Keys - Samaras - Samares

Less than three weeks ago, I started posting about the maple trees in bloom. Well, they've wasted no time! I've been watching the samaras (samara: winged fruit) developing since about May 4.

Acer saccharinum samaras

Acer platanoides samaras

Acer negundo samaras

Samaras are a useful adaptation. Because of the thin, papery 'sail' portion, this seed will travel further from the tree than other types of nuts, allowing better dispersal of seeds and therefore a better territorial expansion for the population. Note that all maple keys are samaras, but not all samaras are maple keys; many other genera of trees produce samara, including the elms and ashes.

The photo below shows a close look on an A. saccharinum samara which was not successfully fertilized and so is not developing (note the small, shrivelled samara on the right-hand side). The tree does not invest energy in developing samaras which are not fertilized, as it would be wasted energy; an unfertilized samara that flies away from the tree won't result in a new tree, so there's no point in investing the energy.

A. saccharnum samaras

In some cases the samaras are developing before the leaves. This tree looks very green and filled out, but all of that green is from samaras, not leaves. Depending on the species, these samaras will take to the air throughout the spring and summer.

Acer saccharinum crown

Signs of Spring: Leaf buds and robin (Turdus migratorius) - Bourgeons et merle d'amérique

A classic harbinger of spring, of course, is the American robin (Turdus migratorius).

This is the first one I've seen this year, spotted in the Notre-Dame-des-Neiges cemetery in Montreal on April 25th. T. migratorius is often one of the first migratory birds to return from winter territories.

T. migratorius on a gravestone; note the A. saccharinum blooming in the foreground and the leaf buds on the shrub in the background

Interestingly, this widespread bird is apparently a major carrier of West Nile virus, contributing to the virus' spread across the continent.

T. migratorius

This particular individual didn't seem at all fazed by our presence, and in fact ended up calmly observing us in return.

Leaf bud opening

The leaves are just starting to emerge now. Here are a few photos of leaves beginning to emerge. The species I've seen already opening buds here in Montreal are Acer negundo, Fraxinus pennsylvanica, and Syringa vulgaris.

More leaf buds

The weather is warming quickly now.

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.