Acer campbellii J.D. Hooker & Thomson ex Hiern

Acer campbellii is a broad ranging species, occurring in the eastern part of the Himalayan chain into southwest China, and also in the Central Highlands of Vietnam (though absent in the north of that country). It was first discovered by a collector working for William Griffith in Darjeeling, and first introduced by Sir Joseph Hooker from his Himalayan expeditions (1847–1851), who ‘named it in 1875 for his friend, the Superintendent of the hill station at Darjeeling’ (O’Brien 2018). It has been introduced numerous time since. It appears to be more a warm-temperate species than a truely temperate one, and has thus been considered quite tender in gardens. While of course this is quite true for material from parts of its range, particularly so lower elevations, it has proved hardier when introduced from more suitable provenances, such as at altitude in Bhutan, though in many areas it is still prone to damage by late spring frosts (D. Justice, T. Christian, pers. comms. 2020).

It has elegant foliage with serrulate margins, which help distinguish it from typical forms of the related A. flabellatum. The presence of flowers is always a helpful aid to identification (the floral disk and ovary are pubescent in A. campbellii and glabrous in A. flabellatum), and generally required to separate it from A. flabellatum var. yunnanense, which has similar leaf margins, glabrous disks and, sometimes, slightly pubescent ovaries. Seamus O’Brien paints a vivid picture of encountering A. campbellii during multiple visits to Sikkim, including on Mount Maenam where Hooker would have seen it, and where it ‘formed superb column shaped specimens to 27 m’ in the company of Magnolia campbellii, Rhododendron grande, Acer sikkimense, and Schefflera rhododendrifolia (O’Brien 2011).

Like A. flabellatum, A. campbellii is not so commonly encountered in collections as some other members of section Palmata. DJHC 0518 grows at the Hoyt Arboretum, Oregon, while examples of KR 1688, from Bhutan, grow at the David C. Lam Asian Garden, Vancouver (American Public Gardens Association 2017). Numerous specimens grow at Tregrehan in Cornwall, clearly happy in the Cornish climate, though it can do well further north in the United Kingdom if properly sited. Two young trees grow on the Bhutanese hillside at Benmore Botanic Garden in Argyll, grown on from NPSW 387 collected at c. 2950 m asl in Bhutan. However, attempting to grow it even from the hardiest of provenances at the Rogow Arboretum, Poland, would be ‘a waste of time’ (P. Banaszczak, pers. comm. 2020). Many more gatherings made in recent years bear the name A. campbellii, but it seems prudent to err on the side of caution and only cite those that have been seen and confirmed.

Another, as yet unsatisfactorily characterised taxon, relating to A. campbellii, has been introduced to cultivation on several occasions from the Hoang Lien Mountains of northern Vietnam, including collections of BSWJ 11695, BSWJ 11713, FMWJ 13369 and FMWJ 13374 (Crowley 2018). This has been circulated as A. heptaphlebium, which was treated as a synonym of A. flabellatum (as A. campbellii subsp. flabellatum) by van Gelderen et al. (1994), though it is quite distinct, with broad, shallow, ovate lobes and very large samaras. Its flowers also have petals shorter than the sepals, which in A. flabellatum are as long as one another. Furthermore, within Vietnam, A. heptaphlebium grows far further south than the Hoang Lien Mountains, from where this material has been collected. This interesting, new material, bears resemblance both to A. campbellii and A. flabellatum and is clearly a member of this group. Its predominantly seven-lobed leaves have serrated margins, while its flowers have glabrous disks and pubescent ovaries, similar to those of A. sinense. It has been most collected in its ‘red-leaved’ form, with the leaf undersides vividly, and persistently red, though all-green examples are also present in its habitat, though evidently not as attractive to the collector. Like much material collected in northern Vietnam in recent years, it is becoming established in collections in parts of our area, though the extent of its hardiness is yet to be fully established. It is also important to note that this taxon is not A. campbellii var. fantsipanense, which, despite its name, is quite unrelated and plants collected as this invariably belong to a relative of A. pectinatum in section Macrantha. See the account of that species for further details.