Quercus crassifolia Humb. & Bonpl.

Quercus crassifolia is easily recognised by its leaves: stiff and leathery, glossy blackish-green above, covered with pale brown hairs beneath and bearing bristle-tipped teeth above the widest part of the leaf. The species was first collected by Alexander von Humboldt and Aimé Bonpland on their famous five-year journey to Latin America at the cusp of the 18th and 19th centuries; the name was published by Bonpland in 1809, thus making this species one of the first Mexican oaks to be described (several species were described by Luis Née in 1801). It is a relatively common species in suitable locations in central and southern Mexico. Some plants from further north in Sonora, Durango, and Chihuahua previously thought to be this species may be the related Q. mcvaughii, described in 1992, which differs in having sessile rather than stipitate hairs on the leaf undersides. Quercus fulva has trichomes with straight rather than tortuous rays, while Q. calophylla has thinner leaves with more numerous teeth and a white tomentum (Coombes 2012).

One of the attractive features of this oak is the new growth: leaves emerge densely covered in velvety red hairs and are silvery and tomentose beneath. As they mature the leaves turn a glossy dark green, becoming coriaceous and rugose with impressed veins. The tree is deciduous or semi-evergreen in the wild, losing its leaves just before the new ones emerge, but in cultivation it appears to be evergreen. In the wild it flowers in April and the acorns ripen in May to November, in the following year.

Quercus crassifolia hybridises with several other Section Lobatae species in the wild, especially Q. crassipes to form Q. × dysophylla. Other less frequent hybrids are found with Q. affinis, Q. candicans, and Q. laurina.

It grows in several gardens in the UK, having been introduced in 1934 (not 1939, as reported by Bean) by George Boole Hinton (1882–1943), a British metallurgist who decided that his calling was in the botanical exploration of his adopted home, Mexico (Hinton & Rzedowski 1972). One of the original trees, grown from Hinton 6402, survived at Caerhays and measured 12.5 m × 69 cm in 1971 (Bean 1976) but suffered severe dieback and was 8 m tall in 2006; it is now recorded as lost on the Tree Register. The tree at Kew reached 16.5 m × 72 cm in 2022. The accession number suggests the seed was received in 1934 and, according to Tony Kirkham (pers. comm. 2024), it was planted in 1936. This suggests it is also a Hinton introduction, possibly the same one as the Caerhays tree. According to E.F. Warburg (1939), Hinton collected seed of this species between 1933 and 1936, and Hinton 6402 was collected in July 1934. However, it seems the tree currently at Kew was planted later. Alan Mitchell, in the 8th Edition of Bean (1976), stated the tree was ‘very vigorous’ and younger than the tree at Caerhays, with a dbh in 1976 of only 15 cm. Measurements since then do confirm vigorous growth (23 cm dbh in 1982, 48 cm in 2001, and 72 cm in 2023), but suggest a planting date around 1960. According to Owen Johnson (pers. comm. 2024), Hatton Gardener recorded a smaller tree at Caerhays (6 m × 8 cm in 1966), which no longer exists. This raises the possibility of either a second introduction or that the younger trees at Caerhays and Kew were grown from seed obtained from the original tree at Caerhays.

At Chevithorne Barton (Devon, UK) a tree from seed collected in 1995 by Silvia Romero Rangel in Michoacán at 2,700 m (ROMR 5100) was planted in 1997 and measured 9 m × 30 cm in 2017; another tree, of unknown origin, planted in a sheltered position, reached 10 m in about eight years and measured 15 m × 26 cm in 2017. At Buckingham Palace, another tree grown from ROMR 5100 had grown to 15.3 m × 23 cm in 2021 (Coombes 2012, Heathcoat Amory 2009, The Tree Register 2024).

Three trees grow at Penrice Castle in Wales: one, from seed collected in 2007 of unknown origin, had reached 6 m in 2021; the other two are from seed collected by Allen Coombes in 2008 in Puebla at 2225 m (CMBS 1165) (T. Methuen-Campbell, pers. comm. 2021). Another introduction to the UK was from seed collected by John Fairey of Yucca Do Nursery (Texas, USA) in 1993 in Nuevo León at 2180 m. Seed from this source, received as Q. tomentella, was distributed by Maurice Foster and later determined to be Q. crassifolia; trees grow at White House Farm, Kent (planted 2001, 16 m × 26 cm in 2019, the origin of the cultivar ‘Flamingo’, see below), at Tregrehan, Cornwall (planted 1996, 13 m × 13 cm in 2014), and at Wakehurst (planted in 1993, 19 m × 34 cm in 2022) (The Tree Register 2024).

Elsewhere in Europe it is found at Arboretum des Pouyouleix, France, from seed collected by Paco Garin in Guerrero in 2004, planted in 2008 and measuring 13 m × 19 cm in 2021 (B. Chassé, pers. comm.); one of the two trees from this accession produced spectacular growth in 2014, putting on more than 2 m in the growing season (Chassé 2014). At Iturraran Botanic Garden, Spain, there are four trees from seed collected by Paco Garin in the southern part of its range (Chiapas in 2003 and Oaxaca in 2004). At Arboretum de la Bergerrette, France, a tree grown from seed collected by Allen Coombes in 2009 appears to be Q. × dysophylla, despite having been collected from a tree that was unequivocally Q. crassifolia, showing that even seed collected in the wild can turn out be hybridised, as is often the case with seed of garden origin.

In the US it grows well at the John Fairey Garden, Texas, which is not far from the species’ range in Mexico, but has also survived at Aiken, South Carolina, despite being badly damaged by frost in 2017 (Russell 2017). On the west coast it grows in northern California: a plant of wild origin from Mexico grows in San Francisco Botanical Garden (San Francisco Botanical Garden 2024), and at UC Davis there is a tree grown from seed collected in 1966 by Lance McIntyre and Dick HIldreth in Guatemala, the only record we have found in temperate zone cultivation of Q. crassifolia of Guatemalan origin (Quercus Multisite 2021).

But by far the most significant instance of this species in cultivation is at Hackfalls Arboretum in New Zealand. A total of twenty two Quercus crassifolia grow there, from fifteen different seed-raised accessions collected by Bob Berry between 1982 and 1989 in five Mexican states (Chiapas, Hidalgo, Mexico State, Michoacán, Oaxaca, Puebla, and Tlaxcala). Not all these trees have been measured, but one, from seed collected in 1984 near Topeligo, Tlaxcala, measured 20.2 m × 76 cm in 2022, making it the champion tree for height recorded in cultivation. Other trees at Hackfalls have larger dbh values (up to 88 cm), but their height has not been recorded (Hackfalls Arboretum 2024, E. Cairns, pers. comm. 2022). At nearby Eastwoodhill Arboretum, another ten trees are listed, with accession numbers starting in 1987, presumably also from Bob Berry collections. The species has also grown well at Mereweather Arboretum, Australia (Funk 2015).

The wood of this oak is used in Mexico for the manufacture of agricultural implements and tool handles, as structural posts in house construction, and for firewood. Charcoal obtained from this species is long lasting and has good weight. According to Romero Rangel et al. (2015), the saplings are edible, after being cooked, ground, and mixed with corn; they are also an ingredient in a potion administered to women after giving birth. The bark is used to alleviate inflamed gums, to tan leather, and in the preparation of agave-based beverages.

Amongst its numerous common names in Spanish, perhaps the most distinctive is encino chicharrón, based on the similarity between the leaves and the fried pork rinds popular in Mexican cuisine and known as chicharrones. The epithet crassifolia derives from the Latin crassus, meaning solid, thick, or coarse (it is the origin of the English word “crass”), + folia (“leaf”).