Paulownia kawakamii T.Itô

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David Ewins

Credits

Owen Johnson (2022)

Recommended citation
Johnson, O. (2022), 'Paulownia kawakamii' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/paulownia/paulownia-kawakamii/). Accessed 2023-03-25.

Common Names

  • Sapphire Dragon Tree

Synonyms

  • Paulownia rehderiana Hand.-Mazz.
  • Paulownia thyrsoidea Rehder
  • Paulownia viscosa Hand.-Mazz.

Glossary

Critically Endangered
IUCN Red List conservation category: ‘facing an extremely high risk of extinction in the wild’.
IUCN
World Conservation Union (formerly the International Union for the Conservation of Nature).
article
(in Casuarinaceae) Portion of branchlet between each whorl of leaves.
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).
included
(botanical) Contained within another part or organ.
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

Owen Johnson (2022)

Recommended citation
Johnson, O. (2022), 'Paulownia kawakamii' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/paulownia/paulownia-kawakamii/). Accessed 2023-03-25.

A medium sized tree to c. 15 m, with a spreading crown from a short bole. Leaf cordate, never huge, slightly shiny above. Inflorescence broadly conical, to 1 m tall, with a few long branches. Cymes often 3-flowered; peduncle short or absent. Calyx conspicuously ridged, green-margined, and lobed to more than half its length; in fruit these lobes are often reflexed. Corolla relatively small (3–5 × 3–4 cm). Fruit capsule relative small (2–4 cm long); wall less than 1 mm thick. (Hong et al. 1998).

Distribution  China Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi, Zhejiang; perhaps naturalised from planted trees Taiwan Mountain forests, c. 1800 m; a rare tree

Habitat Forests; and as a pioneer plant.

USDA Hardiness Zone 7b-8

RHS Hardiness Rating H4

Conservation status Critically endangered (CR)

Paulownia kawakamii was first described by Tokutarô Itô in 1912; its name commemorates another Japanese botanist, Takiya Kawakami. Within a genus of fecund and sometimes invasive trees, it holds the unique position of having been assessed as Critically Endangered, having presumably lost out to its more vigorous natural hybrid with P. fortunei, P. × taiwaniana. This assessment was made as long ago as 1998 by Dr Fuh Jin Pan, who knew of just 13 surviving trees surviving within forests in the Chiayang area of Taiwan, which was rapidly being cleared (IUCN 2022; Kirkham & Fay 2009).

Dr Pan’s assessment may have been unduly pessimistic and the situation certainly needs reappraising: In the same year, the Flora of China described a much wider distribution for Paulownia kawakamii, extending across China’s southern and eastern provinces (Hong et al. 1998); its authors did not comment on whether this population is likely to be native, or to have naturalised from earlier plantings. Kirkham and Fay (2009) follow Dr Pan in suggesting that the mainland population must consist entirely of planted trees. (Paulownia kawakamii was independently described by Heinrich von Handel-Mazzetti in 1921 – as P. rehderiana – from a planted tree observed in Ichang by Ernest Wilson.) But it might be considered strange for a species confined to the interior mountain forests of Taiwan to have enjoyed such widespread popularity in areas of China which already had their own various and more vigorous native Paulownia. Since the time of Dr Pan’s assessment, trees identified as P. kawakamii have also been found in other parts of Taiwan; NMWJ 14552 was collected in 2015 by Bleddyn and Sue Wynn-Jones, working with the Taiwan National Museum of Natural Science, in the Wuling area, considerably further north and east (Crûg Farm Plants 2018). If even some of these additional populations do turn out to be native P. kawakamii, it seems unlikely the species will meet the requirements for a Critically Endangered assessment.

The flowers of P. kawakamii are perhaps the most striking of the genus, being heavily spotted and widely open; a tree covered with them is a magnificent sight and place it in the first rank of flowering trees. The opportunity to conserve the genetic diversity of a rare and threatened species has also undoubtedly boosted the popularity of Paulownia kawakamii as a garden tree, at least in the UK: in 2022 the Royal Horticultural Society listed 13 suppliers, making this the second most widely available representative of its genus. Its relatively diminutive stature may also have attracted interest, though here the word ‘relatively’ is important: like other members of its genus this is a vigorous tree whose leaves and flowerheads are built on a massive scale. (The statement in the Flora of China that the leaves of wild trees are no more than 8 cm long (Hong et al. 1998) is surely an error.)

The first introduction to the west seems to have been made during an expedition by the Royal Botanic Gardens, Kew, as recently as 1992, when Tony Kirkham and the late Mark Flanagan collected seed from one of the trees in the Chiayang area which was known to Dr Pan (ETOT 41). Despite the much drier conditions at Kew, two of the trees from ETOT 41 have thrived, with the spreading example next to the Water Lily House, planted in 1995, making a particularly good ambassador for its species; in 2022 this was 14.5 m × 67 cm dbh (Tree Register 2022). Its leaves are slightly shinier than is typical for the genus; the architecture of its abundant flowerheads, with a few long branches, differs from the tower-like structure of the inflorescences most Paulownia species and is emphasised by the way that the relatively small individual flowers are carried close to these branches, in often stalkless clusters of three.

Another collection of Paulownia kawakamii, EN 4600, made by the late Edward Needham and planted at Tregrehan in Cornwall in 2000, has thrived comparably in a much more Atlantic climate, reaching 12 m × 40 cm dbh in 2014 (Tree Register 2022); other recent collections to have been distributed by Crûg Farm Plants have included RWJ 9909 and BSWJ 6784. The specimen in the UK National Collection of Paulownia near Bath, sourced by David Ewins from Fillan’s Plants and planted in 2002, was 11 m × 36 cm dbh in 2022 (Tree Register 2022). At Gorwell House in Devon, the species was planted in 1998 by John Marston and had reached 9 m × 40 cm dbh by 2017 (Tree Register 2022). In the Chelsea Physic Garden – an inner London site where space is at a premium – an example was managed by annual coppicing in 2005, but by 2016 one stem had been singled and had grown on to 8 m (Tree Register 2022). P. kawakamii is not among the hardiest members of its genus; the northernmost good specimen the author has observed was a tree eight metres tall at Matthew Ellis’ Grange Farm Arboretum in the Lincolnshire fens in 2019. In 2000, a seedling Paulownia growing in the tarmac outside the Colchester offices of English Nature (as was) was identified by Chris Gibson from foliage characteristics as P. kawakamii (Gibson 2003), but – even if an early planting had been made nearby to produce the seed – it could be reasonably suggested that a tree which is apparently incapable of perpetuating itself in its own native forests is unlikely to have been able to do so in a carpark in Essex: this seedling was almost certainly P. tomentosa.

As marginally the least vigorous member of a very vigorous genus, Paulownia kawakamii has attracted little interest among foresters, though its hybrid P. × taiwaniana has been widely used in the Far East and the genes of P. kawakamii have also been incorporated in the modern hybrid clones ‘Pao Tong Z07’ and PAULEMIA®. In his 2008 memoir, Californian plantsman Timothy Hall states that P. kawakamii was promoted alongside P. fortunei by the Sapphire Dragon Corporation, in the United States from 1992 and in north-west Mexico from 1995 (Hall 2008), but the flowerhead which illustrates this article and which is captioned as P. kawakamii is clearly not from that species; confusion may have arisen through the vernacular name ‘Dragon Tree’ which has since been applied to both these taxa. What appears to be genuine Paulownia kawakamii has, however, been sold in California since 1997 by San Marcos Growers, who received a single plant in 1994 from the botanist Isabelle Greene (San Marcos Growers 2022). The species is also represented in the cooler climate of the David C. Lam Asian Garden at the University of British Columbia, Vancouver, Canada (TreeLib 2022), and is sold in Australia (GardensOnline 2022).

Although a series of wild collections has allowed Paulownia kawakamii to be grown in the west in some variety, it is unclear whether the sundry sale names which have inevitably arisen represent any significant genetic departures. The 2004 online catalogue of sapphiredragon.com (presumably the same Californian company that was founded to market P. fortunei in 1992, now defunct) listed ‘Jade Dragon’ with white flowers, ‘Lucky Dragon’ with rose-pink flowers, and ‘Sapphire Dragon’ with sapphire-blue flowers, produced from the tree’s third year (Hatch 2021–2022), but further confirmation would seem to be needed that all or any of these clones really represented P. kawakamii. SAPPHIRE DRAGON™ can still be found online as a trade name (perhaps the same as POWTON™); the Royal Horticultural Sociey lists ‘Sapphire Dragon’ (a cultivar name) as synonymous with P. kawakamii (Royal Horticultural Society 2016). Toad Gully Growers, an Australian wholesale nursery with a forestry bias, offers a ‘Sapphire Select’ (Toad Gully Growers 2022), but the accompanying image suggests that this is not true P. kawakamii.