A deciduous tree to 20 m. Bark greyish-brown, smooth. Branchlets glabrous, purplish-red or greenish turning darker. Buds ovoid. Leaves chartaceous to often subcoriaceous to coriaceaous, broadly pentagonal in outline, base cordate to truncate, (3–) 5-lobed, 3.5–12 × 4.5–16.5 cm, lobes narrow to broadly ovate, apically acute or acuminate, margins crenate to serrate, upper surface mid-green, lower surface glossy green; petiole 3–7.5 cm long, red or green, glabrous, autumn colours yellow. Inflorescence, terminal, corymbose cymose. Flowers 5-merous, usually functionally dioecious, sepals hirsute, stamens 8, inserted inside the nectar disc, ovary hirsute. Samaras 1.8 to 2.5 cm long, wings spreading obtusely. Nutlets globose. Flowering April to May, fruiting in October (Xu et al. 2008).
Distribution Taiwan Central and Northern regions
Habitat Temperate forests between 1000 and 2000 m asl.
USDA Hardiness Zone 7-8
RHS Hardiness Rating H5
Conservation status Least concern (LC)
Taxonomic note van Gelderen et al. (1994) treat this as Acer oliverianum subsp. formosanum, though Xu et al. (2008) opt for treatment at specific rank, stating that it differs from A. oliverianum by having more flowers per inflorescence and different flavonoid patterns. Furthermore, Li (1952) states that A. serrulatum has crenate to serrate leaf margins (serrulate in A. oliverianum, which is somewhat ironic given the specific epithets involved), hirsute petals (glabrous in A. oliverianum) and shorter stamens. The leaves of A. serrulatum are also entirely glabrous, whereas axillary tufts are present on the lower surfaces of A. oliverianum leaves. The treatment of Xu et al. (2008) is followed here.
Acer serrulatum was reportedly first introduced by James Harris in 1980 (Harris 2000), though a tree recorded as this species at the John F. Kennedy Arboretum, County Wexford, Ireland apparently dates from 1973 (The Tree Register 2018), however the identity of this specimen has not been confirmed. It has been collected several times since the 1980s, with maturing trees commonly encountered in maple collections. One such introduction was made by Kirkham & Flanagan, who collected seed at 2210 m in Nantou County, Taiwan in 1992 (ETOT 64). Material from this source has been widely distributed and trees are generally doing very well, including one specimen at the Sir Harold Hillier Gardens, Hampshire that was 6.5 m tall in 2008 (The Tree Register 2018), and a flourishing grove at the University of British Columbia Botanical Garden in Vancouver (Flanagan & Kirkham 2005). Several introductions have been made by Bleddyn and Sue Wynn-Jones (for example, BSWJ 1891, BSWJ 6773, NMWJ 14521), while Dan Hinkley (for example, DJHT 99081, DJHT 99051) has also contributed to the material in collections.
Specimens often have a distinct elegance, with attractive dark olive-green foliage. The new growth emerges alarmingly early in the year and can be damaged even by light frosts, but usually recovers. The species has had something of a reputation for tenderness (van Gelderen et al. 1994), which may be accurate in parts of continental Europe, though plants appear quite happy at Arboretum Wespelaar, Belgium, albeit in a sheltered location. Any tenderness is certainly not borne out by experience in the United Kingdom or western North America, when trees have been carefully sited.
Morphologically, aside from a greater number of flowers per inflorescence, Acer serrulatum can be distinguished from A. oliverianum by the absence of axillary tufts of hair, which in that species are present. Interestingly, the bark of A. serrulatum can also appear slightly glaucescent, though this character is not necessarily consistent. Tom Christian (pers. comm. 2020) has observed that several young trees from NMWJ 14521 growing in a private collection in Berkshire, differ markedly in the strength of bark colouration. Dan Hinkley (Heronswood Nursery catalogue 2005) describes the trunk colour when mature as ‘a pleasing frosted light green’. Growth at the shoot tip continues all summer, the new leaves having a reddish or purple-bronze tinge that can persist on the undersides. In autumn it turns a good yellow, orange or red and holds its leaves late (L. Banks, pers. comm. 2006).