Tetracentron sinense Oliv.

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Credits

Sven Bronckaers & Richard Moore (2024)

Recommended citation
Bronckaers, S. & Moore, R. (2024), 'Tetracentron sinense' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/tetracentron/tetracentron-sinense/). Accessed 2024-05-26.

Common Names

  • Spur-leaf
  • 水青树 (shui qing shu)

Synonyms

  • Tetracentron sinense var. himalense H.Hara & Kanai

Other taxa in genus

    Glossary

    acuminate
    Narrowing gradually to a point.
    herbarium
    A collection of preserved plant specimens; also the building in which such specimens are housed.
    pioneer species
    Early colonists of disturbed areas.
    variety
    (var.) Taxonomic rank (varietas) grouping variants of a species with relatively minor differentiation in a few characters but occurring as recognisable populations. Often loosely used for rare minor variants more usefully ranked as forms.

    Credits

    Sven Bronckaers & Richard Moore (2024)

    Recommended citation
    Bronckaers, S. & Moore, R. (2024), 'Tetracentron sinense' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/tetracentron/tetracentron-sinense/). Accessed 2024-05-26.

    Deciduous tree, 20–30(–40) m tall, 1–1.5 m dbh, crown broad-conical, mature bark grey-brown, plated. Glabrous in all parts. Branchlets grey-brown producing leaves borne singly on alternate, short spur shoots bearing conspicuous concentric scars from previous season’s growth. Buds narrow, 1 cm long; stipulate. Petioles slender, 2–4 cm long, semi-terete, canaliculate. Leaves chartaceous, dark green, abaxial surface distinctly pale, broadly to narrowly ovate, base deeply to shallowly cordate, apex acuminate, margins sharply serrulate; palmately veined (5–7) from base, impressed on upper surface, strongly raised beneath. Inflorescence green, slender, pendulous, 7–20 cm long, axillary at the base of the petiole or terminally from spur shoots, bearing c. 80–125 individual flowers. Flowers apetalous, yellow-green, hermaprodite, whorled around peduncle, sessile. Sepals 4, broadly deltoid, 0.3–0.5 mm long, apex rounded. Stamens 4, antesepalous, filments 1.5–3 mm long, subterete; anthers, yellow-green, 0.4–0.8 mm long, longitudinally dehiscent. Styles 4, slender, initially erect before becoming recurved at anthesis, stigma along ventral surface of style. Fruit 4-locular, dehiscent follicles, 2.5–5 mm, maturing to brown, dehiscent upon drying. Seeds up to 6 per follicle, spindle-shaped 2–3.5 mm, narrowly winged at either end. Flowering: April–July; fruiting: July–November (in situ). Chromosome number: 2n = 48. (Oliver 1889; Smith 1945; Dezhi & Bartholomew 2001).

    Distribution  BhutanMyanmar (North) China (Gansu, Guangxi, Guizhou, Henan, Hubei, Hunan, Shaanxi, Sichuan, Xizang, Yunnan) India (Northeast) Nepal (East) Vietnam (North)

    Habitat On steep mountain slopes, scree slopes, narrow valleys and stream banks, amongst mixed evergreen and deciduous forests, 1100–3500 m asl.

    USDA Hardiness Zone 6-7

    RHS Hardiness Rating H6

    Conservation status Least concern (LC)

    Taxonomic note A variety, Tetracentron sinense var. himalense H.Hara & Kanai is still often encountered in literature and nursery catalogues, but we follow most modern treatments in considering this synonymous with the species; see below for further discussion.

    This remarkable tree was discovered for science by Augustine Henry in Hubei, China in the mid-1880s and later described by botanist Daniel Oliver in 1889 (Oliver 1889). It was later brought into cultivation in 1901 by Ernest Wilson who collected it on his first expedition to China for the Veitch Nurseries, who had contracted him to collect seed of horticultural interest, most particularly the Dove Tree, Davidia involucrata. Wilson was instructed to visit Augustine Henry who was working in Yunnan at that time, to verify the best places to look for Davidia seeds. It was close to the village of Yin Kou where he found a fine tree of Davidia almost 15 m in height alongside specimens of Pterocarya macroptera var. insignis and Tetracentron sinense from which he collected the first seeds to be sent back to the UK (under collection number W 2156) (Sargent 1913; Briggs 1993). A 1905 accession of Tetracentron sinense, from the very same batch of seed (W 2156) growing at the Royal Botanic Garden Edinburgh (RBGE 2024) is one of the oldest surviving original collections of this species in UK and is the UK & Ireland champion tree for girth; however, this specimen is now showing its age with a large wound up one side of the trunk and it seems to be in terminal decline, its old age and various other ailments exacerbated by honey fungus. Fortunately somebody saw fit to propagate it, and a cutting-raised plant now grows at Dawyck Botanic Garden in the Scottish Borders. This may also be the source of a tree at Crathes Castle, Aberdeenshire, UK.

    On later expeditions Wilson collected Tetracentron again several times, including in 1910 (W 4328) when he was collecting for the Arnold Arboretum, but despite having been in cultivation for well over a century it remains a rare tree in gardens, largely confined to specialist collections throughout our area. The public-facing database of The Tree Register of Britain and Ireland lists only twenty two notable examples, while the Beltrees database of notable trees in Belgium lists only four (Tree Register 2024; Arboretum Wespelaar 2024), though plants of wild origin have been readily available from British nurseries in recent years. In his North American Landscape Trees the Seattle-based dendrologist Arthur Lee Jacobson (1996) calls it ‘extremely rare’ , but it has long been championed as a tree for the Pacific Northwest by Daniel Hinkley, who grows it very successfully in his garden at Windcliff, Indianola, Washington, and has collected it on several occasions in Vietnam; at the University of British Columbia Botanical Garden are several specimens of Chinese origins grown from collections made the late Peter Wharton. Conversely, in early 2024 the Arnold Arboretum’s Plant Search tool confirms there are no extant trees at that insitution, further evidence that it is probably ill suited to a truly continental climate (Arnold Arboretum 2024).

    For a long time botanists believed the range of the species had its western limit in northern Myanmar; however, in 1963 during a Japanese expedition to eastern Nepal, a new population was discovered, originally described as the variety Tetracentron sinense var. himalense H.Hara & Kanai based upon its larger leaves, with a longer and finer acuminate tip and with laxer fruiting catkins (Hara & Kanai 1964). This variety is no longer recognised and is considered synonymous to the species based on morphological variation across its range within which the features used to distinguish this variety do not justify it being separated at varietal rank. Comparing herbarium specimens at Kew shows there is not that much variation between the collections of different provenances. Only leaf size and width varies somewhat, where the plants originating from Yunnan had the broadest leaves and those from Gongga Shan in Sichuan the narrowest (Rix & Crane 2007). Not long after being discovered in Nepal, as predicted by Hara et al., plants were also found in Bhutan and Assam in 1967 (Srinivasan & Sen Gupta 1966; Hara 1967), therefore showing that Tetracentron has a continous range from eastern Nepal through to eastern Hubei Province in China.

    ​In the wild Tetracentron sinense is typically found on steep mountain slopes, scree slopes, in narrow valleys and often near stream banks amongst mixed evergreen and deciduous forests upto altitudes of between 1100–3500 m. Trees are often branching from low down with a broad, roughly conical shaped crown. Associated species include: Alnus nepalensis, Davidia involucrata, Euptelea pleiosperma, Cercidiphyllum japonicum var. sinense, Emmenopterys henryi, Cornus chinensis, Pterocarya macroptera var. insignis, Schima villosa, Castanopsis wattii, Lithocarpus chintungensis, Tsuga dumosa and Taxus wallichiana var. mairei (Sargeant 1913; Wilson 1913; Tang et al. 2013). Tetracentron sinense is classed as a pioneer species and is very fast growing with cultivated specimens reaching 5 m in height after only 10 years from seed, planted in a moist woodland in North Devon (Rix & Crane 2007). As such and due to its wood structure Tetracentron produces weak timber and is not widely harvested for its wood, nor is it a suitable building material; although in China it has been harvested to quite some extent for furniture, ornaments and in medicine negatively impacting wild populations (Chen et al. 2023). Ernest Wilson writes a rather amusing acount of his experience climbing up a specimen of Tetracentron in Hubei Province, China in order to photograph the upper branches of a neighbouring Davidia ‘By climbing a large Tetracentron tree growing on the edge of a cliff, and chopping off some branches to make a clear space, I manage to take some snapshots of the upper part of the Davidia tree in full flower. A difficult task and highly dangerous. Three of us climb the tree to different heights and haul up axe and camera from one to another by means of a rope. The wood of Tetracentron is brittle, and the knowledge of this does not add to one’s peace of mind when sitting astride a branch about 4 inches thick with a sheer drop of a couple of hundred feet beneath.’ (Wilson 1913). It reproduces by the dispersal of very small, wind dispersed seeds, released in late autumn and in the wild it has been documented that the respouting of specimens damaged by landslides also supports the stability of populations. Despite the rather unstable habitats in which T. sinense is found it has been shown that these conditions are of benefit to its survival providing an ecological niche whereby competition from other species is limited by such conditions and where T. sinense excels due to its capability as a fast growing pioneer species (Tang et al. 2013).

    With reliable summer heat Tetracentron sinense can be a striking tree in flower, when a profusion of catkins draw the eye from a great distance, but in cooler summer areas flowering is more sporadic. Still it makes for an attractive tree in cultivation and is most highly regarded for its handsome foliage, which can turn lovely shades of yellow and orange in autumn, but caution is advised, for the quality of the autumn colour is variable, with some cultivated specimens providing a rather disappointing spectacle (Hinkley 2019; RM pers. obs.). As trees mature they also develop a fine plated camouflage-like bark, predominantly grey-brown in colour, which provides winter interest as do the dried catkin-like infructescences, hanging elegantly from the branches. The winter buds are also unusual, somewhat resembling pigeon claws. It is certainly a curious species that attracts attention due to its unusual characteristics, and its cultivation is more than warranted if only for its fascinating evolutionary history and as the only member of this unusual genus.

    Tetracentron sinense is fully hardy down to temperatures of –15 to –20°C and tolerates a range of different soil conditions from acid to chalky, alkaline soils, but it performs best in areas where the soil moisture levels don’t drop too low during the summer. Trees are best positioned in light-shade but are tolerant of full-sun (Rix & Crane 2007; Missouri Botanical Garden 2022). As mentioned it is fast growing and as such may require some formative pruning during its early development; however, this species develops naturally into an attractive shape, broad and bushy when young becoming more upright and broadly conical with age.

    Propagation of this species is most easily achieved by seed (RM pers. obs.). Fresh seed germinates easily and quickly, surface sowing onto a moistened, fine, multi-purpose compost with a light covering of vermiculite to ensure the seed doesn’t dry out. Seed should germinate within six to eight weeks of sowing, often sooner. Seed pots are best kept within a closed unheated propagator or within sealed bags to retain moisture levels until germinated seedlings are ready to be pricked out and potted on. It is essential that the environmental conditions are adjusted slowly to ensure the seedlings do not get shocked when moved out to an environment of lower humidty. From cuttings Tetracentron sinense is known to be somewhat difficult, however, cuttings are best taken from semi-ripe growth in mid-late summer from good vigorous shoots, if sprouts from near the base of the stem are available they make ideal cutting material. Cuttings should ideally be between 10–15 cm long with the soft tip and lower leaves removed to reduce water loss, leaving two leaves at the top of the stem which can be cut in half if too large. Cuttings should then be inserted into a lightly moistened compost and kept within a closed propagator or mist unit to retain a high humidity, ideally on a heated bench (RM pers. obs.).