Toona sinensis (A. Juss.). M. Roem.

With its handsome pinnate leaves and potentially large stature Toona sinensis, Chinese Toon, is an important horticultural subject as well as being a source of timber. It is a fast-growing, readily cultivated tree for most soils in temperate regions (and at altitude in the tropics), making an excellent, generally disease-free street tree, affording good shade in hot streets in summer. Conversely, and perhaps uniquely for a tropical timber tree, its seedlings are also grown as ‘baby leaf veg’, germinated and harvested like other ‘microgreens’ – for example under the name ‘beef-and-onion plant’ by Suttons Seeds.

These two extremes of usage coincide in traditional Chinese cultivation, where it is valued for its timber, and its medicinal and edible qualities. The timber is reddish, fragrant and easily worked, so has been used for furniture and construction, including for bridges in China. According to Wang (1988) Chinese toon has been grown for its wood since before the middle of the third century BCE. The bark is astringent and purifying, the powdered root diuretic. The young shoots and leaves are crisp, and distinctly aromatic, with a floral, onion-like aroma when fresh, also found in the seedlings. The leaves are a good source of antioxidants and contain beta-carotene, vitamin E, riboflavin, folic acid, calcium and iron. For over 2000 years they have been boiled and eaten as a vegetable by the Chinese in China – and subsequently Malaysia and beyond, for their umami flavour, with both earthy and pungent flavours reminiscent of a blend of garlic, mustard greens and fermented chives. Today the salted shoots are usually eaten cold, with sesame oil (Valder 1999). Commercial pastes prepared in China are exported all over the world and are eaten with rice porridge and, particularly, in egg and other named toon dishes with fried rice, noodles, bean curd or mushroom soup (Yong Yang, pers. comm. 2021).

Formerly ‘very common’ around Beijing, and in western and central China generally, Chinese Toon has been much cultivated in central China, where the trees were often recorded as disfigured because they were kept dwarf, so that young shoots could be more readily harvested (Henry 1907 in Elwes & Henry 1906–1913, Rehder & Wilson in Sargent 1916). Chinese Toon was sometimes grown thus in peach orchards, for example (Koller 1978), but it was also valued for its wood, which was used in making furniture and window frames at the beginning of the last century, then being one of the most appreciated of all Chinese timbers (Yong Yang, pers. comms. 2021). Almost 80 years ago, French botanist Auguste Chevalier (1944) was promoting use of Chinese Toon in temperate-zone plantations. Hitherto, though, its fine wood has not been appreciated as much as that of related species but, with the diminution of available timber supplies of those, it could well come to be of great significance, bearing in mind its easy cultivation – provided root suckering can be minimised. In warm countries it can become invasive, however. Modern usages for the wood include the manufacture of boxes, barrels, crates and pallets, while it already has a place in joinery, and the making of fences and gates, flooring and panelling, besides the production of short-fibre pulp. It is also of value in the woodware industry, being used for cutlery and tool-handles, besides musical instruments, including guitars, and marquetry, as well as in wood carving and turnery.

In Chinese literature, Toona sinensis figures in classical metaphor, with a mature tree representing a father. This imagery persists even today, if rarely, in extending best wishes (椿萱并茂) in a letter to a correspondent’s parents, “hoping that your Toona sinensis and daylily (Hemerocallis) live long and healthily”, with Toona sinensis referring to the father and daylily to the mother (Yong Yang, pers. comm. 2021). Moreover, Chinese Toon was often planted in the yard of a house (see (Valder 2002: 156–157), symbolising father, with daylily in the ‘northern room’, symbolising mother.

In the nineteenth century, Chinese Toon was described independently in France (1830, from material collected in China in 1743), then Britain (1839, from India) and, lastly, The Netherlands (1861, from Indonesia), so receiving three binomials now considered synonyms. The first named was due, ultimately, to the work of Pierre Nicolas Le Chéron d’Incarville (1706 – 1757), who was a French Jesuit missionary sent to China in 1740; he died there. A pupil of Bernard de Jussieu (1699–1776) at the Jardin du Roi in Paris (now Jardin des Plantes), Incarville sent to Jussieu, by Russian caravan, 149 herbarium specimens, as well as seeds, of different native plants from the Beijing area. The specimens included a herbaceous plant which was to be named Incarvillea sinensis (Bignoniaceae), commemorating him, and the Tree of Heaven, Ailanthus altissima (Simaroubaceae), which Incarville called ‘frêne puant’ (stinking ash), besides Toona sinensis (his ‘frêne odorant’).

Contrary to what is to be found in much secondary literature, Incarville’s collections did not effect the introduction of Chinese Toon to European cultivation. However, his seeds of the Tree of Heaven led to that tree becoming established in Jussieu’s garden and, around 1751, at the Chelsea Physic Garden, London (Bretschneider 1898) – with the eventual, well-known, dire consequences across Europe and the western hemisphere, as well as Australia. Among many other Chinese tree species, Incarville also introduced Styphnolobium japonicum, Koelreuteria paniculata and Platycladus orientalis. After Bernard de Jussieu’s death, Incarville’s collections passed to his nephew, Antoine Laurent de Jussieu (who described the Chinese Toon as Cedrela sinensis – see above) and are preserved in the herbarium of the Muséum national d’Histoire naturelle in the Jardin des Plantes in Paris. In 1839, the eccentric and prolific Italian-American botanist, Constantine Rafinesque proposed (in a book on mulberries!) that Incarville’s ‘frêne odorant’ might be called Mioptrila odorata and, had he been less hesitant in his text, Mioptrila would have been the correct name for what is now Toona, a name published a few years later; long before all that, the great orientalist, Sir William Jones, had Latinised a local Indian name, Cuveraca, for Toona ciliata, in 1795, though, again, it was used in an unacceptable nomenclatural way.

Chinese Toon was introduced to Sri Lanka in 1852, but the source is obscure, though likely Indonesia, as Macmillan (1935) used the name Cedrela serrulata (see above) with the vernacular name, Java Mahogany. It continues to be much planted on tea estates there for shade, and for windbreaks, besides for its timber (Mabberley 1995); it has become naturalised in disturbed vegetation in the lower montane forest of the island. Introduction to cultivation in Europe until 1861 or 1862, when, through the good offices of the French minister in Beijing, the diplomat, writer and plant collector (Gabriel) Eugène Simon (1829–1896) sent material (according to some sources as a live plant, though likely just seeds) to Paris. After working in Senegal, Simon had been sent to China and Japan in 1860 to study local agronomic practices. That November, during the Taiping Rebellion, just a few weeks after the end of the Second Opium War and the sacking of the Summer Palace by the French and British, Simon was appointed French Consul in what is now Ningbo, south of Shanghai; he left China at the end of 1871 and was later appointed French Consul in Sydney. From China he sent live plants, as well as seeds and herbarium specimens, of Chinese plants to the Jardin des Plantes (Bretschneider 1898). However, it should be noted that, according to Baltet (1895), the Jardin also received seeds from Father Armand David CM (1826–1900) as early as 1862.

It appears that Simon had connections with the great nursery firm of Thibaut & Keteleer of Sceaux, near Paris, which likely received seeds from Simon himself, because the nursery was soon offering Chinese Toon for sale. It was rapidly spread in the French trade, being rapidly listed by leading provincial nurserymen like Lery at Angers, Dauvesse at Orléans and Simon-Louis at Metz-Plantières, for example. In 1865 a Chinese Toon, raised in the nursery of the Jardin des Plantes and planted out on the bank of the Bièvre between rue Buffon and rue Poliveau, was duly named Ailanthus flavescens Carrière, though it is easily distinguished from true Ailanthus by the absence of glandular teeth on the leaflet margins (marked in an old name for A. altissima, A. glandulosa), besides the shoots with very different odours.

By 1875, the original tree, then with a bole 20 cm in diameter 1 m above the ground, flowered for the first time, thus revealing its true identity. Élie-Abel Carrière (1818–1896) redeemed his earlier mistake by pronouncing the living material identical with authentic herbarium material of ‘Cedrela sinensis’; a flowering branch was exhibited at a meeting of the Académie des Sciences in Paris the next year (Decaisne 1876). By 1891 the tree had attained ‘40 feet’, and when Henry Elwes saw it there in 1905 it had a girth of ‘4 feet’ (Henry, 1907). It died in 1970, but, according to the record of historical trees at the Jardin des Plantes, there is today on the site of the old nursery, a tree which grew from one of its root suckers (Frédéric Achille, pers. comm. 2021).

By 1883 Chinese Toon started to become one of the characteristic street trees of parts of Paris (as it is today), because Charles Rafarin (?1826–1887) of the city’s horticulture department, charged with managing street trees in the face of the disease-proneness and deaths of Ailanthus altissima widely used in the boulevards, decided to trial Toona sinensis that year. The first Toona to be planted out, in 1886, were in rue du Jourdain, Belleville in the XX^e arrondissement (André 1891, Pinelle 1922); although pruned heavily in 1920, the trunks of those original trees had a circumference of 1.2 m by 1922. By 1891, though (André 1891), there had been no successful seed set from flowering trees in Paris, so the early plantings must all have been clonal.

In 1922 there were 2452 Chinese Toons in Paris streets, particularly fine being those in the avenue des Gobelins, boulevard de l’Hôpital, boulevard de la Bastille, boulevard Richard-Lenoir and avenue Parmentier (in some of which they are still the principal street-trees). Toona sinensis indeed proved to be less prone to disease and insect-attack than Ailanthus altissima, but, perversely, today, many of the avenues of Chinese toon have the odd Ailanthus amongst them, no doubt muddled as young plants in a nursery. But it is difficult to understand how herbarium specimens of flowering material of Chinese Toon from Yunnan also came to be assigned to Ailanthus (yet again), when François Gagnepain (1866–1952), working in the Muséum in 1944 referred them to his ‘new’ species, A. mairei Gagnep. – particularly when the label written by the eponymous French missionary collector, Édouard-Ernest Maire (1848–1932, also commemorated in Chinese Yew, Taxus mairei) explicitly notes (my emphasis) ‘arbre moyen dont les jeunes pousses sont comestibles’!

Since then, some of the Chinese Toons in Paris have been replaced (Henri Peyrétout pers. comm. November 2021) with Gymnocladus dioica (Leguminosae) and Fraxinus spp. (Oleaceae). Meanwhile, Toona sinensis has become quite a common tree in Belgium and The Netherlands, though it seems not to have been widely introduced in the United States until after this early spread in Europe.

According to Garden and Forest 9: 279 (1896) a tree planted in West Virginia about 1888 was ‘20 feet’ tall in 1896. Suggestive of even earlier plantings, a tree flowered in both 1895 and 1896 at Thomas Meehan’s nursery, Germantown, Pennsylvania (Garden and Forest 9: 260. 1896), by which time Samuel Moon of Morrisville, Pennsylvania, was offering plants of ‘Ailantus flavescens’ at $1.50 (Catalogue of Ornamental trees (etc.) p. 4. 1896). Meehan’s was the source of plants used in street plantings (mostly now removed) in Philadelphia, where the oniony odour they imparted to the air was unmistakeable (Tony Aiello, pers. comm. Sept. 2021). Despite this perceived downside Koller (1978) has made a powerful case for reviving ornamental plantings of Chinese Toon in US urban landscapes.

Chinese Toon was grown from seed at the Arnold Arboretum, Massachusetts, in 1892 ([Wilson] 1926), though the oldest plant there today came from the nursery of Jacobus Jurissen en Zoon in Naarden, Netherlands, in 1903; in 2002, its trunk snapped in half and was removed, though it resprouted such that a new trunk is now about 10 m tall and has a 17 cm diameter bole (Michael Dosmann, pers. comm. September 2021).

Chinese toon is propagated by seeds (though damping-off can be a problem) or by stem (see Koller (1978) for protocols) or root cuttings. It is tolerant of most soils, including heavy clay and very limey ones, but it grows best in moist conditions. This catholicity in what was originally a rain forest tree is also found in other cultivated Meliaceae including Melia azedarach. Although intolerant of shade, Chinese Toon is tolerant of road-salt and can withstand extreme weather conditions, including droughts, so it is excellent as a street tree, as can be seen in not only Paris, but also Philadelphia and elsewhere. It can exhibit clear yellow autumn colour.

It is important not to disturb the ground around the tree, as any damage to the roots promotes the production of root suckers which can be a nuisance. When mature (for example, the best Chinese Toon at Kew, planted in 1907, did not flower until 1947), it produces large trusses of aromatic flowers, followed by characteristic woody capsules, splitting to release wind-dispersed, winged seeds (though fruiting was not recorded in Britain, for example, until 2007 (Anon. 2008). At the Arnold Arboretum, “Despite attempts over the past century, none of the accessions of wild source have survived – almost all have died while in the nursery. I suspect that the very young, juvenile plants (seedlings) were intolerant of those early winters” (Michael Dosmann, pers. comm., Sept. 2021).

Chinese Toon grows very fast, for example, at the Arnold Arboretum, a plant bought from Heritage Seedlings in 1995 is now over 17 m tall and has a diameter at breast height of 30 cm (Michael Dosmann, pers. comm. Sept. 2021). It is rarely attacked by insects, but it is very prone to wind damage when young (Lawrence Banks and Rowan Griffiths, pers. comm. Sept. 2021) and is very susceptible to honey fungus (Armillaria spp.). A grove was established by the author in the Fellows’ Garden at Wadham College, Oxford, the trees being raised by head gardener, Andrew Little, from seeds gathered in the late 1980s from fruiting trees in boulevard St Marcel, Paris. These were collected, rather perilously, by the author leaning out of one of the windows of the Slavia Hotel suite occupied for many years by renowned and much lamented IDS member, the late and inimitable Heino Heine (the effort eased by the sharing, beforehand, of a bottle of Ch. Palmer 1961 from the Wadham cellar). Though well-established, the Wadham grove rapidly succumbed to the fungus, following the death of the large and celebrated purple beech (planted c. 1795), the source of infection in that garden.

At Hergest Croft, Herefordshire, a large tree (in 1995, 23 m tall with a girth of 220 cm at 1.5 m), weakened by woodpecker holes, was stooled in 2004 after becoming dangerous: “We think it may [have been] a favourite of woodpeckers, as the noise that was generated from them banging on the trunk was a familiar cacophony in our azalea garden” (Lawrence Banks and Rowan Griffiths, pers. comms Sept. 2021). “It dated from before 1930 and could have been a [E.H.] Wilson introduction from his last expedition to China, as it was contemporary with other introductions growing there”. Indeed, as early as 1911 Veitch in Chelsea was offering ‘Ailanthus flavescens (Cedrela sinensis)’ plants for 1s 6d to 2s 6d (Hardy Ornamental Trees and Shrubs Catalogue 19: 56. 1911), likely raised from Wilson material.

Overall, the tree seems not to be exceptionally long-lived, the Monticello (see Fig. 13) and Paris experiences suggesting a maximum of c. 130 years or so. It can become a very large tree – up to 40 m in the tropics, though the tallest in a temperate location (Morris Arboretum, Philadelphia) is 31.10 m (though comparatively slender at 190 cm girth). Without doubt it flourishes best in areas with high summer temperatures, with the Mid-Atlantic states being particularly conducive to good growth (as usual). There is a concentration of good specimens in Pennsylvania, including the Morris tree mentioned above, and others at Swarthmore College are also huge (pabigtrees.com – accessed December 2021), but all are exceeded in girth by a very fine tree at Monticello, Virginia, standing 27.10 m tall with a 483 cm circumference (monumentaltrees.com – accessed December 2021). There are many specimens over 20 m across Europe, with a since lost 27 m specimen being recorded in 1957 at Heligan, Cornwall (The Tree Register 2022); perhaps the finest current European specimen is the Belgian champion, in boulevard Leopold, Tournai, at 23 m tall with a girth of 253 cm in 2016 (P. de Spoelberch pers. comm 2021). In Britain the current height champion, at Frensham Hall, Surrey, was 23 m (176 cm girth) in 2010, while at Glasnevin a 17 m specimen with an impressive 319 cm girth in 2012 is the Irish girth and height champion (Tree Register). A tabulation of other significant specimens is presented by Mabberley (2022).