Bee on Coneflower Here’s how we’ve absorbed the basic model of a flower without even realizing it. Because we’re expecting to see sepals, petals, stamens and pistils, we get sunflowers and their kin totally wrong. (More on sepals vs. petals here.)

I remember being astounded when a friend of mine who was getting his degree in Biology at the time told me the things I was calling petals weren’t petals at all but individual flowers. “No kidding?” I said. “Those are the ray flowers,” he said, full of the enthusiasm of the late-in-life student. “And these things? Those are the disk flowers.” He pointed at what I’d always more or less assumed was stamens and pistils but hadn’t really looked at.

“Sunflowers have two sets of flowers. That’s why they call them composites.”

Thanks to him I started seeing sunflowers and the rest of the Family Asteraceae with new eyes – and taking flower structure a lot less for granted.  

Compositae is an older, still-used name for this the largest family of seed-bearing plants. It includes everything from asters to daisies, artichokes to lettuce and, of course, sunflowers.

When you’re talking Asteraceae, the proper term for all those “numerous separate flowers” (1) is a “head.” A head can consist of as many as a thousand florets, according to one source. (2)

A typical sunflower head consists of a whorl of ray flowers with “long, flat corollas” surrounding the “tubular, 5-toothed corollas” of the disk flowers. (3) I have some shots of Blanketflower (Gaillardia aristata) in my gallery that show what I mean.

On the outermost whorl of the head, where you’d expect to find sepals, there are “phyllaries” instead. These are a series of green bracts, (4) sometimes also called involucre bracts. Involucre derives from the Latin for envelop and involve, and in botany refers to “covering,” which is just the job for bracts.

To my eye, the bracts often form a sort of cup for the ray and disk flowers to sit in. There’s something about the structure, I guess, but it’s one of my favorite parts of so-called “true sunflowers,” like Helianthus annuus, the ever-present Kansas, or what my mother calls “roadside,” sunflowers. A wilder example is Helianthella quinquenervis, aka 5-nerved Sunflower.

In a plant family as large as the Asteraceae (500-plus species in the Rocky Mountain region alone), there is plenty of room for variation. Some members have only ray flowers, like dandelions. Some, only disk flowers, like thistles. In some the ray flowers are sterile and the disk flowers take care of reproduction –or vice versa. A mind-numbing number of composites are yellow and nicknamed DYFs for “damn yellow flowers” by flower buffs. But let us not overlook all the purples, blues, whites and violet hues of the genus Aster, Erigeron, Townsendia, Liatris and others.

Some composites are spring-blooming but “from mid-August until frost, the wildflower show is dominated by plants of this family,” notes Ruth Ashton Nelson. (4) In the last couple of years I’ve been surprised to see Black-eyed Susans (Rudbeckia hirta) popping up as early as late June, which I take to be an indication of a changing climate.

You gotta love a plant family that includes everything from weeds to the unassuming yet aptly named Pussytoes (Antennaria) to forest beauties like Heart-leaved Arnica (Arnica cordifolia). Take it from me, it’s worth taking a closer look at Sunflowers. You might discover a whole new world.

NOTES:

2 Guide to Rocky Mountain Plants, Ruth Ashton Nelson, revised by Roger L. Williams (1992)

1 https://www.britannica.com/plant/Asteraceae

3 Op. cit.

4 Ibid