Griffiths, Proceedings of the Biological Society of Washington 29(3): 13–14, 1916
Opuntia caesia grows to be a larger plant than O. phaeacantha; it may reach 6-ft across and be about 2-ft tall with erect branches that rise from spreading branches. Pads are typically 4-5 inches wide by 6-8 inches long, though they are variable. The pads may narrow to a stipitate base. New growth is glaucous and blue-green but becomes green or yellowish-green in age. There are 2 to 4 spines the first year that are often dark (except for pale downward sloping spines). Longest spines can be 3-inches long. Old spines may be more numerous and are pale. The style is white and the stigma is green; filaments are yellow with greenish bases. The ripe fruit is purplish-red but the pulp is lighter. Griffiths remarked that some plants have nearly as much glaucous blue bloom as O. robusta. See the original citation.