OK, I've got this now. Two threads included discussions about distinguishing Liriodendron tulipifera from L. chinense: November 22, 2012 - More yellow October 29, 2013 - Yellow (again) I'm pretty certain I've been identifying these reliably on the basis of hairs on the leaf backs. Here are Liriodendron tulipifera leaves from today from two different locations in the Carolinian garden. Note the very short bristly hairs on the primary, secondary and even tertiary veins. They make the leaf backs feel rough. This Liriodendron chinense leaf I picked up from the ground last week in the Asian Garden has no bristly hairs anywhere and the papillae on the underside of the leaf surface make it feel slippery, even as old a leaf as this was. Here is a better photo from last year, a leaf from one of the city locations. Since the posting in which I thought the UBCBG tree was the only one in the city, I have found five locations in Vancouver with several L. chinense, all confirmed by seeing the flowers. I wonder if the papillae have something to do with the L. chinense being much less attractive to aphids. Or maybe the aphids just slide right off the slippery papillae. Well, I like the image of that. Unrelated to that discussion, here's a photo from today of L. tulipifera, showing what the Vancouver Trees app describes as stipules having a somewhat duck-billed shape, enclosing (I love this description) "a miniature preformed leaf folded longitudinally and bent downward on a tiny, curved petiole, encircling a smaller stipular bud that encloses another leaf encircling a still smaller bud (and so on)."
I'm adding another leaf-back comparison of the two species, from the entrance plaza outside Dr. Sun Yat-sen Classical Chinese Park, where there are seven Liriodendron chinense and one L. tulipifera (that surely was supposed to be the same as the other seven). There were flowers today, but they were mostly finished and none were close enough for me to get good photos. I have seen all these trees previously with flowers. Here is Liriodendron tulipifera, showing the short bristly hairs mentioned in the first posting, on the veins, but no hairs on the leaf abaxial surface. The photo below is Liriodendron chinense, with much less prominent veining on the back of the leaf, though that wasn't as obviously the case for all the leaves. There are no bristly hairs, and the leaf surface is silky smooth.
Nina Shiroplova has sent me flower photos to make this thread a little more complete. Liriodendron tulipifera Liriodendron chinense
