Acer oliverianum Pax

Named for Daniel Oliver, former Keeper of the library and herbarium at RBG Kew, A. oliverianum was first introduced by Wilson in 1901, collected on his first expedition for Veitch Nurseries (Bean 1976a). As observed on herbarium material foliage of his 1907 collection, W. 1936, made while collecting for the Arnold Arboretum, bears resemblance to that of some of the largest trees known in cultivation, that of mature examples at Westonbirt Arboretum, Gloucestershire and in the Valley Gardens, Windsor Great Park. These bear three-, four- and five-lobed leaves, a character that the species is known for, though not all examples exhibit four lobed leaves. The tree at Westonbirt, measured at 13 m tall in 2014 (The Tree Register 2018) is the UK and Ireland Champion and though speculated to be derived from a Wilson collection, this remains unproved and seemingly unprovable. It has a spreading crown though is largely one sided, having grown adjacent to a, now removed, Chamaecyparis lawsoniana of significant dimensions for most of its life.

Several recent introductions of the species have been made, including those circulated under the name of Acer schneiderianum. These include SICH 1214, collected in November 1992 at 2390 m in Zhaojue County, Sichuan. Here the parent trees of up to 8 m in height grew in a rich community of broadleaved trees on a north-facing slope. Good specimens are established at Wakehurst Place and in Giles Coode-Adams’ arboretum at Feeringbury Manor, Essex, the latter being the larger tree, at 9 m in 2019 (O. Johnson, pers. comm. 2019). This collection also grows well at the David C. Lam Asian Garden, Vancouver. There have also been more recent commercial introductions, and the species is offered by specialist nurseries in Europe. Such an example grows at Westonbirt and has formed an attractive, rounded crown, colouring a good orange in late autumn. A plant observed at Hergest Croft has an attractive ‘pewtered’ cast to the mature leaves in summer. This plant originated as seed imported from China by Andrew Norfield – one of several Chinese species introduced to a wider market by his nursery. Based on plants at RBG Kew and Westonbirt, the widely distributed Ogisu 95089, collected in 1995 in Xichang, Sichuan and included by Grimshaw & Bayton (2009) under A. schneiderianum, more accurately belongs to the A. flabellatum affinity (pers. obs. 2018, 2020).

Other introductions include SICH 2393, collected on the final SICH expedition in 2003, at 1680 m in Jiuzhaigou County, Sichuan. This too was made in rich forests on a north-facing slope, on rocky, sandstone soils. This was found in collections by Erskine (2012) growing as A. sinense (or A. campbellii subsp. sinense), though belongs to A. oliverianum. Similarly, SABE 1805, collected in 1980 from the Shennongjia Forest District, Hubei, is grown in some American collections as A. sinense, though also belongs here, as determined by Yousheng Chen from material at the Harvard University Herbarium. Several other collections have been made by American-led expeditions, including QLG 149 and 245, collected in 2006, the former from Liuba County, Shaanxi, the latter from Tian Shui City District, Gansu. Examples of both grow at the Morris Arboretum, Philadelphia, Quarryhill Botanical Garden, California and the United States National Arboretum, Washington D.C. (American Public Gardens Association 2017).