Wednesday, January 4, 2012

Alders

I have seen so many things in Chicago that I had only previously known from reading about them: Lake Michigan, excellent public transit, Chinese steamed buns, earlobe loops that stretch all the way to the shoulders.  My second favorite (after public transit) is a tree I have always admired: the alder (here you can see the leaves, which aren't available this time of year in Chicago).

Alders are in a fine plant family, the Betulaceae, or birch family.  Birches are marvelous trees despite their small stature.  They have nicely-shaped rounded but toothed leaves, a branched and clustered growth form, and that great bark that you have to resist peeling if you don't want to kill the tree.  In fact, I like birches so well, I named my dog Birch (Botany nerd joke: his Latin name was Betula tomentosa var. lutea).

Alders have all those great characteristics except the peeling bark, but they also happen to have flowering structures that reveal an important evolutionary link.  Remember learning in 4th grade that there are two kinds of trees, evergreen and deciduous?  This distinction divides trees into the two main groups of all plants (except those weird and ancient-looking mosses, liverworts, ferns, and the fern allies).  The two main groups of plants are Angiosperms and Gymnosperms.

Angiosperms all have some type of flower, including those plants with bright, gorgeous flowers, like the tulips and those with small, dull flowers like grasses and oak trees.  Deciduous trees are Angiosperms (though a few Gymnosperms do technically lose their leaves).  Another characteristic of Angiosperms is that they produce seeds inside fruits. I'm using the botanical definition of fruit here, meaning a hard or fleshy container  around a seed, like an apple, tomato, walnut shell or pumpkin.  The term Angiosperm refers to this phenomenon of having seeds enclosed within a structure (angio = enclosed, sperm = seed).

Gymnosperms produce seeds but don't bother to wrap them in anything.  The prefix, gymno-, means naked, which kind of makes you wonder about the word gymnasium.  Gymnosperms  produce seeds in cones, but the cones do not enclose the seeds.  The naked seeds just fall right out of those cones when they are ready to germinate.  Most Gymnosperms are trees, and most of those have needle-like leaves that are evergreen and do not fall in the Fall.

I was really desperate for a picture of a cone here.  Glitter is not natural on cones.


Cones are plant organs with repeated flat things called scales. The cones are either male or female, and their scales produce either pollen (plants sperm) or ovules.  Wind blows the pollen to the ovules, and then the fertilized ovule grows into a seed.  The big cones like the ones pictured above are female cones.  Male cones look a little bit like those strange brown mini corn cobs you sometimes get in Chinese food.  The evolution of Angiosperms from Gymnosperms included the flattening and softening of the cones' scales along with production of pigments and scents.  Flowers are basically cones modified to attract insects for carrying pollen from male to female plant structures.

Alders (I haven't forgotten we're actually talking about alders here) are Angiosperms with flowers that look remarkably like cones.  The entire Betulaceae family evolved from an evolutionary bridge group of plants that maintained more ancestral gymnosperm-like characteristics in its pollen and ovule-producing structures.  So alders are modern, flowering plants that produce seeds in fruits, but they have flowers that look just like the cones from their evolutionary ancestors.


Alder flowers look just like cones!

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