When is a “petal” not a petal? When is a “flower” not a flower?

 

When is a “petal” not a petal? When is a “flower” not a flower? The answer to both of those questions is the same. Ponder if you will, then continue for the answer.

A “petal” is not a petal and a “flower” is not a flower when we’re dealing with a plant in the Asteraceae, the botanical family that’s known by various names, including the sunflower family, the daisy family, the aster family, and the composite family. Take the flower head of this bush sunflower, Simsia calva. Where I say flower head, most people would say flower, but the botanical truth is that you’re looking at two collections of small flowers that together make up a single flower head. All the tiny thingies (forgive that highly technical term) crowded into the center are individual flowers, and because they form a sort of disk they’re called disk flowers. The disk flowers around the edge of the disk in this bush sunflower have already opened, and the greener ones inside the ring are beginning to turn yellow and will open soon.

Radiating outward from that central disk is another whole set of different-looking individual flowers called ray flowers, of which there are 20 broad and sunny ones in this flower head. (Go ahead and count them, you’ll see.) Most people think those are the petals of a single flower, but now you know that that’s not the case, and you can understand why this family was traditionally called the composite family.

As if that weren’t complicated enough, I’ll add that while most members of the composite family have both disk flowers and ray flowers, some species have only ray flowers, some other species have only disk flowers (like the Texas thistle, of which you saw a bud last time), and there are some species in the composite family that begin with both kinds of flowers but soon shed their ray flowers. In some species the disk flowers are fertile but the ray flowers are not (as in the bush sunflower); in other species the ray flowers are fertile but the disk flowers are not; in still other species both sets of flowers are fertile.

Quite a few species in the Asteraceae produce flowers that don’t look like daisies or sunflowers (for example climbing hempvine, marsh fleabane, shrubby boneset, purple mistflower, and poverty weed). Enough already, you say? Hey, I’m only the messenger; that’s just the way things are in this huge, complex, and diverse botanical family, which is the one in central Texas that more species belong to than any other.

I took today’s photograph of a single bush sunflower flower head on June 13th along Great Northern Blvd., the only place I know for sure I can find this species.

© 2014 Steven Schwartzman

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