Quercus × heterophylla F.Michx.

The Bartram Oak originated as a single tree growing by the Schuylkill River near Philadelphia, USA. John Bartram, one of the first practising Linnean-era botanists in North America, first noted its unusual heterophylly in the mid-18th century. Its mixture of lobed and unlobed leaves complicated early taxonomic placement and delayed formal description. In 1802, François André Michaux examined the specimen during a visit with William Bartram and, in 1811, published it as Quercus heterophylla, recognising it as a distinct species and differentiating it from morphologically similar taxa such as Q. laurifolia. This interpretation was quickly challenged. In 1814, Frederick Pursh argued that the presence of only a single known individual suggested a hybrid origin rather than a valid species. His critique initiated a century-long debate in which numerous botanists assigned the tree to a wide range of possible species or hybrids. The original specimen was removed around 1842, but acorns collected beforehand allowed the lineage to persist in cultivation and naturalised plantings across the Mid-Atlantic. According to Bean (1976), Michaux had also collected acorns and sent them to France, so some cultivated trees in Europe may descend from the original tree. By the late 19th century, most botanists associated the Bartram Oak closely with Willow Oak (Q. phellos), though opinions differed regarding the second parent. Hollick (1888) seems to have been the first to propose Q. rubra as the other parent, based on observations of trees on Staten Island. In 1905, an experimental propagation effort at the New York Botanical Garden produced seedlings spanning the morphological range between Willow Oak and Northern Red Oak (Q. rubra), providing strong evidence for a hybrid origin. Modern genomic analyses have since confirmed this conclusion (Crowl et al. 2020).

There are notable specimens in gardens in the US, for example, in the campus of West Chester University outside Philadelphia (33 m × 160 cm dbh) (Crowl et al. 2020), and in the Sarah P. Duke Gardens, Durham, North Carolina (pers. obs. RC 2024). The UK Champion is at the Royal Botanic Gardens, Kew, planted in 1926 and 23 m × 68 cm in 2022, and a slightly smaller tree, but with a larger girth, used to grow at Borde Hill, West Sussex, measuring 21 m × 70 cm in 1977 (The Tree Register 2025). This tree was apparently received from Rovelli’s nurseries in Pallanza, northern Italy, as ‘Q. viridis’ and identified at first as Q. × morehus before being recognised as Q. × heterophylla. It measured 17 m × 58 cm in 1967 and had more than doubled its girth in twenty-two years (Bean 1976). Larger specimens grow in European parks, the tallest recorded at Wooldrickpark, Enschede, the Netherlands (26.6 m × 127 cm in 2021) and the tree with the largest trunk diameter at Forstbotanischen Garten, Hannoversch Münden, Germany (137 cm dbh and about 15 m tall in 2024). A particularly elegant specimen graces the banks of the Wörlitzer See in the Gartenreich (Garden Realm) Dessau-Wörlitz, Saxony-Anhalt, Germany (see photos below), and measured 19 m × 49 cm in 2015. It is said to be a descendant of Q. × heterophylla grown by John Bartram on his property (Monumental Trees 2025; Russell 2016).

The epithet chosen by Michaux is ancient Greek and means ‘having different leaves’, from ἕτερος (héteros, ‘different’) + φύλλον (phúllon, ‘leaf’) (Wiktionary 2025).