Liriodendron chinense and tulipifera

I saw a young Chinese Tulip Tree, Liriodendron chinense (Hemsley) Sargent,  on the KMOTT visit to the Hill Farm Oast Arboretum garden on July the 7th, a fairly young tree but well established as most trees there are.

The flowers are similar to the American species, Liriodendron tulipifera (L.), if perhaps rather less orange and colourful, but the leaves of the tree are more attractive, with clear waists between two neat pairs of lobes, as also often seen in coppice shoots of tulipifera.  The RHS describes it as potentially bushy, with flowers only found on mature trees, and they claim usually propagated by grafting, which is a surprise. It may not be quite as hardy as the American species, and tends to be grown only occasionally in the UK, although planting is now increasing. It is said to be a bit smaller than the American tulipifera, which grows very large, one of the tallest trees in American woodlands. Its native range is mid-China, extending down to Vietnam, but it is decreasing rapidly due to logging and habitat loss.

Liriodendron chinense has been awarded the RHS's Award of Garden Merit, AGM. The leaves in this species flush a bit red-purplish unlike tulipifera, and there is always good reliable golden-yellow autumn colour, as in tulipifera. There is also a cultivar called J.C. Raulston, from North Carolina, with larger and darker leaves.

It wasn't seen by a westerner until 1875 and was then introduced to the west by 'Chinese' Wilson in 1901, at the turn of the 20th Century, and there are actually no known further introductions of seed until 1977 when seed was gifted from Ninjing Botanic Gardens to Kew, although several seed introductions since then have allowed it to be more commercially available and more widely planted. Seed can even be found on Amazon and eBay.

There are now said to be only two remaining (extant) sister species of the old genus Liriodendron, which are said to have diverged in the late Miocene period. Liriodendron is a genus in the primitive Magnoliid group within the Angiosperms, which is now thought to be quite ancient and separated from the much larger groups of the Eudicots and the Monocots.

Genetic diversity analyses of the DNA suggest that L. chinense has tenfold higher genetic diversity than L. tulipifera, suggesting that the complicated regions comprising east–west-orientated mountains and the Yangtze river basin (especially near 30° N latitude) in East Asia offered more successful refugia than the south–north-orientated mountain valleys in eastern North America during the Quaternary glacial period.

The same paper also suggests that L. tulipifera lies in between the Eastern and Western clades of L. chinense. I cannot quite see how that makes sense in terms of two divergent sister species. There are  also interspecific hybrids as one might expect.