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Tree to 23 m tall. Bark pale brownish grey, developing close vertical ridges in maturity. Twigs slender (1.4–2.5 mm thick), green, usually glabrous. Buds 6–7 mm long, with three scales visible, the lowest swollen and over half the length of the bud; usually green and shining. Leaves 8–13 × 5–9 cm, broadly to narrowly ovate, very oblique at the base and often with a bulge in the lobe on the big side; margins entire, or with distant rod-like teeth, or very shallowly serrate; upper surface dark green and often notably matt, lower surface green to white with a variable stellate tomentum (most hairs with 8 arms). Floral bracts usually large (9–16 × 1.4–2.5 cm), pale green, with variably dense white stellate tomentum on the lower side. Inflorescence drooping, usually branched 3 times with 10–15 flowers in a tight cyme; flowers small (6–9 mm across), beaker-shaped. Staminodes present. Fruits c.10 mm, spheroid, unribbed, uniformly mamillate, covered in a dense, pale brown stellate tomentum; wall 0.8–1.3 mm thick, woody and hard to break (Pigott 2012, Flora of China 2018).
Distribution China Guangxi, Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Sichuan, Yunnan, Zhejiang
Habitat Mountain forests
USDA Hardiness Zone 6b-9
RHS Hardiness Rating H5
Tilia tuan, in Donald Pigott’s very broad interpretation of the species (Pigott 2012), is the most widespread Chinese lime (the only one that extends into the subtropics of North Vietnam), and the most variable member of the entire genus. Trees which grow in the warm-temperate and largely evergreen forests of the south-east tend to conform – while remaining deciduous - to the leaf-shape which is characteristic of many species in these habitats and helps to shed abundant summer rainfall: narrowly ovate (up to three times as long as broad), untoothed, and with a long ‘drip-tip’. Other forms have the more heart-shaped, serrated leaf which is characteristic of Tilia, while the majority of trees have leaves almost twice as long as broad (and still the narrowest of the genus), with a few marginal ‘teeth’ which are really just the emergent tips of the main veins (and which are always much shorter than the similar structures in T. henryana). There is often a distinctive wave in the margin of the larger lobe at the leaf’s base. The underside of the leaf also shows the genus’ whole gamut, from green and almost hairless to densely silver-felted. Pigott (2012) conserves two subspecies from south-east China: subsp. tristis, with large ovate leaves whose high number of parallel main veins (9–11) make them look particularly unlike a lime’s, and subsp. oblongifolia, whose narrow leaves are entire and whose veins curve away from the margin and link to the next vein up, dogwood-fashion.
Very few of these exquisite and delightfully idiosyncratic variants are cultivated in the west; most are probably tender, though a tree from Hebei [HUBEI?] survived for some years in the Arnold Arboretum in Massachusetts (zone 6b) (Pigott 2012). Many local populations are likely to be threatened by forest clearance. Ernest Wilson introduced at least two hardier variants while collecting for Veitch at the start of the 20th century (along with W 4410, originally identified as T. oliveri but considered to be T. tuan by Keith Rushforth who has taken grafts from a tree which used to grow in the Dawyck Botanic Garden, a cold place). Beautiful trees presumably from Wilson’s seeds grow in the lime avenue at Thorp Perrow, Yorkshire (planted in 1936 and 21.5 m × 60 cm dbh in 2014) and in the Royal Botanic Garden Edinburgh (accessioned in 1913 and 10 m × 37 cm dbh in 2014) (Tree Register 2018). Many English gardeners’ introduction to the species will have been the tree planted in 1933 in Stephanie’s Glade on the Borde Hill estate in West Sussex, which had been obtained for the sale of Vicary Gibbs’ collection at Aldenham in Hertfordshire as ‘var. chinensis’ (which it is not) and which has grown into a lime of unrivalled elegance, 16 m × 46 cm dbh in 2015 (Tree Register 2018); sadly this part of Borde Hill is no longer accessible to the visiting public. A variant with finely serrated leaves exquisitely grey-felted underneath and with only 3–6 flowers in each inflorescence was introduced from the Jizu Shan in Yunnan in 1993 by Donald Pigott as ‘var. chenmoui’, though Pigott no longer believes that the form merits varietal status (Pigott 2012). Seedlings from this collection have thrived across Britain, reaching 10 m × 24 cm dbh at the Cambridge University Botanic Garden by 2014 and 12 m × 21 cm dbh in the National Collection at Peasmarsh Place in East Sussex by 2018 (Tree Register 2018); each leaf is so perfect that it looks as if it belongs in a museum case. Another form with serrated leaves but with 16–22 flowers per inflorescence (the true ‘var. chinensis’) is labelled as a young tree at the Bluebell Arboretum in Derbyshire, but it is possible that many/most plants grown as this variety in the UK are actually scions of the typical tree from Borde Hill.