What: Quiz Time! This seems to be the hardest part of the year for telling which trees are which: the buds are bursting, becoming unrecognizable, and the little leaves, just emerging, haven't quite yet taken full shape. It's like looking baby photos of friends and trying to guess who they are. The leaves in the photos below are some of the early ones to come out. Roll over each to test your ID skills (there are both shrubs and trees).
Ecological notes: You can compare the male boxelder shown above to the female boxelder from my post on boxelder bugs. Also, the last photo shows the seeds from an ornamental Siberian elm in Centennial Woods. Ryan Morra and I were pondering over greenness of the seeds. One possibility is that they're actually photosynthetic when they're young (boxelder, white pine, oaks, walnuts, and probably other seeds that invest a lot in endosperm are also green when young). I would imagine that this would take away pressure on the leaves to produce energy for the developing seed. In the elm photo it's a fly on the seed, but other pests can destroy a seed. If leaves were producing energy for growth, winter storage, and the seed, they might be more likely to be at a net loss each year. Having seeds responsible for their own growth is energy insurance for the rest of the plant.
Spoiler alert: The species above are, in order, Populus tremuloides, Cornus alternifolia, Rhamnus cathartica, Acer rubrum, Rhus typhina, Acer platanoides, Acer negundo, Acer negundo, Ulmus pumila.
Other notes: Just a pattern I noticed - willow family and maple family seem to be among our earliest trees to leaf out. Big-tooth isn't out yet, birches are barely opening up, and the buds on some of our more southern species are only beginning to open (e.g. walnut, oak, hickory)