Acer metcalfii Rehder

Much intrigue has surrounded Acer metcalfii, especially as plants bearing this epithet have been introduced to collections at various points over the last three or so decades. Originally described as a species by Rehder (1933) as part of his appraisal of Chinese members of Acer section Macrantha, it was reduced to a subspecies of A. sikkimense by de Jong in van Gelderen et al. (1994), though this was done without observations being made of living material. Rehder (1933) considered it closer to A. davidii subsp. grosseri (then A. grosseri) and the authors of the species’ account in the Flora of China appear not to agree on where the species should be placed, with Chang suggesting that it should be synonymised with A. davidii subsp. grosseri, with its southerly distribution seemingly the character by which its distinction is upheld, but Chen disagrees with this point of view (Xu et al. 2008). Some affinity, at least, to this taxon, is more convincing than placement within A. sikkimense, as along with its green bark and three-lobed leaves it has slender pedicels (Xu et al. 2008), as opposed to the stout pedicels possessed by A. sikkimense.

What appears to be authentic Acer metcalfii is however present in collections, from material of CDHM 14701 collected on Daming Shan, Guangxi, and growing at the David C. Lam Asian Garden, Vancouver, planted in 2015 (D. Justice, pers. comm. 2020). Here it has attained 3 m in height with stems that are ‘deep green burnished red with faint striping. The leading shoots are slender and sparsely branched, and the short, nearly perpendicular laterals and their buds are slender and more red than green. Many of the leaves still look pretty flimsy and narrow (earlier, some of them looked almost like those of juvenile A. caudatifolium) but with age the leaves are gradually starting to adopt the classic A. metcalfii geometry’ (D. Justice, pers. comm. 2020).

Similar plants grow at Tregrehan, Cornwall, while CMBS 843, from Hunan, and growing at the Sir Harold Hillier Gardens, Hampshire, also exhibits comparable foliage, with both entire and three-lobed leaves present (A. Coombes, pers. comm. 2020). CMBS 862, also from Hunan, grows happily in numerous collections, including at Hergest Croft, Westonbirt, and Wynkcoombe Hill Arboretum in the United Kingdom, forming trees of good growth with arching branches. More mature than the aforementioned collections, an affinity to A. davidii subsp. grosseri is very apparent in trees of CMBS 862. Further study into the relationships of these taxa is certainly warranted. Putative hybrids between A. metcalfii and A. davidii are in circulation.

Trees labelled L962 grow at Hergest Croft and are tentatively identified as A. metcalfii, which they do resemble in some respects, however they are not a perfect fit for this species. An added confusion is that L962 was originally collected as A. davidii and other trees raised from this number, for example those growing in Ray Wood at Castle Howard, are very typical of that species. More investigation is needed as the Hergest trees have been extensively propagated and distributed bearing the number L962. This account will be supplemented once these investigations are complete.