Acer fenzelianum Handel-Mazzetti

Rare in cultivation, as in the wild, Acer fenzelianum appears to be represented in cultivation only by one collection, that of Dan Hinkley, under DJHV 06173, collected in 2006 from Seo My Ty in the Hoan Lien Mountains of northern Vietnam, where it was growing with another maple, A. pictum, as well as various Magnolia species and members of the Fagaceae (D. Hinkley, pers. comm. 2018). Since 2006, the area in which this collection was made has unfortunately been denuded of much of its woody flora due to deforestation and though some taxa are regenerating, neither species was found there in 2018 (pers. obs. 2018). DJHV 06173 came to be circulated under A. tonkinense subsp. liquidambarifolium, a synonym of A. tonkinense, and, as of spring 2020, is listed as available as such at Crûg Farm Plants (2020). It is also being grown at the Elisabeth C. Miller Botanical Garden, Seattle, inside the alpine house, where it has reached c. 2.5 m tall and may soon be moved outside (D. Justice, pers. comm. 2020). While the limits of its hardiness are somewhat untested, and though seemingly tender, a plant of A. pictum grown from seed collected at the same Seo My Ty locality (DJHV 06144) has proved hardy at Westonbirt Arboretum, Gloucestershire (pers. obs. 2020).

It is reasonably assumed that the species is named after G. Fenzel, whose collection, Fenzel 44, collected in Sapa, northern Vietnam, represents its type specimen. However, some taxa bearing this epithet, for example Cyperus fenzelianus, are named for an E. Fenzl (1808–1879), an Austrian botanist and former head of the botany department at the Natural History Museum, Vienna. Thus, reference to Fenzl in relation to the naming of Acer fenzelianum in van Gelderen et al. (1994) is considered to be an error.

Morphologically Acer fenzelianum appears closest to A. tonkinense. This is perhaps unsurprising, given the confusion in the naming of the aforementioned collection, while Murray (1969) had treated A. fenzelianum as a subspecies of A. tonkinense. However, the two species are easily split by the abundant, grey to yellowish pubescence on the petioles, branchlets and inflorescences of A. fenzelianum, which in A. tonkinense, aside from the pubescent disk and ovary, are glabrous. Fang (1939) notes that this tomentum may persist for four years.