This is the Euphorbia everybody knows. Euphorbia pulcherrima, a "weed" originally bought into the house as a Christmas decoration in Mexico, is now the most commercially important plant on the planet. Named for Joel Roberts Poinsett, who grew these in his South Carolina greenhouse. Commercially, the stems are infected with a phytoplasma, a plant tissue parasite, causing the plant to form multiple red "heads".
Many of the kitchen windowsill "cactus" are not a cactus at all but a Euphorbia or Spurge. Some Euphorbiaceae are tiny plants seen in cooler places like UK woodland; some are huge, African tree species that defy drought.
HOMESURREY'S WILDFLOWERING PROJECT is a community-led initiative, aiming to build a partnership that enables wildflowering in the county as well as promoting and celebrating the boroughs/districts diverse environments. Do take the time to find out more about the project and if you can get involved, even in a small way, you will make a difference.