Wednesday, April 22, 2015

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.

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