is a huge genus (including chollas and prickly pears) within the cactus
family and differs from other cactus groups
in four main ways:
have glochids, those "nasty," barbed, brown, brittle, hairlike spines
that you often have to use glue to get out of you.
have leaves, at least for a little while, on new segments.
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
unlike the shiny black seeds of other cactuses, Opuntia seeds have
a tan covering.