Most of you already know bigleaf maple. It’s hard to miss this tree with its giant leaves, and being in Canada, we all know what a maple leaf looks like. The scientific species-name ‘macrophyllum’ is descriptive: macro (Greek) = large, phyllum / phull (Greek) = leaf. Maple syrup is made from the sap of a different species of maple, usually the sugar maple (Acer saccharum) that grows in Eastern North America.
Walking among tall trees, it can be difficult to see the foliage. So you should be able to identify bigleaf maple based on its trunk and bark. A complementary strategy, is to look for the remnants of last year’s leaves on the ground underneath the trees. If the bark looks right, and you find large-sized maple leaves under the tree, then you’re probably dealing with Acer macrophyllum.
The trunks of bigleaf maple are often covered in a thick layer of mosses, and oftentimes licorice fern (Polypodium glycyrrhiza) grows as an epiphyte in the moss on the trunk. Photo credit: Douglas FraserMore mossy trunks of bigleaf maple. Often, bigleaf maples have several trunks growing from the base of the tree, as shown in this image. The bark, where exposed, is greyish-brown and ridged. Photo credit: Douglas Fraser
The leaves of bigleaf maple are very large, ranging from 15-30 cm across. They are attached in pairs, opposite to each other, at the leaf nodes along branches.
Bigleaf maple leaf. Note the five lobes and distinctive veins radiating from the base of the leaf. The leaves are often around 30 cm / 11 inches wide. Photo credit: Douglas FraserThe leaf stalks (petioles) of bigleaf maple are often reddish. They will release a milky sap if cut. Photo credit: Douglas FraserAttachment of leaf stalks to a young shoot. Note that the leaf arrangement is opposite; there are pairs of leaves, oppositely positioned at each leaf node. Photo credit: Douglas Fraser
Bigleaf maples flower quite early in the spring, so you won’t encounter flowers when you look at this species in the Fall semester. Within each cluster of flowers, some flowers only have male pollen-bearing structures (stamens), while others only have female, egg-bearing structures (ovaries). This condition, of both types of unisexual flowers on the same plant is called ‘monoecious’. (mono (Greek) = single, oikos (Greek) = house). Compare this to the situation in trailing blackberry (Rubus ursinus): there, male flowers are borne on ‘male’ plants and female flowers are borne on separate ‘female’ plants. This condition is called ‘dioecious’ (di (English) = two, oikos (Greek) = house).
An inflorescence (cluster) of bigleaf maple flowers. Most of the flowers shown in this image are male – they only have pollen-bearing stamens. Some of the flowers higher up in the cluster might be female, lacking stamens but containing two fused ovaries. Photo credit: Douglas FraserThe flowers near the top of the inflorescence flower-cluster) are female and carry two ovaries each, each containing a single egg-bearing ovule. The little red “beaks sticking out of these flowers will develop into the wing-portion of the fruit as it matures. Photo credit: Douglas Fraser
The fruits of the bigleaf maple are the familiar “maple keys”. You may have played with these as a kid (or you still do).
Cluster of bigleaf maple fruits. The technical botanical name for this fruit-type is ‘schizocarp’, or even more precisely ‘samaroid schizocarp’ – but you don’t need to memorize that detail for the purposes of our Botany course. Photo credit: Douglas FraserThe non-fleshy (i.e. ‘dry) fruit of bigleaf maple (and other maples) consists of two ‘achenes’ fused together. The embryos reside in the thick parts in the center. When the fruit detaches from the tree, the thin papery wings allow the structure to helicopter and drift through the air away from the mother plant. Compare this strategy to that of the Douglas-fir seed (Pseudotsuga menziesii), which has a thin papery wing too. Photo credit: Douglas Fraser
Parts of bigleaf maple have been used by First Nations people for technology (e.g. the wood for paddles) and medicine (e.g. to treat sore throats).
