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Tree to 20 m (?). Branchlets yellowish green and sparsely pubescent. Leaves deciduous, 4–8 × 2.5–5 cm, ovate or elliptic, both surfaces glabrous or with minimal pubescence, seven to nine lateral veins on each side of the midvein, margins with minute serrations towards the apex, apex obtuse or acute; petiole with pubescence limited to the upper furrow, 1–1.6 cm long. Staminate inflorescences catkin-like, 3–8 cm long; pistillate inflorescences subsessile, 5–13 in a panicle, ellipsoid, 1.3–1.5 cm long. Cone woody, 1.2–1.5 × 0.6–0.8 cm, bracts 0.4 cm wide. Flowering in autumn (Taiwan). Li & Skvortsov 1999. Distribution TAIWAN. Habitat This is a pioneer species and can be found in a variety of habitats and elevations. USDA Hardiness Zone 8. Conservation status Not evaluated. Illustration NT139. Taxonomic note Alnus henryi is poorly known and may be conspecific with A. formosana. The only major difference between the two appears to be one of phenology: A. formosana flowers in spring while A. henryi flowers in autumn.
Neither Flora of China nor any other authority is able to provide a mature height for Alnus henryi, but it can be expected to achieve much the same stature as A. formosana. Seed was collected from 5 m trees at 200 m in Taichung Co. by Kirkham and Flanagan during their 1992 expedition to Taiwan (ETOT 40), and their field notes describe it as an abundant pioneer, and ‘a common and successful tree’ – but it would seem that it has a limited distribution on the island. They also note that it grows on ‘south-west facing slopes in full sun’, suggesting that a warm site is needed in cultivation. This collection established the species in cultivation, but it is rare. There are several trees at Wakehurst Place; the champion, however, is a 9 m (15 cm dbh) specimen at Sandling Park, Kent, described by Owen Johnson (2007) as a ‘tree of great grace’.