Quercus × runcinata (A. DC.) Engelm. ex Sarg.

This hybrid was described from a specimen collected by Georg Engelmann in the Mississippi bottom-lands near St. Louis. It was growing with Q. rubra, Q. imbricaria, and Q. palustris, and was originally regarded as a form of Q. rubra. It was said to differ from Q. rubra in its smaller fruits and the toothed but not lobed leaves, and was suspected of being a hybrid (Engelmann 1877). Engelmann sent it to de Candolle under the name Quercus × runcinata, indicating he thought it to be a hybrid between Q. rubra and Q. imbricaria, but de Candolle described it in 1864 as a variety of Q. rubra. He mentioned in his description that it could be a hybrid, but that he was unable to distinguish the specimen provided by Engelmann from Q. rubra. Gray listed it as Q. rubra var. runcinata Engelm. in 1868, also suggesting that it was probably a hybrid. Engelmann published it as a species in 1877, but in his description admitted that the leaves of Q. rubra are so variable that de Candolle had correctly considered it to be a variety of Q. rubra. This means the name was published as a synonym and was hence invalid. The name was not validly published till Sargent validated it in 1922, stating that it was ‘believed to be a hybrid.’ Trelease (1917, 1924) seems to have had no doubts that it was the hybrid between Q. rubra (as Q. maxima) and Q. imbricaria, a conviction shared by Palmer (1948): ‘there can be little doubt that Engelmann’s plant and numerous later discoveries are really hybrids of the parents he first suggested.’

Notable trees in the UK include the champion for girth and height growing at the Royal Botanic Gardens, Kew, accessioned in 1973 and measuring 23 m × 85 cm in 2022. Other large trees are at the National Botanic Gardens, Glasnevin, Ireland (14 m × 36 cm in 2012), Chevithorne Barton, Devon, (11 m × 19 cm in 2017), Wynkcoombe Arboretum, West Sussex, (8 m × 13 cm in 2017), and the Sir Harold Hillier Gardens, Hampshire, where a tree from seed collected in Illinois in 2000 was 9.5 m × 16.2 cm in 2023 (B. Clarke, pers. comm. 2023; The Tree Register 2025). In Belgium at the Arboretum of Daniel Dumont, Lesve, it has reached 17 m × 44 cm (Snyers 2011). In the US, a large specimen at Oak Ridge Cemetery in Springfield, Illinois (see below) is proclaimed as the state champion on the cemetery’s website, though it appears hybrids are not included in state rankings (Oak Ridge Cemetery Foundation 2025; Illinois Extension 2025).

The epithet runcinata is Latin from runcinare, meaning ‘to plane’, as a carpenter planes wood (Mahoney 2025), from ancient Greek ῥυκάνη (rhukánē, ‘plane, a carpenter’s tool’), of unknown origin (Wiktionary 2025). In botany it is used to describe leaves ‘having tooth-like projections pointing away from the apex’ (Wiktionary 2025). Neither Engelmann nor de Candolle provided a derivation for the epithet, but Gray mentions that the leaves have ‘less deep and more ascending lobes.’