Picea chihuahuana Martínez

Picea chihuahuana was described in 1942, having been found earlier that year near Talayotes, in the eponymous Mexican State. It would not be introduced to cultivation until some time later, perhaps as late as 1984, such that it gained an entry in New Trees where it was described as ‘one of the most notable of recent tree introductions […] certainly a species that should be grown more frequently’ (Grimshaw & Bayton 2009).

In its vegetative details at least, Chihuahua Spruce bears a strong resemblance to Picea pungens, distributed further north in the American Rockies. The seed cones are quite different though, and in this respect P. chihuahuana perhaps most strongly resembles P. polita of Japan, but molecular studies have been inconclusive regarding its placement. Ran, Wei & Wang (2006) found it was not closely related to any other North American spruce, but nested within a group of species otherwise distributed in the Himalaya and eastern Asia; those authors considered this could only have been achieved via a back-dispersal event they themselves considered highly unlikely. A close relationship with another Mexican endemic, P. martinezii, has long been inferred (some authorities, notably Farjon, considered P. martinezii synonymous with P. chihuahuana until Taylor, Patterson & Harrod (1994) proved it was distinct). P. chihuahuana and P. martinezii have in common many aspects of seed cone morphology, although P. chihuahuana has larger cones, but one of the most complete phylogenies of the genus suggests they are not particularly closely related whilst also refuting the suggestion of close affiliation with any Asian taxa (Lockwood et al. 2013). Other studies have found P. chihuahuana sister to P. pungens, possibly representing an ancient lineage within North American spruces which perhaps contributed their genes to a later radiation to Asia rather than having back-dispersed from it (Shao et al. 2019).

Whatever its true phylogenetic position Picea chihuahuana is most likely to be confused with P. pungens. Vegetative details separating the two include the laterally compressed, much more rigid, much more sharply pointed needles of Chihuahua Spruce, which, particularly on young trees, will merrily draw blood, while those of P. pungens will do little more than prickle uncomfortably, being more flexibly attached to the pulvini. The seed cones are quite different; much larger in P. chihuahuana and with the exposed part of the scale rounded and entire rather than rhombic to deltoid and emarginate in P. pungens (Earle 2024; Debreczy & Rácz 2011).

Keith Rushforth introduced material to British cultivation in 1984. This was supplemented in 1989 by Hjerting & Ødum 12 which is represented in several arboreta in the UK and Denmark, notably Benmore Botanic Garden and Mount Stuart (both Argyll, UK, characterised by mild, very wet climates) and Tregrehan, Cornwall (also mild and wet) where a tree planted in 1994 was 6 m tall × 14 cm dbh in 2024. Other introductions by Frank Callahan, in the late 1980s and early 1990s, may be the source of some of the oldest trees in North American arboreta, notably a tree in Fichtner-Mainwaring Park, Medford, Oregon, which was ‘about 7 m tall when seen in 2004, growing vigorously, with a perfect shape from its regular, densely clad branches’ (Grimshaw & Bayton 2009) and others at the Arnold Arboretum, an entirely different climatic zone which demonstrates the species’s adaptability. When seen during research for New Trees the four Arnold trees were ‘flourishing trees of about 4.5 m (in 2006)’ (Grimshaw & Bayton 2009) and by 2025 the best were perhaps nearly double this size (pers. obs.).

In recent years seed from the tree at Fichtner-Mainwaring Park has been grown and distributed in the UK by Bedgebury National Pinetum. Whilst the possiblity of hybridity must be acknowledged, the progeny so far bears a strong resemblance to Picea chihuahuana and have proven highly adaptable across a range of UK collections, although none are yet known to have produced cones. A tree at Murthly Castle, Perthshire is thriving in a sunny but sheltered position on alluvial soils; in its vegetative details it resembles P. chihuahuana exactly but its vigour is remarkable to the point of being suspicious (pers. obs.).