Friday, May 7, 2021

All trees flower

By Larry Cornelis – Sydenham Field Naturalists

Yes, all trees flower.

Some people are surprised to hear that.

Larry Cornelis Photo

Probably because many trees have inconspicuous flowers, easily missed.

Of course, there are trees with very conspicuous flowers too, such as the redbuds I just previously wrote about.

There are trees with large showy flowers and small showy flowers and large and small non-showy flowers (the inconspicuous ones).

In the spring, the trees with non-showy flowers may appear to some people to be leafing out, not flowering.

In mid-April you may look at a wooded area or a tree and see greenish, brownish, reddish and/or mixtures of those colours and assume the colour is from leaves developing but it’s actually the trees flowering.

Right now (May 1) the cottonwoods look brownish/reddish and that’s from the flowers.

Just take a closer look, it’s obvious up close.

There are good reasons for the differences.

It is all about how the flowers are pollinated.

The showy colourful flowers are attracting pollinating insects (see my previous article ‘Supporting Pollinators’).

The insects move the pollen from flower to flower.

Larry Cornelis Photo

Some trees have sweet fragrant flowers to attract bees and such and others have putrid smelling flowers that attract carrion flies and beetles.

The non-showy/inconspicuous flowers are on trees that are wind pollinated.

The wind moves the pollen from flower to flower and tree to tree.

No need for pollinating insects.

Every tree has its own strategy for getting pollinated and producing seed.

It gets more complicated when we refer to a trees sex.

Some are bisexual and some unisexual and weirdly sometimes both.

Here we can get into some very technical scientific words such as dioecious, monoecious, polygamous, polygamonoecious, polygamodioecious and perfect.

Dioecious trees have individuals that are male or female, male flowers with stamens and female flowers with pistils on different individuals.

Larry Cornelis Photo

Monoecious trees have separate male and female flowers on the same individual.

Perfect flowers have both male and female organs in the same flower and polygamous is with flowers sometimes perfect, sometimes unisexual with the sexes borne on the same or different individuals.

The other two long terms are just weird combinations of sometimes perfect, sometimes unisexual, the sexes borne on the same individual or different individuals.

Sorry for the technical stuff but it gives you the understanding of tree sexuality.

Enough said.

As examples, oaks and hickories are monoecious with male and female flowers on the same tree and therefore all produce seed.

Cottonwoods and aspens are dioecious with male and female flowers on different trees, only the female trees producing seed.

Both oaks and cottonwoods are wind pollinated.

On the other hand, showy flowers are perfect, pollinated by insects and every tree produces seed.

But there isn’t always a big crop (mast) of seed with some species of trees.

Some years the trees hardly produce any seed.

Larry Cornelis Photo

There is lots of speculation about why that happens (and different reasons) but it may be to control invading pests.

If trees don’t produce seed for pests (such as weevils) in one year, the pest’s population crashes and then there are fewer pests to attack the seeds in following years.

It is a cycle of mast years and non.

Oaks are a good example of this.

So, this is the time of year to get outside and check out the trees and how they are flowering.

Enjoy the showy and appreciate the inconspicuous, it’s all good.

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