This is Senecio madagascariensis. In Hawai‘i it is referred to as fireweed but sometimes it is also called Madagascan Ragwort. Although quite beautiful, this is actually a deadly weed, producing chemical toxins which can kill cattle and horses. Some animals, like sheep and goats, can tolerate it better, but they too can be affected through long-term exposure. Fireweed occupies hundreds of thousands of acres— and the size of the infestations is growing.