is threatened by human activities, including illegal collection.
E. guillauminiana is an odd shrub, up to 1 meter tall, made of thick wooden branches equipped with sharp spines and succulent leaves arranged in tufts at the top of the wooden stems. The main trunk is very thick and branches out immediately above the ground, at around 10 centimeters from the soil surface, to rebranch at smaller intervals. The branching arrangement is dichotomous: this means that the angle the angle between two branches is 90 degrees. The overall plant, due to the thickness of the trunk and the dichotomous ramifications, looks decorative and compact, making the perfect bonsai. Its enlarged stem has the function to store water and nutrients to survive droughts and itis called “caudex”.
Leaves, instead, are dark green, oval, glossy, equipped with a short petiole, crowded at the top of the branches, arranged in tufts. Their extremely elegant glossy surface has the function to protect them from evapotranspiration and reduce the water loss. They are deciduous and fall uring the dry season.
Under the leaves, sharp wooden spines grow: they are arranged in 2 to 4 for each node, are sometimes forked and have an enlarged base.
The inflorescences are called cymes: a cyme is a flat-topped inflorescence in which the central flowers open first, followed by the peripheral flowers. A cyathium (cyathia in the plural form) is one of the specialised false flowers forming the inflorescence of plants in the genus Euphorbia. In E. guillauminiana there are 2 to 4 cyathia for each cyme. The cyathia are enveloped by special structures that look like the petals of regular flowers, called cyathophylls, that, in this species, are yellowish green or yellow.
Euphorbias are, in general, tough plant and easy to grow. However, among them, E. guillauminiana is quite a difficult species. Here below are our tips:
Put it in a bright spot, though avoid direct sunlight during the hottest hours of summer days. Prefer filtered or indirect light.
Keep it a temperatures above 5-8ºC, since this species is among subtropical Euphorbias and is more cold-tolerant. Make sure its substrate stays completely dry during the Winter to avoid rotting.
Water abundantly but unfrequently in Spring and Summer, during the growth season, waiting for the soil to dry up completely before each irrigation. In Winter and Autumn, suspend watering.
Choose a very well-drained soil: a mix for succulents should do good.
Fertilize once a year with a product rich in Phosphorus and Potassium and poor in Nitrogen. Dilute the product to half the doses recommended on the label.
Repot whenever the plant outgrows its pot. Choose pots that are only slightly larger than the diameter of the plant, like 1 or 2 centimeters wider.
Propagation of Euphorbia guillauminiana and, in general, of Euphorbias, can be carried out both by seed and cuttings. In this case, you would have to use branch wooden cuttings. Before planting them, wash with warm water to remove the latex, let them dry for a couple of days and then replant in a light, sandy substrate that should be kept moist until it has put roots. You’ll have to wait around a month until this happens. We recommend to help yourself with a rooting hormone. Seeds are rarely used, also because this species has a low percentage of autofertility and sed production is scarce. We suggest to try to carry out cuttings to replace eventual losses.
The latex of Euphorbias is often used in pharmaceutical industry because of its medicinal effects.
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