There are just two species of tuliptree (Liriodendron), and they originate from opposite sides of the globe. Native to much of the eastern United States, L. tulipifera is commonly known as tuliptree, tulip poplar, or yellow poplar. The other species, Chinese tuliptree (L. chinense), grows in small, scattered populations from central to southeastern China. The two species look quite similar but can be told apart by their leaves (those of L. chinense are more deeply lobed) and their tulip-shaped flowers (the bright orange blotches on the petal-like inner tepals of L. tulipifera flowers are lacking in L. chinense). This genus is an excellent example of the disjunct floras of eastern North America and eastern Asia, in which surprisingly similar species are found in these two far-separated regions.
The two Liriodendron species would never have a chance to grow next to each other in nature, but thanks to human intervention they are now planted together at the Arnold Arboretum and many other botanical institutions. They are close enough genetically that they can be cross pollinated by hand, resulting in hybrid tuliptrees. A majestic specimen of this hybrid (L. tulipifera × L. chinense, accession 584-81-A) dominates the eastern edge of the lawn in front of the Arboretum’s Hunnewell Visitor Center and is blooming now. It was received (as a plant) from the University of North Carolina’s Coker Arboretum in 1981. Plant breeders there crossed the two species and, in a happy bit of reciprocity, the L. chinense they used as a parent had originally been sent to them by us. The hybrid tuliptree shows intermediate characteristics from both parents (see the flowers of all three in the photo on p. 12 of this article) and has become a tree of interest for forestry in China thanks to its hybrid vigor.