Kindly sponsored by
John Grimshaw, Ross Bayton and Dan Crowley (2020)
Grimshaw, J., Bayton, R. and Crowley, D. (2020), 'Acer tonkinense' from the website Trees and Shrubs Online (treesandshrubsonline.
A deciduous tree to 12 m. Bark dark brown, smooth. Branchlets purplish-green to olive-brown, glabrous and waxy. Leaves subcoriaceous, broadly ovate in outline, 8–17 × 7–15 cm, palmately 3– to 5-lobed, lobes shallow, upper surface glabrous, lower surface glabrous but for the tufts of hair in the vein axils, margins entire or occasionally dentate (serrate in young leaves), apex acute; petiole 2–3.5 cm long, purplish-green; autumn colour orange-yellow to red. Inflorescence terminal, paniculate, 8–10 cm long, many flowered. Flowers 5-merous, usually dioecious; sepals triangular, purplish-green, petals yellowish, stamens 8, inserted inside the nectar disc, ovary pubescent. Samaras 1.8–3 cm long, yellowish, wings spreading horizontally. Flowering April to May, fruiting in September (China). (van Gelderen et al. 1994; Xu et al. 2008).
Distribution Myanmar China Guangxi, southern Guizhou, southeast Xi-zang, southeast Yunnan Thailand Vietnam
Habitat Mixed forest between 300 and 1800 m asl.
USDA Hardiness Zone 8-9
RHS Hardiness Rating H3
Conservation status Near threatened (NT)
Taxonomic note van Gelderen et al. (1994) recognised two subspecies with somewhat larger leaves: subsp. kwangsiense, with leaves 12–17 cm across with sparse teeth on the margin (cultivated by Plantentuin Esveld under glass in the Netherlands); and subsp. liquidambarifolium, with evenly lobed leaves 8–14 cm across. However, these subspecies are not accepted by Xu et al. (2008), whose more recent treatment is followed here.
Acer tonkinense is extremely rare in cultivation and was not seen in any collections visited in the course of research for New Trees. Grimshaw & Bayton (2009) summarised the little information that could be gleaned as suggestive that it is not hardy in most of our area and must be maintained under glass. It had, however, been offered commercially, most notably by Heronswood Nursery in their 2002 catalogue. The plants offered were grown from seed supplied by James Waddick of Kansas City, Missouri, obtained from Shanghai Botanic Garden, and were described as having thick leathery leaves, each of the five lobes terminating in a long-acuminate point. At Heronswood it proved ‘very hardy’ and formed a notable feature with ‘ashen lime’ stems in winter (Heronswood Nursery catalogue 2002). It comes into growth early in the year (D. Hinkley, pers. comm. 2007).
More recently, Dan Hinkley’s introduction of Acer fenzelianum (DJHV 06173), from Vietnam, has been erroneously circulated as A. tonkinense subsp. liquidambarifolium (listed in synonymy here). See the account of A. fenzelianum for more details of this collection. In Vietnam A. tonkinense appears to be restricted to limestone areas, such as in northern Ha Giang Province, and is absent from the Hoang Lien Mountain range, including Fan Xi Pan, from where numerous maple collections have recently been made. In that part of its range mature specimens are few and far between (pers. obs. 2017, 2018). As with many species its juvenile foliage can be markedly different from that of mature plants – its young leaves can be deep red to purple in colour, with this coloration persisting for some time on the lower surfaces.