Very common shrubby succulent Euphorbia from Madagascar. Stems are 4-5 sided, with bristles along the ribs and pale leaf scars. Leaves on young plants have prominent white veins (thus the species name), but these are mostly absent on older plants. The cyathia appear close to the tip and are short and brownish red, with bright white exserted stamens and styles.
This species does better in relatively low light (for a succulent) compared to many other Euphorbias and enjoys more water than many desert plants. It is self fertile and may produce an abundance of volunteer seedlings scattered about at some distance from the mother plant.
For several months I have observed small striped, green leafed plants emerging in some of the pots in my sun room. I didn't know what they were or how they got there. Tried using "Picture This" app on my phone to learn what they were and how they may have planted themselves. Turns out that they are babies from a plant given to me by a friend who didn't know the ID of the plant. It's a Madagascar Jewel (Euphorbia leuconeura). The mother plant is about two feet tall and the leaves are plain green, not striped, so I didn't understand the connection between mother and babies. Best of all, I learned that when the seeds are ripe, they explode to nearby territory. I'm waiting to observe one of these explosions but in the meantime I will pot up the babies to give to friends.
I have now witnessed an "explosion" of seeds from this plant. I was sitting in my sun room reading and saw seeds from this plant scatter over the floor and into a few nearby pots. Too cool! Now, I will have more baby plants to give away.
but in the meantime I will pot up the babies to give to friends. 
