AbstractDetermination of the main structural features of the mucilages from Opuntia monacantha, Opuntia nopalea‐coccinillifera, Cereus peruvianus and Wigginsia erinacea by hydrolysis and methylation indicated that these polysaccharides have some similarity to both pectic polysaccharides and gum exudates, and, consequently, may provide an alternative source of industrial raw materials. The chemical composition of the mucilages is consistent with a role in the storage of moisture in Cactaceae and may be used to provide a useful method of taxonomy within the family.