I think one of the most under-appreciated and undersold bloom happenings of early spring in this part of the world are the various maple tree blooms. We like big flowers and we cannot lie, right? However, maple flowers are fascinating to study up close (at least to this crazed plant nerd, who spent an entire year studying flower and mating systems in his undergrad). I love how a maple tree bloom just lights up with a red or orange haze when backlit with spring sun. That, along with vivid green grass, is a huge part of how I remember early spring in the Midwest. 

Maples, members of the Sapindaceae family, are very interesting members of the Acer genera. Maples are notoriously hard to study, making it hard to nail down their pollination strategies and how to classify/describe them. Rather than fitting into a convenient box, maples fill the spectrum of flower types and strategies.

Norway maples produce perfect flowers with all the boy and girl parts in the same flower of every flower on every tree. Acer negundo (boxelder) are dioecious, producing completely separate male and female flowers on separate trees. Many thought for years Acer rubrum (red maple) was similar to boxelder with male and female plants like gingko or holly. Yet, some trees produce some fruit or produce female flowers without fruit. The size of the plant and the length of observation has made it difficult to study some of the species. It is easy to look at what can be reached easily from the ground. Does its mating strategy change with age? We are not sure. It appears with red maple, at least, it really depends on the individual plant. Some plants in a population may be largely male or female, while others can be a bit of both. In one study, Acer pensylvanicum (striped maple) which can form suckering clumps, showed yet another unique variation. Under observation, a single suckering stem might produce male flowers for several years before producing female flowers for several years before dying back.

For years, it was assumed maples were strictly pollinated by the first insects out and about (that was certainly what I was taught a decade or more ago), but that does not seem to be true. More recently, some have theorized that maples are primarily wind pollinated, supplemented with insect visitations taking advantage of early pollen production, at least in the maples studied. Acer saccharum (sugar maple) in one Canadian study, suggests wind pollination exclusively. 

Maples produce fruit called samara, the winged helicopters we all loved to play with as kids. Interestingly though, maples produce them for the winds that blow, and at least one study discovered sugar maple samaras are capable of water dispersal.

Needless to say, there is much about maples you might not have appreciated or noticed as you have gone about your daily routine. Now is a great opportunity to take a walk through your neighborhood and take a second look at those maple trees we have ignored until autumn was upon us. 

Josh Steffen, Horticulture and Facilities Manager