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A deciduous tree to 7 m. Bark greenish grey when young, turning darker with age. Branchlets glabrous, purplish red or greenish, turning darker. Buds, ovoid, with four pairs of scales. Leaves ovate in outline, base subcordate to rounded, three lobed, 6–15 × 5–21 cm, lobes broadly ovate, apically acute or acuminate, margins remotely entire, upper surface glossy green, lower surface paler, glabrous except for tufts in vein axils; petiole 2–4 cm long, red, glabrous. Inflorescence, terminal, corymbose, >10 flowered. Flowers 5-merous, usually dioecious, pedicels long and slender, sepals and petals oblong to ovate, sepals red, petals white, petals as long, or longer than sepals, stamens eight, inserted in the inside of the nectar disc. Samaras 4 to 6 cm long, wings spreading obtusely to nearly horizontally. Nutlets ovoid. Flowering April, fruiting in October (van Gelderen et al. 1994; Xu et al. 2008).
Distribution Myanmar China Southern Yunnan Thailand Vietnam
Habitat Moist forests, along water courses between 1200 and 2400 m.
USDA Hardiness Zone 9-10
RHS Hardiness Rating H2
Conservation status Vulnerable (VU)
This tender tree was introduced from Thailand to Sydney by the Australian botanist and horticulturist Peter Valder, and from there scions reached Firma C. Esveld in Boskoop, from which source material was distributed to other maple enthusiasts in Europe (J. Harris, pers. comm. 2006). The species survived for a decade at Esveld but was eventually killed by frost, and A. calcaratum was feared lost from cultivation (van Gelderen & van Gelderen 1999). Fortunately this is not the case, as it is grown by James Harris at Mallet Court Nursery, in a polytunnel, where it seeds freely and breeds true, enabling it to be made commercially available – and it is also now growing again at Esveld. Young plants are therefore occasional in cultivation, but require a warm, sheltered position to prosper. The evergreen leaves are rather elegant, and borne on green stems.