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The Science of Flower Development….Doesn’t It Ruin the Aesthetic Beauty of Flowers?

I’m aware of no better answer to such a question than this one from Richard Feynman:

OK, now back to flower development, in general, and daffodils, in particular.…

About The Daffodil’s “Trumpet”

A report recently published online in The Plant Journal (please see Ref. 1 below) addresses questions about the nature of the daffodil flower. Although only a summary of this article is currently available online (unless you subscribe to this scientific journal), I’ve been able read the full text (so that you don’t have to). Here’s my take on this story.

8479482887 032d74d56c bMaybe we should start by taking a closer look at the flower of the daffodil.

Starting from the outside working in, the six petals are actually “tepals”, which are a kind of developmental combination of sepals and petals.

Next up is the famous trumpet-shaped part of the daffodil flower called the corona (“crown”) that is the main subject of this blog post.

The central part of the daffodil flower consists of the six stamens that encircle the carpel (gynoecium). In the photo (right), you can barely see the anthers (produce pollen) of the stamens, and also you can only see the top of the carpel called the stigma (receives pollen).

When And How Is A Daffodil Flower Made?

You maybe surprised to find out that a small version of the daffodil flower actually develops not in the spring just before it blooms, but at the end of the previous growth season. Thus, a floral bud is fully formed, and over-winters, within the dormant bulb.

This meant that the plant scientists investigating daffodil flower formation (see Ref. 1 below) had to dissect out flower buds from the developing bulbs. Whew!

As a result of these efforts they discovered that the daffodil corona forms relatively late in the flower-development program.

As described in a previous post, the flower-development program can be described like a play with several acts.

376px One daffodil bulbIn the first act, the plant genetically shifts from a vegetative state to a flowering state. In the second stage, which I call “arranging the chairs”, the spatial arrangement of the flower is determined. In the third act, which I call “seating the guests”, the different flower parts (in this case, tepals, stamens and carpel) are seated in their appropriate “chairs”.

In daffodils (and perhaps other species within the Amaryllis plant family that have trumpet-shaped flowers) there apparently is a fourth act. In this final act of daffodil flower development, new “chairs” are provided and arranged in a circle between the rings of the tepals and the stamens. The “late” guests are then seated. The question was: to which of the four basic flower parts (sepals, petals, stamens, carpels) are these “late” guests related? Turns out they are genetically related to stamens.

But, of course, an obvious question is: how does the daffodil make something that looks like petals by starting with the genetic “blueprints” for stamens?

The honest answer is we simply don’t know at the present time. It should be mentioned, however, that some of the results of Ref. 1 show that there is a late burst of coronal growth in the spring, so a great deal of elaboration of the “stamen” program is happening to result in a petal-like structure. This and other evidence suggest that petal-like structures “…can be produced by different genetic pathways even within the same flower.” (from Ref 1 below)

Why The Trumpet-Shaped Flower?

Most explanations from botanists involve attracting pollinators. But who pollinates domesticated daffodils? Mostly likely, it’s people!

Most of the showy daffodils that we see in the spring in parks and around homes and businesses are a product of plant breeding, i.e., artificial selection, not natural selection. (You can read more about this here.)

That is, such daffodil flowers are a product of what has looked good to humans (daffodil breeders especially), not insects. Indeed, most of the domesticated daffodils that we see in the spring may not be especially attractive to bees, and thus the daffodils may not even be pollinated (unless the bees are desperate).

What about the origin and evolution of trumpet-shaped flowers (before humans got involved)?

No one can be absolutely certain of an answer, but the long narrow corona of the genus Narcissus may have evolved to accommodate pollination by bees over butterflies or moths, which can’t easily enter the tall narrow corona to access the pollen. (from Ref. 2 below)

393px Michelangelo Merisi da Caravaggio Narcissus WGA04109In Summary:

If all of the above was a bit much, it might help to listen to a brief (4 min) audio clip about the daffodil’s mysterious trumpet courtesy of The Science Show on Australian Broadcasting Corporation’s RadioNational.

OK, if you’ve listened to this audio clip, then you’ve heard that the “trumpet” or “corona” of the daffodil flower is probably not an extension of the petals, as previously thought, but is a distinct organ – sharing genetic identity with stamens.

If you haven’t listened (and even if you have), you can read brief summaries of Ref. 1 below here and here.

References

1. Waters, M. T., A. M. M. Tiley, E. M. Kramer, A. W. Meerow, J. A. Langdale, and R. W. Scotland (2013) “The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls.” The Plant Journal, article first published online: 13 MAR 2013 (Abstract)

2. Graham, S. W. and S. C. H. Barrett (2004) “Phylogenetic reconstruction of the evolution of styler polymorphisms in Narcissus (Amaryllidaceae).” American Journal of Botany, Vol. 91, pp. 1007–1021. (PDF)

Photo Attributions:

Daffodil flower – JKehoe_Photos

Daffodil bulb – By Dvortygirl (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Painting of Narcissus – Caravaggio [Public domain], via Wikimedia Commons

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