Acer sterculiaceum Wall.

Originally described from Nepalese material, Acer sterculiaceum was reportedly so-named for its foliar similarities to species of Sterculia, a genus known as the tropical chestnuts and belonging to the Mallow family, Malvaceae. Sterculius, or Sterquilinius, was a Roman god of manure, whose name may also relate to the species: crushed leaves reportedly emit a pungent scent, however some are fortunate to not be able to detect this scent! From this character comes the common name of Pungent Maple, though any experimental leaf crushing should be undertaken with caution, as the fine hairs present on plant parts of this and other members of Section Lithocarpa can be irritant to the skin.

The typical form of Acer sterculiaceum was introduced to Britain in 1835, from material collected by Sir Joseph Hooker in Sikkim (van Gelderen et al. 1994). Van Volxem reportedly introduced it to Germany in 1850 and Rehder (1927–1940) notes its introduction to North America as being sometime before 1850.

Wild observations of typical Acer sterculiaceum include those made by Roy Lancaster in 1971, whose travels in Nepal with Len Beer and Dave Morris were subsequently documented in Plant Hunting in Nepal (Lancaster 1981). Lancaster saw examples to 10 m tall, growing with other maples including A. pectinatum, A. acuminatum and A. campbellii, as well as with Magnolia campbellii. The trio collected A. sterculiaceum under BL&M 307 Bean (1976) though no plants growing under this number have been traced.

Records of the species from Vietnam are absent from regional floras, but it occurs sporadically around the Sapa area, including close to where Aesculus wangii is found (pers. obs.). Here it is threatened by forest loss (Crowley 2018) and introductions from this part of the range have not been encountered in research for this account.

Acer franchetii is the most frequently encountered species belonging to section Lithocarpa grown in collections in our area. However, the identification of plants to subspecific rank has become confused over time, with botanical texts offering conflicting characters to distinguish the two. For instance, in their account for the Flora of China, Xu et al. (2008) state that subspecies franchetii has leaves that are usually three-lobed, or rarely five-lobed, whereas van Gelderen et al. (1994) state that the same subspecies has leaves that are five-lobed or remotely three-lobed. The two are most usefully separated by scrutinising leaf size: those of the typical subspecies are larger (midveins 10–15 cm in subsp. franchetii, 15–30 cm in subsp. sterculiaceum (De Langhe & Crowley 2018). The typical subspecies may also be confused with the related A. thomsonii, while subsp. franchetii has also been confused with A. tsinglingense (Aiello & Crowley 2021). The accounts of both should be referred to for further details.

The tallest example of subsp. sterculiaceum in the UK grows at Westonbirt in Gloucestershire, measuring 19 m tall in 2024 (The Tree Register 2025). A male tree growing west of Savill Glade in the Old Arboretum and planted in 1942, it is accompanied by a slightly smaller female which fruits reliably and in abundance and is the source of numerous seedlings that appear beneath it. Seed raised plants from this tree also provide rootstocks for grafts of other members of Section Lithocarpa. Plants of 16 m tall grow at Abbotsbury Subtropical Gardens, Dorset and at Hergest Croft, Herefordshire, while the tallest example growing in Scotland is an individual at Cluny House Gardens, Perthshire, measured at 15 m in 2017 (The Tree Register 2025). Material collected by Tony Schilling in 1977 and referred to by Bean (Schilling 2284) grows in the Valley Gardens at Windsor Great Park, measured at 13 m tall in 2021 (The Tree Register 2025).

Noted as ‘difficult to grow in Western Europe’ by van Gelderen & van Gelderen (1999), the typical subspecies appears to be seldom recorded in collections outside the UK. A single specimen is recorded at Arboretum Wespelaar, Belgium, sourced from Plantentuin Esveld, The Netherlands. Proving to be a stubborn grower, it evidently favours moister conditions, appearing to flourish in spring 2025 following a wet 2024 (K. Camelbeke, pers. comm. 2025). While a young plant at Westonbirt performed impressively during the excessively dry summer of 2025, older plants fared less well. One indvidual had dropped all of its leaves by September (pers. obs).