Quercus mexicana Bonpl.

First introduced to cultivation in New Zealand, Quercus mexicana has a wide distribution in Mexico and has done well in cultivation in northern hemisphere cool-temperate gardens. Its resilience and hardiness, and the ornamental value of its youthful pachydermous bark, have made it popular among collectors. Distinguishing it from the similar Q. crassipes offers enthusiasts an interesting exercise in close observation of foliar characteristics.

In natural habitat, Quercus mexicana is found on mountain slopes and plateaus, on hillsides, next to stream beds (arroyos), on superficial or eroded gravelly or sandy soils. It is apparently not affected by soil pH and is found in association with Abies and Pinus species, notably P. leiophylla, P. montezumae, P. teocote, P. hartwegii and also P. pseudostrobus f. protuberans in Michoacán, and with other oaks, especially Q. crassifolia and Q. rugosa, and to a lesser degree Q. crassipes, Q. frutex and Q. repanda. It also grows in semi-arid habitats in pine forests in Querétaro and Hidalgo (le Hardÿ de Beaulieu & Lamant 2010).

The earliest introduction to the Old World seems to have been in 1991 by Michael Frankis, who collected it in Nuevo León. A tree from this source has grown well in the Sir Harold Hillier Gardens, Hampshire, UK, reaching 18.3 × 41 cm dbh in 2022. Trees from seed collected in 1992 by Gardner and Knees in Hidalgo have also done well in the same garden, exceeding the Nuevo León trees in diameter (44 cm in 2021), though not in height (14.3 m). Several other introductions followed in the 1990s, and the species is now well established in cultivation in Europe and North America. It has proved ‘relatively hardy’ in the UK (Edwards & Marshall 2019) and ‘surprisingly hardy’ in Illinois (Sternberg 1995). According to Grimshaw and Bayton (2009), it is characterised by vigorous new growth with brownish-red new shoots in summer and makes a slightly gawky tree that has a tendency to lean if not in full sun or staked. They recommend it for dry sunny gardens in Mediterranean climates, noting that its dull green, slightly hoary foliage combines well with many typical Mediterranean plants. A particularly attractive feature is the remarkable pachydermatous bark on young trees, though it does not last into maturity, when it becomes coarser and flakes into rectangular plates. This can be observed already on the older trees in cultivation, such as those at the Sir Harold Hillier Gardens (pers. obs. RC 2024). In Europe, a tree grown at Trompenburg, the Netherlands, from acorns received in 1992 had exceeded 10 m by 2009, though it reportedly had difficulty getting an anchor down in the wet soil there (Grimshaw & Bayton 2009).

The first introduction to cultivation occurred several years before that of Frankis, when Bob Berry collected it in 1984 in Hidalgo. A tree from this collection and another from a subsequent collection in 1986, also from Hidalgo, have grown well at Hackfalls Arboretum in New Zealand, reaching 10 m and 11 m respectively in 2004. The older tree boasted a trunk 58 cm in diameter in 2020, comfortably exceeding the largest specimens in cultivation in the UK and Europe.

It was described in 1809 by Bonpland, who found it on several locations in his travels through Mexico with Humboldt in 1803 and 1804. Their itinerary took them from Acapulco to Veracruz, traversing through several regions in Central Mexico near Mexico City. Given its apparent ubiquity, he chose for it the epithet mexicana, but it is an arbitrary choice, as several other oak species are widespread in Mexico and could lay as good or better claim to the epithet. The taxonomy of his oak has been eventful, due mainly to the fact that Trelease in his descriptions confounded this species with Q. crassipes, possibly because one of Bonpland’s specimen sheets contained both Q. crassipes and Q. mexicana. Subsequent authors followed Trelease, before Muller and McVaugh set the record straight in 1972. Though the species are similar, they can be distinguished quite easily by the tomentum on the leaf undersides (persistent and uniform in Q. crassipes, but loose and characteristically ‘dotted’ in Q. mexicana) and the venation (perpendicular to the midrib in Q. crassipes, but at an acute angle in Q. mexicana).