Opuntia is a huge genus (including chollas and prickly pears) within the cactus family and differs from other cactus groups in four main ways:

• Opuntia have glochids, those "nasty," barbed, brown, brittle, hairlike spines that you often have to use glue to get out of you.
• Opuntia have leaves, at least for a little while, on new segments.
• Oputia stems grow in jointed segments and each segment only grows for one growing season (terminating with the beginning of the dry season). New segments grow from the areoles of previous segments. Stems of other cactuses are not jointed and continue to elongate their whole life (indeterminate growth) or until damaged.
• Finally, unlike the shiny black seeds of other cactuses, Opuntia seeds have a tan covering.