Griffiths, Proceedings of the Biological Society of Washington 29(3): 13–14, 1916

Isotype; Herbarium; Herbarium; Herbarium.

Original Description

What is Opuntia caesia?

Opuntia caesia is a large, blue-green, strongly glaucous prickly-pear, typically bigger and woodier in aspect than O. phaeacantha. Colonies often span 2–3 m across and stand about 50–80 cm tall, with long, spreading basal axes and erect to ascending secondary branches.

Details

Shrubs: low, colonial to mound-forming; primary axes frequently reclining with younger growth ascending to ~50(80) cm; clumps ~2–3 m across. Cladodes: obovate to broadly obovate, commonly ~11–15 cm wide × 20–24 cm long; new joints strongly glaucous, bluish to blue-green, weathering to green or yellow-green. Areoles: moderately spaced, slightly elevated, felted, with persistent glochids and seasonal spine growth. Glochids: yellow-tan, in small clusters, persistent. Spines: usually 2–4 first-year spines per areole (more on older joints), straight to slightly flexuous, pale to dark; longest to ~5(8) cm. Flowers: yellow with red brushed on the inner segments; filaments yellow with greenish bases; style white; stigma globose, light green. Fruits: ovoid to short-pyriform, purplish-red at maturity with paler pulp. Seeds: tan, compressed (details variably reported).

Cytology

Unknown.

Range & Habitat

Northwestern Arizona (notably the Crozier–Hackberry area near Kingman and localities around Cane Beds) and extreme southwestern Utah (Rockville–St. George area). Plants occur on rocky slopes and benches, including basaltic and gravelly substrates, within open desert scrub.

Similar or Sympatric Species

O. camanchica — Often woodier and more upright, sometimes with rounder cladodes; field plants can closely resemble O. caesia, and some authors have suggested the two may be conspecific in places.

O. phaeacantha — Widespread and variable; frequently forms lower, less woody patches. Many populations lack the consistently strong bluish, glaucous coating typical of O. caesia.

Other Notes

Overall, this species is similar to O. camanchica, and perhaps the two are the same taxon. Griffiths remarked that this prickly-pear has nearly as much glaucous blue bloom as O. robusta. The bluish coat can fade toward greenish or yellow-green with age or drought. Plants are abundant near Crozier, Arizona. The degree of blue coloration varies among populations.