Euphorbia esculenta is a succulent Euphorbia from South Africa in what is called the 'medusa-head' group. (To refresh your memory, Medusa is a Greek mythological character with a head of snakes.)  'Esculenta' actually means 'edible', presumably only by some animal, or maybe this is just a nomenclatural quirk, of which there are many in the plant world.  In any case, all euphorbias have caustic sap, a milky latex that if ingested would cause burning of the esophagus and painful burning if gotten in the eyes.
E. esculenta can grow to a diameter of three feet, but in containers usually is much less.  The plant above is in a 10" diameter pot.  They grow best in some shade, but not dense, and will tolerate temperatures right down to freezing, if only for short intervals.  This species is primarily a warm season grower, with flowering taking place in spring.
Some euphorbias are dioecious (male and female flowers on different plants) whereas this one has complete flowers as seen in the picture below.  You can easily see the green stigma lobes and the orangeish pollen on the anthers.