Taking advantage of the fact that the Euphorbia obesa are blooming, I am going to show with photos the way to differentiate a male from a female plant, a very common doubt since the flowers are very small and not very showy.
The Euphorbiaceae have the peculiarity of giving inflorecencias of type cyathia , so that what we see as a single flower, in reality is a set of flowers with special characteristics.
In the masculine plants the cyathia consist of numerous flowers reduced to a single stamen. The appearance is of a handful of stamens with pollen, as seen in photos 1 and 2. The stamens are easily detached, in the pictures some have already left.
In female plants the cyathia is composed of a tricarpelar ovary, with three bifid stigmas or pistils, as if they were three green snake tongues (in a crazy rapture of imagination).
Photos 3 and 4 show the three little arms emerging from the ciato. These do not detach easily like the stamens, and at first sight they are distinguished because, obviously, they do not have pollen.
To distinguish if the view fails, you can use a magnifying glass or a digital camera with macro. But it also serves to take a photo as close as the focus allows with maximum resolution and then enlarge it on the computer. Anyway what I found most useful is to gently move your finger over the flowers and see if yellow dust (pollen) or stamens fall. In that case insurance is a male plant.