Paulownia tomentosa (Thunb.) Steud.

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Credits

Owen Johnson (2022)

Recommended citation
Johnson, O. (2022), 'Paulownia tomentosa' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/paulownia/paulownia-tomentosa/). Accessed 2024-04-21.

Common Names

  • Foxglove Tree
  • Princess Tree
  • Empress Tree
  • Royal Paulownia
  • Kiri
  • Mao Pao Tong

Synonyms

  • Bignonia tomentosa Thunb.
  • Paulownia imperialis Sieb. & Zucc.
  • Paulownia imperialis var. lanata Dode
  • Paulownia tomentosa var. lanata (Dode) Schneid.
  • Paulownia recurva Rehd.

Glossary

taxonomy
Classification usually in a biological sense.
USDA
United States Department of Agriculture.
concolorous
Having the same colour throughout.
dbh
Diameter (of trunk) at breast height. Breast height is defined as 4.5 feet (1.37 m) above the ground.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
taxon
(pl. taxa) Group of organisms sharing the same taxonomic rank (family genus species infraspecific variety).

Credits

Owen Johnson (2022)

Recommended citation
Johnson, O. (2022), 'Paulownia tomentosa' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/paulownia/paulownia-tomentosa/). Accessed 2024-04-21.

Tree to c. 25 m, sometimes spreading widely from a short bole. Leaves always large, matt and hairy, dark or bright green, broadly or narrowly cordate, sometimes shallowly lobed. Flowerheads to 50 cm tall, with many short branches. Cymes with 3 or 4 flowers; peduncle 1–2 cm and nearly as long as the pedicel. Calyx lobed to more than half its length. Corolla whitish to purplish, 5–8 cm long, the lower lip longitudinally ridged. Fruit-capsule ovoid, 3–5 cm long, dense with sticky hairs; wall c. 1 mm thick. (Hong et al. 1998).

Distribution  China Anhui, Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, S Liaoning, Shaanxi, Shandong, Shanxi South Korea Planted and possibly native

Habitat A pioneer species growing below 1800 m in the wild and widely naturalising.

USDA Hardiness Zone 6

RHS Hardiness Rating H6

Awards AGM

Conservation status Not evaluated (NE)

Paulownia tomentosa has been the default representative of its genus for nearly two centuries in Europe and North America, and for much longer in Japan and Korea. It is the species best able to cope with cooler growing seasons, and the most likely to naturalise aggressively (Ecosystem Gardener 2022).

The tree was described by Carl Peter Thunberg (as Bignonia tomentosa) in his 1784 Flora Japonica: Paulownia tomentosa had long been grown in Japan, both as an ornament and for its valuable fire-retardant timber, and it was traditional to plant one upon the birth of a daughter, so that it could be felled to provide the wood for her marriage-chest or tansu (Roman 2016; Wikipedia 2022), a valuable item whose contents were protected by the timber’s resistance to both fire and damp (Elwes in Elwes & Henry 1906–1913; Li & Oda 2007; ipaulownia Sustainable Forestry 2022). Seed was sent (from Japan to Holland) by Philipp von Siebold in 1829–30 (Jacobson 1996), but may not have survived the long sea voyage; a second consignment of Japanese seed reached France in 1834, where a single plant was germinated by Joseph Neumann within the hothouses of the Jardin des Plantes in Paris (Bean 1976; Philadelphia Historic Plants Consortium 2012). In the following year, Siebold, writing with Joseph Gerhard Zuccarini and apparently unaware of Thunberg’s description of the tree, named it Paulownia imperialis to honour Anna Paulowna, Crown Princess of the Netherlands.

After a couple of years, Neumann found that his sapling did better outside, even in the cold winters of 19th century Paris; it flowered for the first time in 1841, providing an abundance of seed for the European market, although in 1838 there had been another importation of seed from Japan to England (Bean 1976). By 1843, P. tomentosa had reached Parsons’ Nursery in New York (Philadelphia Historic Plants Consortium 2012).

In warmer climates, Paulownia tomentosa is neither the fastest nor the straightest member of its genus and has been little used for forestry, although several modern hybrids use its genes to combine a better tolerance for short summers with a degree of hybrid vigour. Another of these hybrids, REVOTROPIX® has been selected and extensively used in the tropical climate of Malaysian Borneo (Pim 2021), helping to indicate just how tough and versatile a plant the genes of P. tomentosa can produce.

Particularly in northern Europe, the common form of Paulownia tomentosa tends to be a widely domed tree seldom much more than 15 m tall; its trunk is usually short and may be crooked or forking. Its leaves are a rather dark – some would say dull – green, and almost as broad as long, sometimes with four shallow lobes that make them approximately pentagonal; its flowers are a rich and dark bluish mauve, paler inside. It seems likely that this genotype derives from the species as selected over the centuries in Japanese gardens, from where all the first importations of seed to the west were made; such forms were distinguished as var. japonica by Henry John Elwes (GBIF Backbone Taxonomy 2022), but this taxon is no longer recognised by modern authorities (Hong et al. 1998). (See the entry under Japonica Group, below, for a further discussion.) Around the turn of the 19th and 20th centuries, at least two seed collections were made from the wild population within central China, and the resulting stock (Lilacina Group, and ‘Wilson’s Giant’ – q.v.) tends to make straighter trees with paler mauve flowers and with fresher-green leaves which are slender and elegantly long-pointed; as such they are more likely to be confused with the taller species from southern China, such as P. fortunei. Another distinctive genotype, deriving from trees long cultivated and possibly growing wild in Korea, is described here as the Coreana Group (q.v.), but it should be noted that only plants with a speckled yellow throat are referable to this. Not all Korean plants fit Coreana Group, as demonstrated by a collection by Bleddyn and Sue Wynn-Jones from Ulleung-do island between South Korea and Japan (BSWJ 8503) with concolorous flowers (illustrated below). Crûg Farm’s own specimen had grown to five metres by 2016, in a rather cool climate (Tree Register 2008).

The usual forms of Paulownia tomentosa are hardy to USDA zone 6; at the Morton Arboretum in Illinois (zone 5b) plants are often killed back to ground-level (Dirr 2009). One specimen does survive much further north in the Annapolis Royal Historic Gardens in Nova Scotia, Canada (Annapolis Royal Historic Gardens 2011), where it flowers around the end of May. The flower-buds, which are exposed through winter half-developed within woolly, individual buds, tend to be killed by about 20°C of frost (Dirr 2009). In a less continental climate, without long warm summers to ripen the new growths, the tree is considerably less hardy and may be difficult to establish; writing a century ago, W.J. Bean suggested that even at Kew it was necessary to overwinter seedlings for their first year under glass (Bean 1976).

Today, established trees are usually sufficiently happy to become worthwhile flowering trees across the whole of Wales and of much of England and Ireland. In 1998, a young six-metre specimen was blossoming well at Faaie Mooar in the very Atlantic climate of the Isle of Man (Tree Register 2022). Within the slight heat island of The Hollies park in northern Leeds (West Yorkshire), a specimen has really thrived and was 14 m × 73 cm dbh in 2020 (Tree Register 2022). In Scotland, just one respectable tree is known so far: happily situated next to the air vents of the laundry room under the south wall of the Perth Royal Infirmary, in one of the warmest parts of the country, this was 13 m × 53 cm dbh in 2017 (Tree Register 2022). The emphatic UK champion is a tree planted after 1947 in the rich, deep and fertile soil of Bute Park in Cardiff – the warmest part of Wales – which was 21 m × 131 cm dbh in 2013 (Tree Register 2022). These dimensions are, however, far surpassed by trees in continental climates: the USA champion, planted as long ago as 1926 at the Reitz Memorial High School at Evansville in Indiana, was 21 m × 243 cm dbh in 2022 (monumentaltrees.com 2022).

In areas with cool summers where flowering becomes unreliable, the recommended way of cultivating Paulownia tomentosa is to coppice it each winter so that it regrows with great vigour and with spectacularly large leaves. In the very mild winters of Caerhays Castle in Cornwall, meanwhile, it is usual for some of the flowers to open in dribs and drabs from November onwards (Williams 2021). In Queensland, Australia, blossom can be expected in mid August – equivalent to mid February in southern California (GardensOnline 2022).


'Alba'

Flowers predominantly white; in cultivation by 1905 (Jacobson 1996). In 1962 a large tree at Leonardslee in West Sussex, UK, was 11 m × 63 cm dbh (Tree Register 2022), however ‘Alba’ is probably now extinct. White-flowering Paulownia (which also include P. tomentosa ‘Georgia Princess’ and P. ARCTIC®) are seldom quite as spectacular as might be imagined: the corolla tends to retain spots or streaks of purple and yellow, while the large red-brown calyces also muddy the overall impact.


Coreana Group

Common Names
Korean Paulownia

Synonyms
Paulownia coreana Uyeki
Paulownia tomentosa 'Coreana'

Leaves yellowish-green; flowers mauve, with violet spots and yellow throats. (Dirr 2009, Edwards & Marshall 2019).

Distribution

  • North Korea – (?)
  • South Korea

RHS Hardiness Rating: H6

USDA Hardiness Zone: 5

Paulownia coreana was described as a species from Korea in 1925 by Homiki Uyeki, based on the characters given above, but treated as a cultivar by Hu (1959). The speckled and yellow throat seems to be the most significant difference from the usually concolorous P. tomentosa. It is by no means clear whether this is a consistent character in Korean populations, or whether Uyeki’s species was based on a limited, unusual population: Krüssmann (1986), following Hu, crisply states ‘A clone from Korean cultivation, not a species.’ Material collected by Bleddyn and Sue Wynn-Jones on Ulleung-do (BSWJ 8503) and offered as Paulownia tomentosa ‘Coreana’ is concolorous and therefore must be considered to be P. tomentosa var. tomentosa.

More research is needed to establish the true status of this taxon both in Korea and in cultivation. Trees and Shrubs Online would be very grateful for any information readers can provide about this variant with speckled, yellow throats to the corolla. In the meantime, it seems best to consider plants with this characteristic as a Cultivar Group, P. tomentosa Coreana Group. As material in cultivation has been raised from seed a cultivar name is inappropriate, and the epithet has not been validly published at either varietal or forma rank, making them unavailable. A printed description of the Group will follow.

Sir Harold Hillier collected seed in Korea in the mid-1970s (Bean 1976); plants grown at Kew and at the Sir Harold Hillier Gardens had all gone by 2022, but another in the relatively continental climate of the Cambridge University Botanic Garden, accessioned in 1979, was 9 m × 39 cm dbh in 2014 (Tree Register 2022). A slightly larger but younger tree of unrecorded origin was at Thenford House in Northamptonshire in 2019 (Tree Register 2022). In the UK National Collection of Paulownia near Bath, the Coreana Group is represented by a specimen raised by David Ewins from seed collected in 2007 from the Hilliers tree (which may or may not have come true); in 2022 this tree was 8 m × 34 cm dbh (Tree Register 2022). All of these need to be checked while in flower. The Coreana Group is also grown in the United States (Dirr 2009; Hatch 2021–2022), where it should cope particularly well with the harsh winters of the Midwest.


'Georgia Princess'

A sport with white flowers which arose on the University of Georgia campus at Athens, USA (Dirr 2009) but may never have been commercially distributed; it may have represented the same mutation as ‘Alba’ (q.v.). Online images of white-flowering Paulownia tomentosa in the south-eastern United States seem likely to be ‘Georgia Princess’.


'Hulsdonk'

RHS Hardiness Rating: H6

USDA Hardiness Zone: 4b

‘Hulsdonk’ was selected as a seedling by the Dutch nurseryman Cees Hulsdonk: it blooms precociously and tends to be compact and rounded in habit (Ebben 2022). The assessment that it is hardy to USDA zone 4b (Ebben 2022) has probably not been tested.


Japonica Group

Common Names

Synonyms
Paulownia tomentosa var. japonica Elwes

Trees cultivated in Japan, and their descendants; habit often low and spreading; leaves broad and dark green; flowers richly coloured and purplish.

RHS Hardiness Rating: H5

USDA Hardiness Zone: 6

All of the early introductions of Paulownia tomentosa to Europe and North America were of seeds from plants of cultivated Japanese origin, and it seems likely that the familiar forms of the species in today’s gardens, with their low, spreading habit, broad rather dark leaves and rich purplish flowers, all derive from the plants selected in old Japan. The name P. tomentosa var. japonica was published by H.J. Elwes in 1921 to describe this population (GBIF Backbone Taxonomy 2022), but is no longer recognised.

Since this account of Paulownia tomentosa proposes a Coreana Group (to describe trees of Korean origin) and a Lilacina Group (to describe the descendents of at least one collection from western China), a Japonica Group is listed here, for the sake of consistency, to cover all the trees which are likely to derive from the population cultivated in Japan; it will be validated with a printed description in 2022. However, there will probably not be many occasions when using this name is actually helpful, since the origins of many of today’s cultivated Paulownia tomentosa are impossible to prove. One recent collection from Japan is HONX 36, represented at Kew in 2022 by a tree of 13 m × 43 cm dbh, accessioned in 2000 (Tree Register 2022).


Lilacina Group

Common Names
Lilac Paulownia

Synonyms
Paulownia fargesii Hort., not Franch.
Paulownia lilacina Sprague

A tall tree. Leaves fresh-green, rather narrowly cordate, long pointed and very seldom lobed; flowers to 9 cm long, pale lilac with a large yellowish stain in the throat but with few purple spots or none; calyx with unusually short hairs. (Bean 1976; Hatch 2021–2022).

Distribution

  • China – In the western provinces

RHS Hardiness Rating: H6

USDA Hardiness Zone: 5

Seed of this tree was sent to Maurice de Vilmorin’s nursery in Paris by the French missionary and botanist Paul Farges around 1896; in the same year, Adrien Franchet described a new species from the same area of western China as Paulownia fargesii, commemorating Farges who had been the first westerner to collect specimens. It was originally assumed that Vilmorin’s seeds were from P. fargesii, but plants from this stock, flowering at Kew in June 1928, were studied by the Scottish botanist Thomas Sprague, who published the name P. lilacina for them in 1938 (Bean 1976). (Laurence Hatch’s statement that the name P. lilacina was being used by Vilmorin as early as 1905 – about the time when the first French seedlings should have begun to flower and to reveal their true nature – appears to be an error or at least an over-simplification (Hatch 2021–2022).) Contemporary botanists agree that this population represents part of the remarkable natural variation of P. tomentosa, but Hu’s (1959) recommendation that ‘Lilacina’ should be treated as a cultivar name does not suit the apparently authentic wild provenance of the cultivated plants, or their likely genetic diversity. These trees might be best described as a variety or forma, but as these combinations both lack a valid description, a Lilacina Group is proposed here, and will be validated with a printed description during 2022.

In terms of habit, foliage detail and flower colour, plants of the Lilacina Group are more likely to suggest Paulownia fortunei than the ‘normal’ (Japanese) form of P. tomentosa as grown in the west. They can make quite tall and graceful trees, with handsome, long-pointed leaves, and their blooms, opening well ahead of the foliage, are a delicate mauve. Their probable origins in the mountain forests of western China suggest that they should be more at home in a soft, Atlantic climate than most variants of P. tomentosa, and the UK champion indeed grows at Rowallane near the east coast of Northern Ireland (13 m × 81 cm dbh in 2016) (Tree Register 2022). Other specimens have become considerably taller, with one at Dunster Castle in Somerset, since lost, measuring 21 m in 2006 and another at Pencarrow in Cornwall – again, an Atlantic climate – 20 m tall in 2016 (Tree Register 2022).

The Lilacina Group still seems to be quite widely cultivated, both in northern Europe and the United States, although nomenclatural instability continues to make this an elusive plant; it is often still grown as P. fargesii, a species which actually remains exceedingly rare in cultivation. One North American supplier (Oikos Tree Crops 2022) suggests – rather surprisingly, given these plants’ origins – that the Lilacina Group is among the hardiest of all Paulownia forms, untroubled by 39° C of frost.


'Somaclonal Snowstorm'

A variegated sport selected by Dr Michael Marcotrigiana at the University of Massachusetts, USA, in 1984 (Hatch 2021–2022). Its leaves are flecked and streaked with cream but it quickly tends to revert (Dirr 2009) and has not maintained a place in cultivation.


var. tsinlingensis (Y.Y. Pai) T. Gong

Common Names
Guang Pao Tong

Synonyms
Paulownia glabrata Rehd.
Paulownia tomentosa var. glabrata (Rehd.) S.Z. Qu
Paulownia fortunei var. tsinlingensis Pai
Paulownia shensiensis Pai

Leaf-base rounded to shallowly cordate, not deeply cordate; upper surface glabrous or only sparsely hairy (Hong et al. 1998).

Distribution

  • China – Gansu, Henan, Hubei, Shaanxi, Shandong, Shanxi, N Sichuan

RHS Hardiness Rating: H5

USDA Hardiness Zone: 6

Var. tsinlingensis is the only sub-population of a very variable species to be given varietal status by the Flora of China (Hong et al. 1998); it is widely planted in central China. In cultivation in the west, it is represented in Canada at the David C. Lam Asian Garden of the University of British Columbia in Vancouver (University of British Columbia Botanical Garden 2022), and in the United States at the C.R. Keith Arboretum in North Carolina, where it tends to bloom a week or two earlier than typical Paulownia tomentosa (Hatch 2021–2022). Seed from the arboretum of Grenoble University grown at RHS Garden Wisley gave rise to a very fine specimen growing in the Exotic Garden there (M. Pottage pers. comm. 2022) notable for its particularly attractive overwintering buds. It does not entirely match the description provided for var. tsinglingensis, particularly in having pubescent upper surface of the leaves; further investigation is needed. In the UK, it is one of just three wild Paulownia taxa which is not as yet commercially available.


'Wilson's Giant'

Synonyms / alternative names
Paulownia recurva Rehd.

Paul Farges had sent seed from a tree which turned out to have been from the varied wild populations of Paulownia tomentosa in central and western China in the 1890s (see P. tomentosa Lilacina Group); during his first expedition for the Arnold Arboretum in 1907–9, Ernest Wilson collected seed from another tree growing wild in western Hubei (W 769) (Bean 1976). The tall habit and fresh-green long-pointed leaves of trees grown from W 769 recall the Lilacina Group (and also resemble some features of P. fortunei); planted in a sheltered site at the Westonbirt National Arboretum in Gloucestershire, one specimen grew to 27 m tall and lived until 1990 (Tree Register 2022). Original trees from W 769 also thrived at Exbury in Hampshire and Colesbourne in Gloucestershire (Bean 1976), while a P. tomentosa from a Wilson collection had reached 20 m at the Glasnevin National Botanic Garden in Dublin in 1987 (Tree Register 2022).

Although these have long gone, suckers from the Colesbourne tree were distributed by Henry John Elwes (Bean 1976), and when the original tree died around the turn of the millennium two more suckers were singled and quickly made remarkable graceful trees with long straight boles, 18 m and 17 m tall in 2018 (Tree Register 2022). These have been repropagated by Pan Global Plants, and became available in 2022 under the cultivar name ‘Wilson’s Giant’ – a name which should correctly be applied only to scions of the Colesbourne stock but which also commemorates the remarkably tall sister seedling at Westonbirt.

[Editor’s note: the original tree of W 769 at Colesbourne Park died shortly after 2000, and when I arrived as Gardens Manager there in 2003 its logs were still on the bonfire pile. True to its reputation for poor flammability they remained unconsumed for many fires. JMG]