Some thoughts on ecology, evolution and economics

The Maple Leaf Forever

Canadians are passionate about the maple leaf. This is curious since, as a plant species, the sugar maple is not representative of the country.  In fact, maples, in their various forms, are common throughout the northern hemisphere.  So, why Canada? Sugar maples are a common hardwood along the shores of the St. Lawrence River, where Canada was first settled by Europeans. But their adoption as a symbol had more to do with two rather magical properties. The first happens in the fall with the changing of the colors.  Maples are particularly adept at producing red pigments called anthocyanins.  It is thought that these chemicals serve as a sunscreen for plants preparing to absorb nutrients from their leaves before they fall. Whatever the reason, the transformation of the countryside is breathtaking.  About six months later, another magical event occurs.  The freeze-thaw cycle of early spring creates a vacuum in tree stems that sucks the sap stored in its roots up the long vascular tubes that make up the trunk.  This would have been an unnoticed physical phenomenon except for the high sucrose content in maple sap. Indigenous people noticed mammals and birds feeding on the sap leaking out of wounds and broken branches on maple trees.  They learned to collect and concentrate the sap into a late winter food.  Maples – particularly red maple and sugar maple – produce large volumes of sweet sap, making them the preferred source in North America.  It should be pointed out that sugar palms in Southeast Asia are perhaps more deserving of the sugary name.







There are 141 species of maple in the genus Acer, yet another example of a rapid speciation event. The leaves of about a third of these species are featured in a beautiful volume entitled The Book of Leaves.  The book features the leaves of 600 tree species from 22 families.  Chestnut trees are in the same family as the Maples and both Basswood and Eucalyptus trees  are in closely related families.  What is remarkable is how varied the shape and size of maple leaves are from around the world.  All  of the leaves on this page are maples! The typical tree leaf has a single main vein from which other veins branch off.  Other leaves, including many maples, have several main veins radiating out from a central point in the shape of a palm leaf. This pattern is called palmate venation. In maples, these main veins end in leaf extensions or points.  Five of the maple species in this book have only one point  and so, are not palmate at all.  At the other extreme are Acer truncatum from China, with 15 points, and Sugar, Silver, and Big leaf maples from North America, with 13 points.  Maples also vary in the size of their leaves, the smoothness of their leaf margins and their shrubbiness.

Maples from around the world (Click to enlarge)

This graph shows 47 of the maple species from around the world on axes that combine a variety of distinguishing characteristics.  Species that are similar to each other are close together on the graph but basically those on the right have larger leaves (Acer grandifolium from Western North America being the largest) and those higher up on the graph have more points on their leaves (Acer truncatum from China being the pointiest).  The two species that loom large in eastern Canada and came to be the model for the leaf upon the flag, sugar maple and red maple, show up in the top right quadrant as being fairly large and fairly pointy.

Whether Canada’s maples stand out or not is perhaps besides the point.  They certainly made an impression on the first Europeans to live on this land and became a part of the collective identity of Canadians.