Virtual Museum of Canada
Jardin botanique de Montréal 
Centre for Forest Research

Location, location, location

The leaves of every tree species are positioned at precise locations along the twigs. If they are opposite, two leaves face each other; if they are alternate, they are staggered; and if they are verticillate, they are arranged in whorls. Similarly, our arms are positioned opposite each another; the teeth of a zipper alternate; and the spokes of a wheel are verticillate (they’re all attached to the axle at the same height).

This difference in construction provides an additional clue to a tree’s identity. However, since trees regularly lose their leaves, it’s important to be careful and observe several locations in order to avoid jumping to conclusions. Can you identify the various leaf arrangements in this photo?

Photomontage of alternate leaves of a blue beech (Carpinus caroliniana), of opposite leaves of a mountain maple (Acer spicatum), and of verticillate leaves of a Northern catalpa (Catalpa speciosa)
1. Carpinus caroliniana / 2. Acer spicatum / 3. Catalpa speciosa
© Jardin botanique de Montréal (1. Robert Mineau / 2. Normand Cornellier /
3. Lise Servant)