Euphorbia caput -medusae is somewhat similar to the more robust Euphorbia tuberculata with similar flowers. Judging from the specimens I have the tubercles of Euphorbia caput -medusae are not as pronounced as the one of Euphorbia tuberculata. Euphorbia caput -medusae bears its cyathia almost right to the tip of the fingers while in the case of Euphorbia tuberculata the cyathia are more to the side. Peter Bruyns has both these 'species' and some others that are even more different included under Euphorbia caput -medusae. I keep the names separate for practical reasons.
This is a seedling of one of the largest growing "Medusa Head" Euphorbias of South Africa. Their natural habitat is on the Cape Penisula, a high rainfall area.