Description
Opuntia pottsii var. montana (firstly described as Opuntia cymochila var. montana by Engelmann & J.M.Bigelow in 1856) is a mountain form of Opuntia pottsii (Opuntia macrorhiza subs. pottsii). The key difference by which var. montana was separated from var. pottsii, namely the joints mostly wider than long usually dark to somewhat bluish green, weakly or not narrowed near base (stipitate), the spines usually white, the fruit mostly chunky and short, usually pinkish, the root tuber globose usually without rhizomes, and the flowers usually pale yellow and red in centre, seems entirely spurious, but plants from the areas above 1800 metres do differ in various respects from that found at lower elevations. However the distinguishing characteristics of var. montana, appear to fall within the natural variation of Opuntia pottsii and it should be synonymized with the latter.
Habit: Shrub to 30 cm high.
Root: Root tuber globose, oozing a white sap if injured, and usually without rhizomes.
Stem segments: Upright, fleshy, obovate to round, mostly wider than long 5-13 cm long, waxy dark to somewhat blue-green, weakly or not narrowed near base (stipitate).
Glochids: Yellow to reddish brown.
Spines: 1-4 per areole in upper part of the pad, erect to spreading, whitish, greyish, or shades of rust, often needle-like, but may be flat or twisted.
Flowers: 5-9 cm long, 4-6 cm wide, usually pale yellow and red in centre, but also, yellow, orange, magenta, pink or salmon. Stigma-lobes white to cream colored.
Fruits: Fleshy, mostly chunky and short, 2.5-5 cm long, 2 cm wide, pinkish purple.
Chromosome number. 2n=44.
Origin and Habitat
New Mexico and Texas, USA
Habitat and ecology: Opuntia pottsii var. montana is usually found in areas of conifer or oak woodland above 1800 metres, occasional in grasslands at lower elevations.
Cultivation and Propagation
Opuntia pottsii var. montana is a relatively difficult to grow so it is seldom cultivated for the horticultural trade.
Soil: Requires a sandy or very well-drained soil. Prefers a neutral to alkaline soil.
Moisture: Plants must be kept rather dry in the winter but they like a reasonable supply of water in the growing season. A position at the base of a south-facing wall or somewhere that can be protected from winter rain is best for this plant. Plants endure considerable abandon. Exposure Requires plenty of sun.
Hardiness: Is is quite cold tolerant plant, it can succeed outdoors. Said to be hardy in Zones 3 and 4 (USDA)
Bibliography
Major references and further lectures
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David J. Ferguson “Keys to the identity of cacti of the Albuquerque & Santa Fe area (Bernalillo, Sandoval, Santa Fe, Socorro, Torrance, and Valencia Counties)” November 1993 (updated May18, 2012)
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Jean-Luc E. Cartron “A Field Guide to the Plants and Animals of the Middle Rio Grande Bosque” UNM Press, 2008
3)David J. Ferguson “Chromosome counts on DJF collections of Cactaceae” retrieved 22 March 2016 from <http://opuntiads.com/records/chromosome-numbers-cacti-djf.pdf\>