Saturday, September 5, 2009

Sunflowers and the mysterious geometry of life

Where plants have five-fold patterns, a consideration of their souls is in place.
--Johannes Kepler

"Sunflowers (Helianthus annuus) are annual plants native to the Americas, that possess a large inflorescence (flowering head). Sunflower stems can grow as high as 3m (10 ft), and the flower head can reach 30 cm (11.8 in) in diameter with large edible seeds." (All quotations in this post except the one that begins it are from Wikipedia.) These sunflowers grew from birdseed, so I can't say exactly what kind they are, but here's a picture of how they look in the garden:

Everything about sunflowers is spiral-organized, from the swirl of leaves around the central stem, to the curved fanning-out of florets, petals, and sepals from the center of the flower, to the motion-sickness-inducing dip and sway of the whole plant in a breeze.

The seeds sprout early into robust little plants that are instantly identifiable, and in fact they're edible, too. Flower heads begin to form when the plant is about 1.5 feet high, but it will grow several more feet before they're perfected:

The sepals are intertwined at first, and separate so gracefully:

The flower begins to open:

It opens wider (growing larger all the time):

And wider, as the petals continue to form:

"The florets within the sunflower's cluster are arranged in a spiral pattern. Typically each floret is oriented toward the next by approximately the golden angle, 137.5°, producing a pattern of interconnecting spirals where the number of left spirals and the number of right spirals are successive Fibonacci numbers. Typically, there are 34 spirals in one direction and 55 in the other; on a very large sunflower there could be 89 in one direction and 144 in the other. This pattern produces the most efficient packing of seeds within the flower head."

For a marvellous explanation of the Fibonacci series, the golden mean, spirals, and, actually, life, the universe, and everything, seek out Michael S. Schneider's A Beginner's Guide to Constructing the Universe, and in particular Chapter Five (where I found the Kepler quotation that introduces this post).

What I've been calling the flower is "actually a head (formally composite flower) of numerous florets (small flowers) crowded together. The outer florets are the sterile ray florets and can be yellow, maroon, orange, or other colors. The florets inside the circular head are called disc florets, which mature into what are traditionally called "sunflower seeds," but are actually the fruit (an achene) of the plant."

The sterile ray florets:

The disc florets up close (with a critter):

Florets open for business:

Another beauty shot:

You can actually see sunflower pollen with your naked eye:

Sunflowers are home to, or are visited by, a wide variety of creatures. Click on this little cymid and you'll see it's liberally dotted with pollen:

I also lucked out and caught an image of this syrphid fly, which stayed still long enough for me to get a focus on the interesting "pleat" in its eyes: