Euphorbia xanthadenia is a rare, disputed species from southern Madagascar.
Description Euphorbia xanthadenia is a mound shaped plant usually growing 70–100 centimeters tall, though on occasion growing as tall as 150 cm, with a width of about 100 cm. It is a succulent species with an appearance somewhat like a small tree with the main stalk and branches covered in 0.5 to 1.5 centimeter long thorns. The narrow leaves are only found near the ends of the stems and branches. The inflorescences are also found at the tips of the plant's branches.
Taxonomy Euphorbia xanthadenia was named and scientifically described in 1921 by Marcel Denis. It is classified in the genus Euphorbia within the Euphorbiaceae family. In many sources it is described as variety of Euphorbia mahafalensis following the 1946 description by Jacques Désiré Leandri, but in 2021 Haevermans and Hetterscheid supported the original description of it as a species by Denis. It is listed as an accepted species by Plants of the World Online (POWO) and the entry in the IUCN Red List is also for a species. E. mahafalensis has round branches while the branches of E. xanthadenia are angular when examined in cross section. The species has no accepted varieties, but it has six synonyms in POWO.
Table of synonyms Name Year Rank Notes Euphorbia croizatii 1946 species = het. Euphorbia ebeloensis 2017 species = het. Euphorbia emiliennae 2017 species = het., not validly publ. Euphorbia emilienneae 2017 species = het., without page number. Euphorbia helenae 2016 species = het., nom. illeg., homonym. post. Euphorbia mahafalensis var. xanthadenia 1946 variety ≡ hom. Notes: ≡ homotypic synonym; = heterotypic synonym
Range and habitat It is endemic to southern Madagascar in rocky areas of the inland mountains and cliffs.
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