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Deciduous tree to 30 × 1 m dbh in the wild, anecdotally to 45 m (Hinkley 2014), making a narrow or rounded crown, often multi-stemmed from the base, and sometimes suckering from the roots. Bark grey-brown, flaking initially, rougher with age. Branchlets with lenticels, glabrous, rather stout. Buds pink-tinged to red.
Leaves rather fleshy in texture, often bronze on emergence, becoming dark green; opposite, 6–30 × 3.5–14.5 cm, elliptic to ovate, tapered to the base, apex acute and sometimes abruptly acuminate, margin entire. Upper leaf surface glabrous or sparsely hairy, undersurface usually hairy, especially on the major veins, with hairy domatia in the axils of major vein branches. Petiole 2–8 cm, sometimes hairy, pink-tinged to red. Stipules caducous, triangular, 6–10 mm, acute.
Inflorescence terminal on leafy shoots, in flat-topped, rounded or pyramidal racemes to 50 cm across in cultivation. Flowers white (perhaps yellow in some wild trees), heavily scented, 5-merous, about 2.5 cm across, on pedicels to 5 mm in summer. Calyx usually glabrous, the basal part around the ovary 3–4 mm, with 5 lobes, mostly 2 mm long and hairy. In a few flowers scattered through the inflorescence a single calyx lobe is greatly enlarged as a petaloid calycophyll to 8 × 6 cm on a 1–3 cm stipe, white at flowering time, persisting and taking on pink, red or purplish tones as fruit ripens. Corolla white, the tube to 23 mm long and densely hairy outside, with 5 rounded lobes, 5–7 mm. Stamens 5, inserted below the corolla throat, included.
Fruit a cylindrical or fusiform capsule to 1.5 cm, sweetly scented, red when ripe, the apical half splitting along the septa to release broadly winged seeds.
Habitat Deciduous forest in mountain valleys, 400-1600 (perhaps 2000) m., on various soil types , (Chen & Taylor 2011b, Zhang et al 2016)
USDA Hardiness Zone 6-10
RHS Hardiness Rating H6
Conservation status Not evaluated (NE)
For over a century, Emmenopterys henryi has been cultivated on the promise of the assertion by E. H. Wilson that it is ‘one of the most strikingly beautiful of Chinese trees’ (Wilson in Sargent 1917). The horticultural paradox is, however, that the tree is grown primarily for its spectacular, but fragrant flowers are rarely or never produced.
Discovered by Augustine Henry in the Three Gorges region in 1887 (O’Brien 2011) E. henryi was first introduced by Ernest Wilson in 1907 (W 622), from Hubei. This was the origin of Europe’s oldest trees. The tallest British specimens, one at Roath Park, Cardiff (17 m in 2018 – The Tree Register 2018), and two at Caerhays Castle, Cornwall, fall into this group. One of the original trees, planted at Kew in 1913 was micropropagated in the early 1980s when ailing (Upson 2013). This led to a very significant second distribution of Wilson material in Britain, including well-known specimens at Cambridge University Botanic Garden (Upson 2013) and Batsford Arboretum, Gloucestershire (pers. comm. M. Hall).
Later introductions include one from Yunnan by George Forrest in 1924 (F 25368) giving rise to specimens at RBG Edinburgh (Royal Botanic Garden Edinburgh 2018) and Borde Hill, Sussex (Harrison 2012). A collection from Anhui in 1988 (BLW 040) has been distributed in North America, initially by the US National Arboretum: significant trees at both the National Arboretum, Washington D.C. and the JC Raulston Arboretum, North Carolina share this origin. Another from Sichuan in 1996 (SICH 1847) can be seen at both Kew and Quarryhill Botanical Garden, California.
Despite the size of the oldest British specimens, none flowered until 1987 and since then an Emmenopterys flowering has remained a special event, often attracting media interest. The problem appears not be be one of age or size. Regular flowering from six years old in California (McNamara 2013) and ten years in North Carolina (pers. comm. M. Weathington) have been recorded. Climate seems to be the issue. At Villa Taranto, northern Italy, flowering has been regular since 1947, whilst at the Arboretum Kalmthout, Belgium, it has been frequent (though not annual) since 1987 (Rammeloo 2016). In Britain, the summer of 2018 was by far the best to date, including a first flowering of the century-old Cardiff tree. The Caerhays trees in more temperate Cornwall have yet to flower (2018). It seems clear that a hot summer, following a reasonably cold winter, stimulates flowering on the current year’s shoots.
Pollination studies are lacking, but field workers report diverse insects including bees and butterflies visiting flowering trees (for example Ma et al. 2012). The heavy scent, rumoured to be detectable at great distances, as well as colour act as attractants in this generalist strategy. The white calycophylls presumably add to the effect of the petals. While a yellow flowered variant could be horticulturally desirable, it is entirely possible that the mention of ‘white or yellow’ corolla in Flora of China relates only to discolouration during drying of herbarium specimens.
As well as their possible role in attracting pollinators, there has been speculation over a role for calycophylls in fruit dispersal, going back as far as the original description of the species (Oliver 1887). Against this. it should be noted that only a small proportion of fruits will have a calycophyll, and that it may well be normal for fruits to dehisce, releasing their winged seeds, while still on the tree. Without rigorous field studies, we just cannot know.
Emmenopterys henryi sometimes suckers from the root. In wild populations in Zehjiang, the degree of suckering varied between sites, and was correlated with the nature of the terrain, apparently contributing to survival where seed recruitment was poor (Ma et al. 2019). Suckering is horticulturally significant, affecting the overall appearance of a garden tree, as well as providing an easy means of casual propagation in the absence of seed production or the means to root tip cuttings. The trait seems unusual in the UK, not having been noted at Kew or Cambridge, and just occasionally at Batsford (pers. comm. A. Kirkham, P. Atkinson and M. Hall). However, it is quite easy to find reports of suckering specimens in the USA, notably a tree of about 10 m (2019) at the JC Raulston Arboretum, which suckers ‘quite prolifically’ (pers. comm. M. Weathington). Not surprisingly, root damage has been shown to encourage suckering (Guo et al. 2017), but this may not be the whole story. Suckering ability does not seem to be a characteristic of any one particular introduction. Rather, individual genotype is a more likely cause. Propagation from such a tree would result in suckering ability becoming locally common in cultivation, just as it would in the wild.
The conservation status of Emmenopterys has not been assessed by the IUCN, but in the literature it is widely considered to be threatened by habitat modification and loss. Wang et al. (2016) evaluated this species according to IUCN criteria and concluded it could be critically endangered (CR). The scattered distribution of the species suggests that existing populations may be relicts of a wider Chinese distribution in the past, fragmented by climate fluctuations in a heterogenous environment. On a smaller spatial scale and shorter timescale, this would mirror the situation in the genus as a whole. Analysis of patterns of genetic variation supports this (Zhang et al. 2016). There is considerable climatic variation across the range, giving hope that material able to flower in cooler summers may yet be out there. In the meantime, Emmenopterys henryi can be an attractive tree in leaf, especially when the bronzed young foliage is expanding.