An Exemplary Member of Asteraceae

Cutleaf Rosinweed

Cutleaf Rosinweed

I love this photograph of a cutleaf rosinweed blossom.  As a nature photographer, I’m not an artist – I’m a reporter.  The art is God’s business- “Nature is the art of God” (Dante.)  My hope is that my photographs attractively portray God’s art.  Initially I liked this photograph because it attractively portrays the beauty of a lovely bright yellow flower.  But since I’ve been using it as my computer display background for about a month now and staring at it daily, I’ve also come to appreciate it for something else…

The plant family Asteraceae is huge with over 15,000 species.  You’ll see them blooming from early spring –

Early Asteraceae - Philadelphia Fleabane

Fleabane

 fleabanes, for example – on through the fall season.  The white and blue asters are about the only prolifically blooming wildflowers still blooming here in north Georgia right now.  While there are many exceptions, most plants in this family have blossoms with bright “petals” and a contrasting central disk.  Think black-eyed susan, daisy, and sunflower.  Oh, and rosinweed.

Until only a couple of years ago, I didn’t realize the intricasy of the ‘standard’ blossom of those flowers.  It was only when I started to photograph and (try) to identify wildflowers that I learned what is clearly demonstrated in this article’s introductory photo – there’s more to a blossom than just a glance reveals.   The blossom of members of the Asteraceae family are really made up of multiple small flowers – florets.  They are either disk flowers (that central part of the blossom,) ray flowers (what we usually think are petals,) or, as in the case of the “classic” aster family members, both.   Let’s take a closer look at our rosinweed blossom.

Rosinweed disk florets

Rosinweed disk florets

This cluster of central disk florets clearly show their flower structure – corolla tube, petal-like lobes, and the stamens rising above the disk.  If this were a sunflower, those central disk flowers would have a pistil, since the seeds develop from the disk flowers.  In rosinweed, however, the seeds develop from the ray flowers.  Take a look at the photo below.

Rosinweed Ray Florets

Ray Florets

If you look closely at the base of the ray flowers (“petals”) you can see the pistil and what I think are rudimentary, sterile filaments rising out of the corolla tube of these florets.  These will receive the pollen from, I think, the stamens on the disk florets, and will develop the seeds of the plant. 

By the way, this is a moderately rare member of the aster family.  Silphium pinnatifidum is found only in a relatively narrow geographic band of 7 states from Georgia and Alabama up to Wisconsin.  It was once classified as Silphium chickamaugense, named for an area of Walker County, Georgia in which I live. 

I really like that cutleaf rosinweed blossom…

 

References:

Wildflowers of Tennessee by Jack B. Carman

USDA Plants Database

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