Ivy

Letter number 11 in the tree alphabet is ivy. It's a dependent kind of tree, using others for support, but it surely more than makes up for this by the benefits it provides to other species (shelter and a late-in-the-year food supply). There's nothing quite like a big ivy in full flower in autumn, buzzing with happy bees, who have so little else to feed on at that time of year.

So, here's my picture, complete with flowers (the Y), which are such beautiful subtle structures and go largely unnoticed because of how late they bloom.