Opuntioideae are unique among cacti for lacking in the stem a thick cortex, an extensive system of cortical bundles, collapsible cortical cells, and medullary bundles. Typically, the epidermis consists of a single layer of irregularly shaped cells, a cuticle at least 1-2 microns thick, and long, uniseriate trichomes in the areoles.
Opuntioideae differ from other cacti by not having a thick cortex in their stems, an extensive system of cortical bundles, collapsible cells, or medullary bundles. Typically, the epidermis consists of a single layer of irregularly shaped cells with a cuticle at least 1-2 microns thick and long, uniseriate trichomes within areoles.