Not Done with Symmetry Yet

I enjoyed painting the bottom view of the dragon fruit (DF) yesterday. My watercolor sketch didn’t quite portray the type of spiral symmetry one sees quite clearly in the flower of a sunflower or a pineapple. In all honesty, the symmetry in the DF isn’t that clear. Perhaps I got a defective one.

Today’s study

When I bought the DF, I also purchased the pineapple and something called a ‘Star Fruit’. I never saw or heard of a star fruit before, but it looked interesting.  When I posed it for sketching, I was surprised to see that it was a five-sided star. Having been immersed in the hexagonal shapes of the pineapple and the hexagon-looking shapes of the scales on the DF, I must have been thinking, “Star fruit? Oh yes, the Star of David, a six-sided star.”

Here is the sketch:

Watercolor Sketch -Starfruit

Star Fruit
9″x12″ 140# Cold Pressed Watercolor Block

Before I talk about where a pentagonal shape fits into the whole plant symmetry issue, I’d like to say a few words about the sketch itself.

The colors are fairly accurate. I used thalo yellow green and lemon yellow for the planes of the fruit in the light. The edges of the fruit were nearly uniformly brown, so I used a mixture of yellow ocher and Van Dyke brown, with stronger (perhaps too strong) application on the lower front edge of the fruit. For the green in shadow, I cut the thalo yellow green with black.  I used latex mask for the reflective spots, which seemed to work except for the ones in the shadows. I need to tone them down so they don’t look like white spikes.

Plant symmetry

The first stop on my search for plant symmetry yielded two terms: zygomorphic and actinomorphic.  Zygomorphic refers to a flower with one plane of symmetry. In other words, bilaterally symmetric (like the anatomy of a human). Actinomorphic refers to a flower which is radially symmetric, or having several planes of symmetry. I illustrated this with the crude sketch below:

Pencil diagram of zygomorphic and actinomorphic symmetry in plants

Plant Symmetry Diagram 

Aha! The star fruit is bilaterally symmetric (if it is proper to apply flower parlance to the fruit). Actually I’m not at all sure this is correct. I have no idea about the mechanics of star fruit emergence. Is the spiral symmetry of a fruit (resulting from the stacking of the hexagons in the pineapple, for example) a consequence of the actinomorphic structure of its flower? I need to do more research to understand this.

Yesterday I speculated that there must be some kind of genetic basis for plant symmetry. While this is way over my head, from what I understood of an article by Wenhen Zhang, et al, floral zygomorphy evolved independently more than 38 times, but they investigated a gene called CYCLOIDEA2 that is responsible for symmetry in a diversity of plants belonging to a certain evolutionary branch.(Wenheng Zhang, Elena M. Kramer, and Charles C. Davis  Floral symmetry genes and the origin and maintenance of zygomorphy in a plant-pollinator mutualism   PNAS April 6, 2010 vol. 107 no. 14 6388-6393)

The rest is too complex for me, but I’m satisfied knowing that there is a gene somewhere at the bottom of all this.  I would like to know more about symmetry of fruit and its relation to the type of plant from which it springs.

8 thoughts on “Not Done with Symmetry Yet

  1. Hi Jack – lovely star fruit. I know that your particular interest at the moment is shape (symmetry) but what I was struck by was how well you had captured that waxy texture which a star fruit has. When I buy one I often hesitate to cut into it because of the almost unnatural shine and polish of the skin…

    • Thank you, Liz. I appreciate the feedback, because I was just trying to get the appropriate coloration. Apparently, the shading worked, and the colors. There was the brownish tinge to the edges as well. It’s nice to know that it worked. Thanks!

      How does one cut into a star fruit, anyway?



          • Oh dear. I never realised… Yes, the starfruit! Actually, not longitudinally but the other way, cutting across the points round the middle (what I thought of as horizontal). Do you know that there are stars inside some fruits? If you cut an apple around its middle rather than the more usual way you will find a star. The stars vary depending on the variety and other things but they are often quite beautiful. I’ve found stars in other similar fruits. The starfruit, however, is outside-in about its star. L

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