Tree to 20 m. Bark grey-brown, soon fissured and flaking. Twigs grey-brown with silky hairs at first (the hairs never glandular), becoming glabrous and purplish. Leaf 3–10 × 2–4 cm, elliptic to narrowly oblong; margin irregularly and sharply double-toothed, the teeth sometimes mucronate; lateral veins in 13–16 quite closely parallel pairs; petiole 3–5 mm long, with dense non-glandular hairs. Fruiting catkin 2–3 cm long, with a densely pubescent peduncle; bladders long and narrow (20–26 × 6–8 mm), their bases constricted into a stipe, their tips rounded and with a short whisker. Nutlet large (7–10 mm long), shiny red-brown, glabrous. (Li & Skvortsov 1999).
Distribution China Zhejiang (Tianmu Shan)
Habitat Subtropical mountain forests.
USDA Hardiness Zone 5
RHS Hardiness Rating H6
Conservation status Critically endangered (CR)
Distinct in its slender, stalked fruit-bladders, Ostrya rehderiana is one of the world’s rarest trees: it is endemic to the western side Tianmu mountain in north-western Zhejiang where only five old trees remain following extensive forest clearance (Shaw et al. 2014). A nature reserve was designated in 1956 to protect the remaining population, which is now successfully regenerating (Lundquist 2018) but shows limited genetic diversity.
Ostrya rehderiana was introduced to the United States by Heritage Seedlings of Oregon in 1992, one earlier introduction to the Arnold Arboretum in Massachusetts having failed (de Jong 2019). Although the forests where the species survives in the wild are subtropical (Li & Skvortsov 1999) Tianmu sustains populations of many species that are far hardier than the location would suggest. The mountain – at least those parts that have for centuries enjoyed the protection afforded by the proximity of temples – is perhaps best known as one of the very few refuges of (probably) wild Ginkgo biloba; the forests also support populations of towering Pseudolarix amabilis and a bewildering diversity of broadleaves including such choice trees as Liquidambar acalycina (T. Christian pers. comm. 2022). Ostrya rehderiana is proving equally hardy and as easy to cultivate as any of its cousins; twelve were established at the Arnold Arboretum in 2002, from which plants were sent on to Von Gimborn Arboretum in the Netherlands in 2008 (de Jong 2019) and to the Scott Arboretum in Pennsylvania (Stewart 2010). These last two accessions are both thriving and growing into shapely trees, with the elegant, many-veined leaves typical of their genus.