Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

A Red Maple Education

Thursday, May 1, 2014

I have lived with red maples all of my life. As a child I played with the seeds, or samaras as they are called. I have climbed the trees, dropped the samaras from a height and watched as they helicopter to the ground*. I have paddled under the red maples that hang over the river bank. I have watched the leaves turn color in the fall and collected the pigments responsible for this color change. In short, I thought I knew the red maple pretty well. But of course, in nature there is always so much more to learn.
My recent red maple education came about when a friend complained of an early spring allergy from tree pollen. When I asked what trees in particular were producing pollen at this early date, she mentioned that it was largely pollen from the red maple tree. That’s when I realized that although I was familiar with the maples’ trunk, leaves and seeds, I knew almost nothing about its flowers. I decided to take a closer look.

The red maple is one of the first trees to flower in my back yard. When I think of early spring bloomers, I think of forsythia and spicebush. This year - the first year I actually paid attention -the red maple beat them both. The problem is that the red maple flowers are usually high in the treetops and, as they rely mostly on wind for pollination, they are rather small and inconspicuous.
Fortunately for my education, one of the red maples in my back yard has a lot of young shoots growing from its base - a common occurrence in red maples. These branches were in flower and the flowers were just at eye level. How convenient! I collected a few flowers and placed them under the microscope for a good close look. What I saw surprised me. As I expected, I saw the flower’s anthers, the male part of the flower that produces the pollen grains. However, no pistil. No female part to the flower. Did the pistil form later, after the anthers had passed so as to prevent the flower fertilizing itself? Or, like some trees, were there separate male and female trees. That’s when I realized how little I actually knew about the red maple tree. Time to do some research.

I found a paper entitled, The Sex Life of The Red Maple by Richard Primack, a Biology professor at Boston University. Just what I was looking for.

In the study, Dr. Primack monitored the flowers of 79 red maple trees over a period of years. This is what he found:
The red maple has two types of flowers. One flower type contains both female and male male red maple flowerparts but the male parts are greatly reduced in size and non-functional. Therefore it is considered a female flower. The other flower type has both male and female parts but the female parts are greatly reduced in size and non-functional. It is considered a male flower.
female red maple flowerSo that is why I did not see the female parts in the flower I was observing. I was looking at a male flower with the pistil - the female parts - present but greatly reduced. One question answered. But another question raised. Would this tree with the male flowers I was observing also produce female flowers, making the tree monoecious - both male and female at the same time? Or was this just a male tree, and if I kept looking, would I find a female tree, a condition called dioecious where a tree is either a male or a female?

Dr. Primack’s study continues...

Of the 79 trees studied:
53 had only male flowers every year. These trees are obviously male trees.
12 trees had only female flowers every year, obviously female trees.
So far, so good.
But 6 trees that had only male flowers most years occasionally produced some female flowers as well.
6 trees that had only female flowers most years occasionally produced some male flowers as well.
These trees could be considered mostly male or female trees, but not always.
Then finally, there were 2 trees that produced only male flowers some years, only female flowers other years and a few years had a mix of male and female flowers. These trees could be considered male, female and both at different times in their lives.

As I sit at my computer writing this story, the red maple flowers have passed. The trees are starting to leaf out and soon the samaras will be forming. I plan to continue my red maple education early next spring by monitoring the flowers of all the red maples in my back yard. Will I, like Dr. Primack, find more male trees than female trees? If so, is there a reason for this? Do environmental conditions determine the sex of a tree? Or is it just genetics? So much more to learn.

* Samaras have the heavy seed at one end and a thin vane at the other, causing it to twirl as it falls to the ground.