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This relatively well-known species was described by Bean (B211, S47) and Krüssmann (K82) under the name Acer mono. After considerable debate as to the nomenclature of this taxon, Ohashi (1993b) demonstrated that A. pictum is the correct name, and he recognised 11 subspecies with numerous forms. The following two taxa appear to be distinct and have been recently introduced, but it is possible that others of Ohashi’s rather poorly differentiated subspecies are present in cultivation.
The only known introduction to cultivation of this taxon was a collection of seed under the number SICH 1107 made at c.2660 m near Muli, Yunnan, by the Sichuan Expedition of 1992. The parent tree was a fine 15 m with a trunk of 90 cm dbh, growing in mixed deciduous forest. Seedlings did not become established at Kew, and although one grew at Quarryhill for 12 years this has now been killed by Armillaria (H. Higson, pers. comm. 2007). No others have been traced.
Rarity has added piquancy to the interest in this taxon, but fortunately it would seem that the report of only 15 surviving specimens (van Gelderen et al. 1994) is an underestimate, as Kirkham & Flanagan (2005) record it as a principal constituent of woodland they visited in South Korea in 1989. There, on the island of Ullung-do, it is a large tree up to 20 m tall, with wide-spreading branches. Seed from this expedition (KFBX 168) has given rise to a very vigorous specimen at Kew, 8 m tall in 2005 (Flanagan & Kirkham 2005), but there are several other large specimens in the United Kingdom as well, including one that was 9 m tall when measured by Owen Johnson for TROBI in 2003, at Batsford Park, Gloucestershire, and one that has reached 10 m at Hergest Croft (planted in 1985). The Hergest Croft tree is a fine individual with ascending branches, although it is prone to depredations by squirrels. Another large specimen (9–10 m) grows at Chevithorne Barton in Devon. Both of the latter trees are derived from a collection made in 1982 by James Harris and Joe Witt, from which only two seeds germinated (J. Harris, pers. comm. 2006). Viable seed is now produced in cultivation. In North America it is growing at the Arnold Arboretum and elsewhere. At the David C. Lam Asian Garden, a 12 m tall tree, grown from seed collected by Ferris Miller in 1980, has an 18 m spread of branches; Peter Wharton commented that it is ‘very, very vigorous’ (pers. comm. 2007). It is not fully hardy in Poland (P. Banaszczak, pers. comm. 2007).
The leaves of all the A. pictum subsp. okamotoanum seen have had an elegant poise with upturned lobe tips, enhanced by a slightly undulate margin. They emerge light red and turn a good yellow in autumn. It grows very well on alkaline soils (J. Harris, pers. comm. 2007).