A tree of great vigour; ultimate size unknown. Petiole 5–18 cm. Leaves flushing briefly reddish-bronze; 6–20 × 6–23 cm, with usually 2 pairs of moderately deep, forward-pointing lobes near the base; apex quite shallowly lobed. Tepals 5 cm, the inner 6 overlapping to form a cup-shape; yellow with an extensive orange flush.
USDA Hardiness Zone 6
RHS Hardiness Rating H6
The hybrid between the American and Chinese Tulip Trees was first made in 1963 and then again in 1965 by Professor Y. Pietzung at the Nanjing Botanical Garden in China (Parks et al. 1983), and was reproduced by Clifford R. Parks at the University of North Carolina, USA, in 1973 and 1977. The cross was made again at the Holden Arboretum in Ohio, USA, in 1999 (Holden Arboretum 2018). A scion of Parks’ favourite seedling (‘18–10’) was planted at the Arnold Arboretum, Massachusetts in 1981 and was named ‘Chapel Hill’ after the University of North Carolina’s campus; another plant of ‘18–10’ went to Piet de Jong, Director of the Utrecht University Botanic Garden, and was planted at the Von Gimborn Arboretum (then a part of the garden); it is from this tree that the grafts sold in Europe as ‘Chapel Hill’ were first taken (de Jong 2013).
Most specimens of this hybrid are stil young and vigorous – often extremely so. It is too soon to say how they will appear as mature trees and how it will be possible to distinguish them from the parents in maturity. Grown in China, however, these hybrids pose a potential threat to the genetic integrity of the already threatened wild species (CABI 2018; IUCN 2018).
It is probable that other clones will arise in addition to those described; they may or may not achieve wide circulation. One such is ‘T. Jackson’ (sold in Poland as ‘Jackson’ by Future Gardens and other suppliers), which was also considered to be a hybrid clone by the RHS Plant Finder in 2005.
‘Chapel Hill’, selected by Clifford Parks, is at present the default form of the cross in Europe, at least. It exhibits hybrid vigour, with a tidy conic habit so far, and large leaves that show the attractive reddish flush of the Chinese species, plus larger flowers, which inherit the brighter yellows and orange of the American parent; these are produced from an earlier age (usually within ten years), while the newer clone ‘Doc Deforce’s Delight’, can flower from its fourth year.
Although available from several nurseries in Europe, information on this cultivar remains scarce. Standard information provided is that it flowers in 4–8 years as a grafted young tree, and that new leaves have the strong purplish colour associated with this hybrid.