Acer Griseum, with Its Ibeautiful Copper-Red Bark, Bright Autumn Colour, and Usefulness in a Diversity of Settings, Would Certainly Make It

plant exploration

f there was an ‘A-list’ for trees, then Acer griseum, with its Ibeautiful copper-red bark, bright autumn colour, and usefulness in a diversity of settings, would certainly make it. This well-loved tree is a garden favourite, so it was a shock to see it on the cover of BGCI’s Red List of Maples (Gibbs & Chen 2009). Having known and promoted this plant for years, I had not stopped to think that it is endangered in its endemic range in central China. With this in mind, starting in 2013, I began a project, along with several colleagues, to determine whether the genetic diversity of A. griseum in cultivation adequately reflects that of trees in the wild. We would then see if further conservation efforts needed to be made. This project became a journey through the history of the introduction and distribution of paperbark maple into Western cultivation. It was also an exploration of the current status and range of the species across its distribution in China. What developed was a project that has taken me to the UK, both coasts of the US, and across central China. The goal was to take All photographs by Anthony S Aiello leaf samples for DNA of cultivated trees of known origin and compare them to plants from as many native populations as possible. Over the years numerous authors have extolled the virtues of A. griseum, Acer griseum and one of the best of these is from Vicary Gibbs (1929), who wrote that, ‘the nearest approach to a perfect tree that I can think of, in cultivation which indeed owns “every virtue, every grace”…is Acer griseum, which carries lovely foliage with a dove- and in the wild coloured underside, gorgeous autumn colour, polished golden-brown stem Anthony Aiello looks at a popular maple and shown to him who has seen the sun shining through the shreds of and starts a project to investigate its genetic separated, but not yet dropped, nut- diversity in China and in US and UK gardens brown bark, a sight for the Gods’.

250 December 2016 PlantsmanThe

They are many impressive specimens of paperbark maple at Dyffryn Gardens in Wales (left, above left and above right), and all will be subjected to DNA analysis. Introduction history seedlings at the Veitch nurseries listed it for sale in their 1912 Acer griseum was first collected in (Wilson 1925). It is this collection catalogue, under the heading ‘New 1892 by Père Paul Guillaume Farges that forms the basis of the majority Hardy Plants from Western China’. (#955) near Chengkou in Chongqing of plants now in Europe and the US. Two years before that it was stated municipality. Based on Farges’s In February 1903, less than two (Anon 1910) that ‘Messrs. J. Veitch collection, Franchet (1894) years after Wilson collected seed, & Sons have sent a very fine described it as Acer nikoense var. Augustine Henry (1903) described collection of Chinese trees and griseum before it was elevated to A. griseum as ‘a most remarkable shrubs, including the following rare a species by Pax (1902). tree’, and mentioned that plants and interesting species:- Acer Living material was twice were in cultivation at the Veitch griseum’. Curiously, VN Gauntlett & introduced to Western cultivation Nurseries at Coombe Wood. Only Co, Japanese Nurseries, of Surrey by Ernest Wilson; by seed (Wilson/ three years later, Henry wrote that listed A. griseum in its catalogues in Veitch #1291) collected in 1901 these ‘young plants at Coombe the early 1910s. Because there is no through James Veitch and Sons Wood are about 3 feet high’ (Elwes evidence of introductions other than Nurseries, and two seedlings & Henry 1906). For those of us who Wilson’s, I can only speculate that (Wilson #719) in 1907 for the have struggled to germinate and Gauntlett was serving as a broker, Arnold Arboretum. Wilson (1913) grow A. griseum, it is hard not to envy perhaps proffering plants that describes an encounter with these early descriptions. Henry is originated at other nurseries. A. griseum and wrote that ‘Maples often mentioned (e.g. Veitch 1906) As gardeners became more in variety are very common, but one as having collected A. griseum in his familiar with A. griseum they large tree of Acer griseum, with its travels, but I can find no document continued to write about its value in chestnut-red bark, exfoliating like ation that supports this claim. the garden. Charles Sargent (1919) that of River Birch, was the gem of It was not long until A. griseum wrote ‘This is the most distinct and all’. The 1901 seed collection was an started to make its way from the handsomest of the Maples auspicious one, with unusually good Coombe Wood into various introduced from China in recent seed germination, resulting in 100 collections. Veitch Nurseries first years which have proved perfectly ➤

December 2016 251 plant exploration hardy in the [Arnold] Arboretum, but unfortunately it is still extremely rare in western gardens’. This rarity was bemoaned by Euan Cox (1924) who wrote that the supply of A. griseum simply did not meet its demand, and that trees were just beginning to produce viable seed, nearly 25 years after its introduction.

Highly recommended Despite this, by the 1920s paperbark maple was slowly becoming established in gardens, earning an Heritage Seedlings is the largest grower RHS Award of Merit in 1922 and of Acer griseum seedlings in the US Award of Garden Merit in 1936 (Hunt 1980; this AGM was re- plants. The sampling simply consists Gardens (Vale of Glamorgan, conferred in 1993). By this time, of taking one or two leaves, and Wales), Hergest Croft wanting to set down the story of its preserving them in silica gel for later (Herefordshire), Westonbirt discovery, Wilson (1925) wrote that, DNA extraction and analysis. Arboretum (Gloucestershire, ‘It was May, 1901, that I first saw There are a few known instances England) and Highdown Gardens A. griseum and straight-way became of American trees that were (West Sussex, England). Many of captive to its charms. Looking over purchased from Veitch Nurseries. these collections include original my notes I find the terse statement – These include four trees at Highland introductions from China, and “Hupeh’s best Maple”. Now, twenty- Park, Rochester, New York, one together they provide an intriguing three years afterwards and with fuller tree at the Morris Arboretum, and insight into the world of collecting knowledge of the flora of Eastern two trees at the Arnold Arboretum, 100 years ago. Asia, I do not find my judgement at Massachusetts, that had been A few trees and locations made a fault, though it might be enlarged to propagated directly from 1901 great impression. Among these were read “China’s best Maple” ’. Wilson trees. In addition are two a number of paperbark maples at Unlike other plants that follow trees at the Arnold Arboretum that Dyffryn Gardens, managed by the the vagaries of fashion, a half century Wilson collected as seedlings in 1907. National Trust since 2013. If ever after its introduction, paperbark Other than this, I know of no there was an epicentre for A. griseum, maple continued to be sought after other wild collections until the then it is Dyffryn, which not only and widely recommended. If botanic 1994 North America China Plant holds the UK champion paperbark garden records are any indication of Exploration Consortium expedition maple, but numerous other broader trends in horticulture, then to Hubei. Ten of the seedlings impressive specimens, many of those at the Morris Arboretum in collected are still alive at the Morris which would be champions in their Pennsylvania, where I work, Arboretum, Arnold Arboretum and own right in any other location. illustrate the interest in A. griseum. the US National Arboretum. One of the most remarkable Plants were added to its collection plantings from the mid 20th century nearly every decade from the 1940s UK specimens is the avenue of trees that lines the to the 1980s, but mostly sourced For the next phase of this project, drive at Hergest Croft in Hereford from cultivated plants. Kris Bachtell of the Morton shire. These trees were received Arboretum, Illinois, and I visited from WJ Marchant nursery in American trees venerable A. griseum specimens Dorset and planted in the mid 1950s As mentioned above, this project throughout the UK in July 2014. (Lawrence Banks, pers. comm.). began in 2013 with sampling of The gardens that we visited included Sir Frederick Stern (1957) wrote American trees, focusing on those Royal Botanic Garden Edinburgh that ‘The best colouring maple in the known to have come from Wilson’s (Scotland), Newby Hall and Gardens garden is Acer griseum…the leaves collections plus other wild-collected (North Yorkshire, England), Dyffryn turn a wonderful colour of bronze-

252 December 2016 PlantsmanThe

An avenue of Acer griseum at Hergest Croft was planted in the 1950s (above left). The specimen at Highdown (above) and the one at Westonbirt (left) are from the Wilson 1901 collection.

The third tree is perhaps the most intriguing one. It stands in the rear garden of one of George Forrest’s many homes (Lancaster 2008) which abuts the yard of the botanic garden. How it got there is something of a mystery but it is an impressive specimen.

In the wild In September 2015 we completed the next step of the project, which was to sample wild populations of A. griseum across its native range in red and gold in the autumn and it is A. griseum conservation project. central China. Together with Kris attractive all the year round with its At Westonbirt Arboretum, Bachtell, Michael Dosmann (Arnold brown-red peeling bark’. The young among the extensive Acer collection, Arboretum, Massachusetts) and plant that Stern purchased from is a lovely open-grown A. griseum near Kang Wang (Beijing Botanical Wilson’s 1901 collection is a their Down Gate. After examining Garden), I explored within an beautiful specimen, albeit uprighted their records we realized it was from approximate 800km radius of and staked after the gale of 1988, at the Wilson 1901 collection. Xi’an, the capital of Shaanxi Highdown in Sussex, the garden he Finally, at RBG Edinburgh, there province. Our travels took us to established. This tree is testimony were three A. griseum of great paperbark maple populations in to the longevity and durability of interest. The largest and best known five provinces: Chongqing, Henan, A. griseum, and serves both as an of these stands across from the Palm Shaanxi, Shanxi and Sichuan. important source of germplasm and House, while nearby is a tree The trip was especially an insight into the conservation received in 1938 from Admiral Sir informative because we witnessed value of living and documented (Archibald) Berkeley Milne, an avid a wide range of conditions and collections. It was one of the most horticulturist, who commanded the habitats across the range of impressive trees that I visited in British Mediterranean Fleet at the A. griseum. In total, we came away summer 2014 as part of the outbreak of the First World War. with 66 samples of paperbark ➤

December 2016 253 plant exploration

In deciduous forest in Henan The largest specimen seen in China many paperbark maples cling was this one in Shaanxi, just left of tenaciously to rock outcrops the centre of the photograph maple, from nine locations in five competing with Quercus aliena. provinces. Visiting the isolated Another location was in southern populations, often a day’s drive apart, Shaanxi. Although only 70km as provided a graphic understanding of the crow flies from the site in what it means for a species to be Chongqing, even with modern endangered. In some of the sites we highways and countless tunnels, it encountered trees scattered across a was an eight-hour drive through wide area, while in other sites there mountainous countryside. In this was a high density of trees in a case we were looking for a tree restricted area. In most situations (designated SHX-018) that was we encountered very few young described on the 1995 NACPEC seedlings, indicating a possible expedition (Meyer 2010). Driving reason for the species’ decline. We three hours south from the city of also observed that there was great Angkang we arrived in the small uniformity in the leaf shape, bark, village of Long Shan Cun at Baixian and habit of trees, something that is Forest Station. It did not take long also seen among cultivated plants. to find the same massive tree, There were many highlights on a growing next to a small farmhouse trip such as this. One was in along with several seedlings. This Chongqing, near where Farges had was by the far the largest tree that we been in the 1890s, where a group saw in China; it first branched at 4m, of trees grew on a hazardously had a diameter at breast height of steep slope covered in loose shale. 84cm, and was 30m tall. An added Although on private land, and bonus in this village was finding an despite being coppiced for firewood enormous Corylus fargesii, from for several decades, they had re- which we were excited to make a The first branches of the large sprouted and maintained remarkable seed collection (Aiello 2016). specimen in Shaanxi emerge at 4m above the ground vigour, stretching for light and A third population, in western

254 December 2016 PlantsmanThe

Henan, was near where Josef Hers American seedlings Analysis collected a number of herbarium The sampling phase of the project Now all sampling is complete, specimens between 1919 and 1924. concluded in July 2016 when I Dr Andrew Hipp of Morton Near here, we visited Baotian Man visited the Pacific Northwest in Arboretum will be analysing the Nature Preserve. Here, in a beautiful the US. There I visited Heritage DNA of the cultivated trees to mixed deciduous forest of Acer Seedlings (Salem, Oregon), the answer our first question of how davidii, Carpinus cordata, North Willamette Research Station much genetic diversity is represented C. turczaninovii, Cornus kousa and (Aurora, Oregon), and Washington in cultivation. Early results support Quercus aliena subsp. acutiserrata, we Park Arboretum (Seattle, the idea that Wilson’s 1901 first encountered paperbark maples Washington). collection provides the basis for all as we had come to expect them – Heritage Seedlings is the largest trees in the UK and most of what perched on the edge of rock grower of paperbark maple seedlings had been in the US in the 20th outcrops and stretching for the light. in the US. They have produced century. Once we have full results But then we found the healthiest 200,000 since 2011, and similar we can make decisions about the population of our trip. Growing for a numbers since the late 1990s (Eric next steps for conservation efforts. few hundred metres along either side Hammond & Mark Krautmann, of a small stream valley was a group pers. comm.). Although our Conclusion of well over 100 trees. These were molecular work should sort this Working with A. griseum has of all sizes, from seedlings and mid- out, the original sources of seed at provided an opportunity to explore sized trees a few centimetres in Heritage Seedlings were two older collections that were assembled diameter, to mature specimens as trees at North Willamette Research during the ‘golden age’ of plant large as 37cm diameter at breast Station of unknown origin, seed collecting. It has led me to height. This area was unlike anything from Highland Park Arboretum fascinating places across the US, that we had seen previously, with the in Rochester, and perhaps trees UK and China, which in turn have mixture of sizes and ages indicating a that came from Beijing Seed demonstrated the value of cultivated healthy population actively Company that were probably plants in helping to preserve an recruiting young seedlings. collected in Henan. endangered species. One of my impressions of references A. griseum is of its longevity and Aiello, AS (2016) Corylus fargesii: a Lancaster, R (2008) Plantsman’s resilience, with plants more than 100 rare tree-forming hazel, with Paradise: Travels in China. Garden Art years old showing excellent health. exfoliating bark. Curtis’s Bot. Mag. Press, Suffolk But this should not be mistaken for 33(2): 48–59 Meyer, PW (2010) Paperbark maple, Anon. (1910) V. Miscellaneous notes. Acer griseum. Arnoldia 6(2): 48–50 complacency. A message to all Bull. Misc. Inform. Kew: 24 Pax, F (1902) Aceraceae. In: Engler, A gardeners is that it is easy to Cox, EHM (1924) Supply and (ed.) Das Pflanzenreich. 8 Heft (IV 163): underestimate the conservation demand. The Garden 88(2765): 771 29 value of even familiar garden plants. Elwes, HJ & Henry, A (1906) The Sargent, CS (1919) Unfolding leaves. The Franklin tree (Franklinia Trees of Great Britain & Ireland. Vol. 3. Bull. Popular Inform. Arnold Arbor. n.s. alatamaha) is perhaps the best Privately printed, Edinburgh 5(2): 5 example of how collections in Franchet, A (1894) Plantes nouvelles Stern, F (1957) Gardening on chalk. botanic gardens and private gardens de la Chine occidentale. J. Bot. 8(17): J. Roy. Hort. Soc. 82: 370–378 290–297 Veitch, JH (1906) Hortus Veitchii. can preserve a species. However, Gibbs, D & Chen, Y (2009) The Red J. Veitch & Sons, London with increasing threats to natural List of Maples. Botanic Gardens Veitch, J & Sons (1912) New Hardy habitats, an old friend such as Acer Conservation International, Surrey Plants from Western China (introduced griseum has great conservation value Gibbs, V (1929) Robinias at through Mr. E.H. Wilson). J. Veitch & in cultivation. Aldenham and Kew. J. Roy. Hort. Soc. Sons, Chelsea 54: 145–158 Wilson, EH (1913) A Naturalist in Anthony S Aiello is the Gayle Henry, A (1903) Chinese maples. Western China. Methuen & Co., Gard. Chron. ser. 3. 33: 100 London E Maloney Director of Horticulture Hunt, DR (1980) Acer griseum. Curtis’s Wilson, EH (1925) Acer griseum. The and Curator of the Morris Arboretum Bot. Mag. 183: 13–15 Garden 89(2773): 20 of the University of Pennsylvania.

December 2016 255