You can tell if the leaves are healthy by being succulent and a little glossy. This is how the leaves are transported from their parent to another place, where they become new plants. There has been debate about what species Opuntia ellisiana is a spineless form of, but most people I know have accepted David Furguson's conclusion that it is Opuntia cacanapa. Some species form clumps while others remain solitary, such as F. acanthodes, F. wislizenii, and F. acanthodes, both in the Mojave Desert and the Sonoran Desert. Here's an attempt at a rewording.