Acer henryi Pax

The sole Chinese representative of Section Negundo, Acer henryi was introduced to western cultivation from Hubei by Ernest Wilson in 1903, while collecting on behalf of the Veitch Nurseries (Bean 1976). The species had been discovered in 1888 by Augustine Henry, and described and named after him by Ferdinand Pax a year later (van Gelderen et al. 1994). Wilson made a second introduction in 1907 while working for the Arnold Arboretum (Sargent 1913) and the species was also encountered in the wild by numerous other western collectors active in China in the first half of the 20th century. Material was later reintroduced to the United States by the 1980 SABE expedition (Bartholomew et al. 1983), as well as via NACPEC expeditions in 2004 and 2008, the latter to Shaanxi and represented by plants at collections including the Morton Arboretum, the Dawes Arboretum and the Arnold Arboretum (American Public Gardens Association 2017).

Post-Wilson wild material in the UK includes plants grown from seed collected on the 1996 Sichuan expedition (SICH 1741) by Tony Kirkham, Mark Flanagan, Charles Howick and Bill McNamara. These collectors observed the species as a component of regenerating forest in association with Betula luminifera, Pterocarya hupehensis and Meliosma cuneifolia. Resulting plants grow in numerous collections including RBG Kew, Howick Arboretum, Westonbirt, and the Valley Gardens in Windsor Great Park, where it colours strongly in autumn. A spreading tree of vase-shaped form, the tallest example of Acer henryi in the UK is a tree of garden origin growing along The Link in Silk Wood at Westonbirt, measured at 11 m tall in 2024 (The Tree Register 2025). The largest in diameter is a tree at Caerhays Castle, Cornwall, which measured 57 cm dbh in 2016 (The Tree Register 2025). It was planted in 1934 having been acquired from Notcutts Nursery (The Tree Register 2025).

Most closely related to Acer cissifolium of Japan, A. henryi differs from that species in its narrower inflorescences that are held outwards, rather than being pendulous as in A. cissifolium. A. henryi leaves tend to be a darker green than those of A. cissifolium, turning deeper shades in autumn. Though leaves of both species can be toothed, those of A. cissifolium are often more prominently so, and virtually entire-leaved specimens of A. henryi can be found. The two species are also often separated by the colour of their second to third-year shoots: those of A. henryi remain green, whereas in A. cissifolium they are matt brown, however, some recently introduced material appears to defy this character (e.g. BCJMMT 68 at Arboretum Wespelaar) and it is advisable to examine multiple characters before settling on a determination. Furthermore, among garden origin plants, possible hybrids between the two should certainly not be discounted.

In cultivation Acer henryi can be assumed to favour the same general conditions as A. cissifolium, perhaps including a tolerance for alkaline soils that seems to be widespread throughout this section of the genus. It is rare in North America, where Michael Dirr has observed that A. henryi is more cold tolerant than A. cissifolium, surviving temperatures as low as –30°C, which might make it a better choice in colder areas of the midwest and northeast, although the only sizeable example he cites is a specimen 10.6 m tall in Atlanta Botanic Garden in 2006 (Dirr 2009). Jacobson has observed that autumn colour in North America ‘varies from a good red…to simply dreadful’ (Jacobson 1996).