Pinus johannis Rob.-Pass.

The status of Pinus johannis (syn. P. cembroides var. bicolor) is controversial – most workers recognising it as one or two full species (Perry 1991, Malusa 1992, Passini 1994, Price et al. 1998, Richardson 1998, Gernandt et al. 2003), while a few (Farjon & Styles 1997, Farjon 2005a) consider it to be only a variety of P. cembroides. This situation is exacerbated at times by difficulty in distinguishing between small herbarium specimens, of taxa that may be quite easily differentiated in the field. Some further distinctions exist between eastern and western populations of P. johannis, that have implications for horticulture. In the northeastern Mexican states of Coahuila, Nuevo León and Zacatecas, it forms only low shrubs (to 4–5 m tall), comprising P. johannis s.s. In southern Arizona and New Mexico, and in the northwestern Mexican states of Chihuahua, Durango and Sonora, however, are populations that form trees of 9–15 m, and these are treated separately by some authors, as P. discolor. In foliage and cone characters there is a great deal of overlap, and P. discolor has been placed in synonymy with P. johannis by Passini (1994). Neither P. discolor nor P. johannis is reported to hybridise with P. cembroides, with which both sometimes grow, intimately mixed (Gymnosperm Database 2007c). In foliage characters, ecology and genetics, P. johannis is more closely related to P. culminicola than to P. cembroides (Malusa 1992, Gernandt et al. 2003). Pinus johannis is in cultivation at Berkeley from seed collected in Zacatecas in 1981 by Frank Callahan, and c.1989 by L. Briones. With its low-growing, shrubby habit and attractive blue-green foliage it has great horticultural potential, especially for use in water-wise gardens. In the United Kingdom it is grown at Benmore, from collections made by Michael Frankis in Nuevo León in 1991 (M.P. Frankis 114, 179). Keith Rushforth (pers. comm. 2007) has raised Frankis 179 to 1.5 m, and there is a 1 m specimen at the Hillier Gardens, where there is also a 2.6 m plant from John Horsman dating to 1986 (2007 measurements, from Sir Harold Hillier Gardens database); otherwise, however, it is rare in cultivation.