This variety has longer and thicker leaves than the other two (14–25 × 0.14–0.18 cm) and cones with thinner, flatter scales. There are 8–12 lines of stomata on the lower leaf surface. Farjon & Styles 1997. Distribution MEXICO: southern Coahuila, southern Nuevo León, San Luis Potosí, Zacatecas. Habitat Similar to that of the type variety, though often more arid and at lower altitudes. USDA Hardiness Zone 8. Conservation status Not evaluated. Illustration Farjon & Styles 1997.
Pinus arizonica is closely related to P. ponderosa, but has a more graceful appearance due to its more slender growth and finer needles. No mature examples of var. arizonica were seen in the research for this book, but there is a handsome young specimen on the lawn near the Main Gate at Kew, forming a neatly conical tree of 8–9 m in 2007, with branches to the ground. This was grown from seed collected in the Sierra Madre Occidental in Chihuahua in 1993 by an expedition from the Royal Veterinary and Agricultural University, Hørsholm, Denmark. A plant from the same collection at Arboretum Wespelaar also made an elegant tree, of 6 m, but is unfortunately suffering from dieback at present, caused by the fungal pest Sphaeropsis sapinea (K. Camelbeke, pers. comm. 2007). With its dark green, upward-pointing needles densely covering the branches this is an attractive tree, at least when young (images seen on the internet suggest that it becomes much more open and gaunt with age). It is also grown at Wakehurst Place, from material collected in Chihuahua by Peter Catt, but is less common in cultivation than var. cooperi, at least in the United Kingdom (although none of the varieties are likely to be found outside specialist collections). Var. cooperi has been grown in Britain for some time longer, having been included in the 1962 introduction of several Mexican conifers to the Forestry Commission (Mitchell 1972). There are large individuals in a number of collections, including two trees at Westonbirt (15 m in 2002), and some good specimens at Bedgebury.
Var. stormiae was introduced to cultivation by Michael Frankis on his 1991 visit to Nuevo León (under the numbers M.P. Frankis 143, 163), and trees from this source are growing at Benmore and elsewhere. The cones are quite different from those of var. arizonica, and the taxon may be better treated as a distinct species, as suggested though not validly published by Gaussen (1960); it is also distinct in its long, twisted glaucous grey-green leaves. It is curious that P. arizonica and its varieties have generally slipped by the attention of horticulturists in both Europe and North America, as they appear to be attractive and hardy pines.