Quercus hypoleucoides A.Camus

Quercus hypoleucoides is a standout, clearly of stellar horticultural quality, or as Cameron (2017) put it, ‘quite a star of the quercine scene’. But like some film stars, it is a bit of a recluse and continues to be rarer in cultivation than it should be. This is perhaps because it is, in Miller and Lamb’s (1985) words, ‘most unoak-like,’ with its upright branching habit and silver-backed foliage. Its stunning good looks would not be out of place among the beautiful oaks of Mexico, so perhaps what has drawn attention to this species is that it is found north of the US–Mexico border, among oaks that are in the norm more modest in appearance. A scarce and sporadic acorn supply may contribute to its low numbers in cultivation.

However, it is not as rare as it was, which is probably due in large part to US plant collector and nurseryman Sean Hogan raving about it and promoting it as a street tree. He is besotted by the dark green leaves, with shiny, leathery surfaces that contrast with the whitish undersides, ‘bright as a freeway reflector’ (‘cat’s eyes’ in an anglophone lexicon). Hogan’s first encounter with the species was as cultivated trees, grown from seed collected in Mexico, which he planted as street trees in front of his house in Portland, Oregon. He was so enamoured of them that he made a special trip in 1990 to the Chiricahua Mountains in Arizona to see them in the wild. It was in late December, with light snow on the ground, and the silver undersides lit up as if by floodlights by the reflection off the snow made a lasting impression (Hogan 2008). Back in Portland, though snow is scant, the slightest breeze causes the foliage to dance in the sunlight or the glow of a nearby streetlight. Hogan reports successful planting at low elevations in the US Southwest, though strangely the species does not seem to thrive when planted at higher elevation. It grows well on the US West Coast, but only began to enjoy popularity in the late 2000s. Trees planted in Seattle at the University of Washington Botanic Garden reached 15 m and are more open than those planted in drier places, and some branches have been broken by snow over the years (Hogan 2008). Though slow growing in the wild, it has grown moderately fast in gardens and as a street tree, withstanding drought in summer or winter and making a handsome 5–6 m in five years. Its strong roots help it withstand urban conditions, where summer irrigation accelerates growth. Cold hardiness will vary according to where it was sourced. Hogan’s trees, sourced mainly from southern Arizona and New Mexico, have survived −20°C or lower (Hogan 2008).

Quercus hypoleucoides also provoked gushing prose from le Hardÿ de Beaulieu & Lamant (2006). They describe shrubby clumps covering large areas, with an overall silvery hue, including the striking contrast between the dark green of the upper surface and the ghostly white of the undersides. The wind, which sways the branches though not the rigid leaves, reveals and accentuates this contrast. For them, it is one of the most beautiful oaks in the US, partly because it is so unlike the oaks that are found north of the Rio Grande. They lamented that this oak, ‘one of the most beautiful they have been allowed to observe’, was sadly almost impossible to find in cultivation, despite its evident ornamental merits. They attribute this to scarce acorn production during long periods of drought and the relative inaccessibility of wild populations. Hogan (2008) also comments on the difficulties of propagating from acorns, due to the stiff competition from blue jays and squirrels in the race for fresh seed. If acorns are obtained, germination is swift. He reports some success with cuttings, particularly with newly ripened suckered growth from the base, taken as heel cuttings in autumn.

It has been almost two decades since these authors decried the scarcity of Quercus hypoleucoides in cultivation, and while it is easier to come across, it is still far from common. The Tree Register only lists five specimens in the UK, three of them in Sir Harold Hillier Gardens. The champion for height and girth grows there, planted in 1973 and measuring 12 m × 38 cm (Heathcoat Amory 2009; The Tree Register 2025). Other small trees are listed at Wynkcoombe Hill in West Sussex and Cherry Tree Arboretum in Shropshire. Though there are other specimens in UK gardens that are not shown in The Tree Register (e.g. Chevithorne Barton in Devon, Thenford Arboretum in Northamptonshire, and Heanley Farm in Warwickshire – pers. obs. RC 2024), the species is poorly represented in UK collections and notably absent at Kew. Previous publications have been vague regarding a date of introduction to cultivation: Bean (1976) does not go further than venturing ‘of recent introduction,’ while le Hardÿ de Beaulieu & Lamant (2006) suggest that European introduction happened at some point during the final decade of the twentieth century. The 1973 introduction at Sir Harold Hillier Gardens is the earliest evidence we find of this species in cultivation.

In Europe the oldest specimen we have a record of is a tree at Arboretum des Pouyouleix, south-central France, grown from seed collected by Thierry Lamant in 2005 in New Mexico. Planted in 2007, the larger of two specimens had reached 9 m × 32 cm in 2021. It has proved remarkably cold hardy and did not suffer the slightest damage during a severe cold spell in February 2012 (temperatures at night of −18°C for fifteen consecutive days, with daytime temperatures never above −8°C). The ornamental potential of this species is evidently appreciated at this Arboretum, where nine trees were planted in alignment at the entrance in 2020 (B. Chassé, pers. comm. 2023).

At Arboretum de la Bergerette, southwest France, trees planted in 2009, from seed sourced in Arizona, already beguiled owner Shaun Haddock as young trees in 2012. He enthused about the narrow evergreen leaves with the occasional asymmetric lobe to add interest, the white undersides, and the purple new growth. They have grown vigorously there (Haddock 2012). Younger trees are growing in Iturraran in Spain and Arboretum Wespelaar in Belgium.

In the US it is found in arboreta in North Carolina (Bartlett Tree Research Laboratory and Arboretum in Charlotte and JC Raulston Arboretum in Raleigh) (pers. obs. RC 2024). It is more common in the west, most notably at Denver Botanic Gardens, withstanding Zone 6 conditions (Cameron 2017; Xera Plants Inc. 2025).

The species is remarkably absent in Australia, and in New Zealand where Bob Berry planted so many oaks from Mexico and the adjacent southwestern US. In Argentina, it is found at San Miguel Arboretum, where Sean Hogan’s long hand seems to have reached: the trees are grown from acorns collected from street trees in Portland in 2004. Two trees planted in 2005, multistemmed, have reached a height of 6.5 m with a 5 m crown spread; they have survived −12°C (P. Laharrague, pers. comm. 2024). Their foliage is quite dense, with particularly long leaves and striking clotted-cream-coloured undersides (pers. obs. RC 2026; and see images below). Young trees planted in Uruguay have shown vigorous growth in poor soil with minimal watering (pers. obs. RC 2025).

The species was apparently first encountered by botanists during the United States and Mexican Boundary Survey in 1848. It flummoxed taxonomists, presumably because it was so different to what had been found in the US before then. John Torrey (1859) suggested it might be Q. confertifolia, a Mexican species described by Bonpland and till recently considered synonymous with Q. mexicana. He also noted that Liebmann (1854) likely applied to specimens from this collection the name Q. cinerea Michx. (a synonym of Q. incana, an oak from the southeastern US). Engelmann was the first to describe it under a new name in 1876 as Q. hypoleuca. However, this very apt name (from ancient Greek ὑπο- (hupo-, ‘under’) + λευκός (leukós, ‘white’) had already been claimed by Miquel in 1858, for a plant later determined to be a Lithocarpus. The name had also been illegitimately used by De Candolle (1864), based on a herbarium label by Kotschy. Aimée Camus put things right in 1932 using the nomenclatural trick of adding -oides – from εἶδος (eîdos, ‘likeness’) – to the name, thus making it unique and legitimate while retaining the aptness of the epithet. Due to Draydon Jackson’s (1895) confusing practice of treating identifications as published names in Index Kewensis, Q. confertifolia Torr., a name Torrey never published, is often included in the synonymy of this species.