Manitoba Maple - Acer negundo - Érable negundo

So the most recent tree to go into full bloom here in Montreal is Acer negundo (Manitoba maple). The long, pendulous male flowers are quite eye-catching at the moment.

Acer negundo staminate inflorescences

Like Acer saccharinum, A. negundo is wind-pollinated. Unlike A. saccharinum, A. negundo is dioecious [1,2,3], which means that each tree is either male or female. As with A. saccharinum (and other wind-pollinated species), the flowers are not perfumed or showy, as there is no point in investing energy in characteristics which are used exclusively to attract pollinators. Instead, wind-pollinated plants invest energy in producing a huge amount of pollen to make up for the tremendous inaccuracy of wind-pollination.

Acer negundo staminate inflorescence

A. negundo is introduced in this region, being native to places in the U.S. and in central Canada [native range map here]. This tree is a popular choice for landscaping, and because of this has been spread globally. This species takes very well to disturbed habitats and so has a tendency to spread in human-occupied land. A. negundo also prospers in riparian areas (transition zone from land to river). The species spreads easily and is naturalized in southern Quebec, New Brunswick, Nova Scotia, PEI, and various parts of the United States [3].

A. negundo staminate inflorescence

There is some variation in the timing of emergence of flowers and leaves in A. negundo, depending on geographical (climate) factors [3]. In some places, the flowers appear first, and then the flowers. As can be seen in the photos I have, at least here in Montreal, the flowers and leaves appear simultaneously; this is likely related to the shorter growing season here compared to more balmy southern climes.

A. negundo staminate inflorescence

Unlike most maples, A. negundo has distinctive compound leaves. Image of leaves here.

Silver Maple - Acer saccharinum - Érable argenté

So E and I went for a stroll over the weekend and enjoyed the sight of the maples beginning to bloom. Acer saccharinum (silver maple) appears to be the most forward of the maples in our area, already blooming exuberantly.

Abundantly blooming Acer saccharinum

Acer saccharinum is an interesting plant. Although it is a member of the angiosperm (animal-pollinated) lineage, this particular group has returned to wind pollination as a reproductive strategy (pollination syndromes). This fact shows very clearly in the floral morphology (flower shape).

Acer saccharinum - staminate (male) inflorescence. Note the absence of large petals or sepals, and the long stamens which expose the anthers to wind currents. The pollen produced is small and lightweight, which improves its airborne distance.

Acer saccharinum - pistillate (female) inflorescence. Yes, those little fuzzy red protrusions are pistils. They are fuzzy and relatively large in order to best sift pollen from the air.

Anemophilous (wind-pollinated) plants lack sepals, petals, nectar, and perfumes (note that some, like these, can have small or underdeveloped petals or sepals). This is because all of these function to attract pollinators and take up a lot of metabolic energy to produce. So, plants which don't need to attract pollinators will quickly see selection pressure favour inconspicuous, lower-energy flowers. Instead, they invest energy in producing larger quantities of pollen, since wind dispersal is a very imprecise method of fertilization. As a result, the staminae tend to be long and exposed, putting the anthers (pollen-producing portion) in the way of potential wind currents. The pistillae tend to be large and fuzzy in order to better sift and capture airborne pollen.

Acer saccharinum staminate inflorescences

Acer saccharinum is a monoecious plant, but is flowers are unisexual. This means that male and female gametes (pollen and eggs) are both produced on the same plant, but each flower produces either male or female gametes. Note that so far in my observations the trees produce either male or female flowers but not both, but this may vary from year to year; I will defer to the various experts who indicate that this species is monoecious and assume that the individual trees can produce flowers of either sex, and but may express only one in any given year; this also is monoecy. This kind of sex alternation by season has been observed in a number of plants including Arisaema triphyllum.

Acer saccharinum staminate inflorescences

They may not be the showiest flowers in the world, but I love the fluffy, fuzzy appearance of maple trees in full bloom. I find them quite beautiful. Of course, that means that I wouldn't survive long as a pollinator -- I'd waste all my energy visiting flowers that have no reward!

Fortunately for me there's a grocery store nearby, so my poor choice in flower won't reduce my own fitness.