Portraits of Wildflowers

Perspectives on Nature Photography

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

with 32 comments


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.

Bush Sunflower Flower Head 2827

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


Written by Steve Schwartzman

July 3, 2014 at 6:00 AM

32 Responses

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  1. Very interesting, thank you 🙂 Love sunflowers. Over here in Cape Town, I also get confused with the bougainvillea – as to what is the actual flower, (apparently the tiny white thingies) and what Looks like the flower – the brightly coloured leaves!


    July 3, 2014 at 6:54 AM

    • You’re welcome. One of the most important things I learned when I got interested in native plants in 1999 was this information about the composition of flower heads in the sunflower family. I don’t know why it took me three years to get around to discussing it in this blog.

      You bring up another interesting point, the fact that in some species the actual flowers are less than what we think, rather than more. I explained that in a post last year, where I used snow-on-the-mountain as my example:


      It’s a coincidence that you mention Cape Town, because just the other night I saw part of a documentary about South Africa that singled out a relatively small region of the country and said it has more species of native flowers than all of Britain.

      Steve Schwartzman

      July 3, 2014 at 7:15 AM

      • Thanks for the link – very informative. And yes – The Cape does have unique flora, especially, I believe, Table Mountain, where some species are found no where else in the world.


        July 3, 2014 at 8:09 AM

        • Table Mountain: that rings a bell, and I believe it was the very area singled out in the television show. Let’s hope I get to see it in person one of these years.

          Steve Schwartzman

          July 3, 2014 at 8:17 AM

  2. The botanical world is just a tangled web of definitions waiting to be broken, odd paths into the nether regions of identification keys. 🙂 Don’t forget the flowers that Had both until some lovesick Romeo or Juliet happened by.

    Steve Gingold

    July 3, 2014 at 8:00 AM

    • I’d thought about the way those Juliets and Romeos pull “petals” off a daisy in the “he/she loves me, he/she loves me not” way. Isn’t it strange how people think the universe will accommodate their little divination schemes?

      Speaking of tangled webs of definitions and keys, I was looking at a botanical key when your comment arrived. I was puzzling over the description “oil several in the tubes indistinct, intervals.” Is there at least one typo in there, or am I supposed to make sense of that?

      Steve Schwartzman

      July 3, 2014 at 8:13 AM

      • What do I know? But I think it’s possible some words may have been scrambled, and some omitted. I found this in Asa Gray’s “Field, Forest and Garden Botany”: “Fruits mostly with oil-tubes in the form of lines or stripes, one or more in the intervals between the ribs, and some on the inner face, sometimes also under the ribs.” He goes on to catalog missing oil-tubes, pairs of oil-tubes, indistinct oil-tubes, multiple oil-tubes and so on. You can find it here.


        July 3, 2014 at 10:11 AM

        • I was puzzled by the seemingly garbled grammar and strange punctuation in what I quoted, more than by criteria relating to oil tubes, which I think I can follow if only they’re described clearly. I checked your link and, sure enough, it deals with plants in the parsley family, just like the plant in the key I was looking at. I was trying to find out how to tell Texas parsley from prairie parsley, and I learned that some botanists consider them to be two species while other botanists lump them into a single species.

          Steve Schwartzman

          July 3, 2014 at 10:26 AM

  3. Bracts?


    July 3, 2014 at 9:54 AM

  4. Great shot, Steve; I love the patterns, wheels within wheels!


    July 3, 2014 at 4:09 PM

    • Thanks, Lynne. Your “wheels within wheels” makes this one-time math teacher think of hypocycloids, even though there are none in this sunflower head.

      Steve Schwartzman

      July 3, 2014 at 4:37 PM

      • OK, Steve, I had to look that one up! Wikipedia does have a neat animation of hypocycloid so now at least I know what you’re talking about! I originally looked for a fibonacci pattern in the head but didn’t see it in this image – it seemed more concentric circle than cross spiral.


        July 3, 2014 at 4:41 PM

        • I agree that if there’s a Fibonacci pattern in this sunflower head it’s pretty well concealed. Even so, concentric is nice too, and a view of it can concentrate the mind.

          Steve Schwartzman

          July 3, 2014 at 4:53 PM

  5. thank you so much for the great lesson, ‘thingies’ and all! the image is stunning, and i really appreciated the refresher.. the next time that i paint a sunflower, i’ll be much more attentive to those details!

    happy fourth!


    • Especially the thingies, I’d say; a person can never get too many thingies. Happy attentiveness to details the next time you paint a sunflower, and happy Fourth mañana, when I’ll have a picture appropriately colored for the date.

      Steve Schwartzman

      July 3, 2014 at 10:52 PM

      • this sunflower painting was a group project, and the novice painters did very well:

        hmmm. a mescla of reds and blues? i’m thinking red salvia…here in the yard would be red hibiscus. and blue morning glories.. white? hmmm, white scorpion’s tail.. whatever you have on deck for the fourth of july post will be lovely and appropriate!

        on deck… when i was young, i was a barrel racer, and i always loved that call, ‘lisa and sunup starlett on deck…’ my horse was quite loca, and she flew around those barrels!

        • An excellent project: those sunflowers are appealing, and that’s a sundial like none I’d ever seen.

          Nice try, but you didn’t guess the components of my red-white-blue picture for the Fourth, which by now, after sunup, you may have seen already—provided you haven’t gone barreling off in another direction, young at heart as you are.

          Steve Schwartzman

          July 4, 2014 at 7:22 AM

  6. […] some resilient wildflowers have sprung back up. Here you see a sunflower (complete with its usual disk flowers and ray flowers) after the rain on the still-cloudy morning of June […]

  7. […] a refresher on disk flowers and ray flowers, you can look back at the text from a few days ago. If you’d like to, you can also take a glance at a Barbara’s buttons flower head in a […]

  8. Absolutely fascinating- how did I not know this??!! Thank you for this post- very interesting indeed!


    July 11, 2014 at 1:25 PM

    • You’re welcome, Martine. I learned this in 1999, when I first got interested in native plants, so for most of my life I didn’t know it either. Flowers of this type are so familiar to us all, yet we almost all misconstrue what we’re seeing. I think this topic should be part of science classes as early as elementary school, or by secondary school at the latest—but then I wish our schools taught (and held students accountable for!) so many things, including arithmetic, grammar, and geography.

      Steve Schwartzman

      July 11, 2014 at 1:44 PM

  9. […] Do you remember the great colony of basket-flowers that you saw last month? Now here’s a May 28th closeup taken during the same outing but a quarter-mile west at Meister Place in southernmost Round Rock. Today’s picture shows a Centaurea americana flower head as it was opening. People say that seeing is believing, but that’s not always so: despite differences in form and color, all the florets you see here are disk flowers; this species has no ray flowers. (For a refresher on disk flowers versus ray flowers, you can refer to a recent post.) […]

  10. […] ray flowers are yellow (in this case) while the disk flowers are black. Steve Schwartman’s nice discussion of these flower types will provide more […]

  11. […] * If you’d like a reminder of why the word flowers is in the plural here, you can have one. […]

  12. […] that everyone’s on board with ray flowers and disk flowers in plants of the sunflower family, here’s something strange I found on June 24th at the Floral Park Dr. entrance to Great Hills […]

  13. […] For an explanation (or reminder) of why today’s photograph shows dozens and dozens of flowers rather than just one, you can (re)visit a post from 2014. […]

  14. […] For any new readers who wonder why I keep saying say flower head when most people would say flower, you can find the explanation in a 2014 post with the quizzical title “When is a ‘petal’ not a petal? When is a ‘flower’ not a flower?” […]

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