Tuesday, May 26, 2015

Boojum Trees

Every time I go to Phoenix or Scottsdale, Arizona, I make a point of visiting the Desert Botanical Garden.

The landscape on display is entirely different from that of the Pacific Northwest, where I was raised, and I appreciate the range of unusual plants that flourish in the hot, dry climate of the Sonoran Desert.

But mostly I go to see the boojum trees.  There is a picture of one at the right in the picture above.  

The boojum is the most preposterous looking plant ever, rising in a tapered column from a slightly wider bottom to a slightly narrower top.  Unlike most trees, it has no branches, just small spiny pokeouts of the same size running its full length. 

Boojums look as if they were designed by Dr. Seuss.  They even have a funny common name, "boojum," derived from a fanciful passage in a Lewis Carroll book.  Boojum, boojum, boojum.  Hahahahaha.

Like other desert plants, the boojum adheres to the principle of photosynthesis.  It absorbs light, converts it to energy and uses the energy to grow.  With the addition of water, it generates oxygen in a virtuous cycle that sustains other organisms, including humans. 

Here is a traditional sketch of how photosynthesis works.

Plants in the desert, including the boojum, differ from this picture in several ways.  

First, they receive so much sunlight that leaves are less necessary and, in many cases, problematic.  Leaves that do exist tend to be lighter and smaller than those on plants in more moderate climes. (Darker leaves, like darker colors, absorb more heat and light from the sun; this is why most of your summer wardrobe is lighter colored and virtually all desert plants are light green.)

If a boojum tree had leaves like the one in the diagram above, they would shrivel between scarce rainstorms.  So the boojum holds its water supply in its funny-looking trunk.

Here is how photosynthesis works for a saguaro cactus, another plant much in evidence in the Sonoran Desert. 

A more detailed schematic would show the broad, shallow series of roots that capture water during each year's two brief rainy seasons.

Many of my friends enjoy posting animal videos on Facebook.  For me, it's boojum trees. I highly recommend a visit to see some in situ.

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