Asteraceae: the sunflower family
The Aster family is huge (20,000 recognized species) and has enough variety to warrant the all-encompassing moniker ”DYCDamn Yellow Composite!“ when people start to learn plants.
Members of this family are often somewhat difficult to key, mainly because there are so many combinations of slightly-varying characteristics that don't readily present themselves to a casual observer. Indeed, you probably want a hand lens, possibly access to a dissecting scope. Splitting a flower in half reveals more about the shape of the calyx, the scales of the disk flowers, and appearances of parts on general. Aster family flowers are actually collections of smaller flowers that give the appearance of being one flower. These collections can be all disk flowers, all ligulate flowers, or most often a combination (this the old name Composites). Consider these examples:
Everyone knows what a sunflower looks like. They are the stereotypical flower shape people draw when they doodle: a daisy-like flower with a round center and radial petals; yet most people don’t realize what is going on with this common flower form: these are true composites: disk flowers make up the center, ray flowers surround that disk. When you start to look at your garden flowers, or flowers on your hikes, you will start to see just how many flowers are composites.
Everyone knows what a dandelion looks like. They are the common weed that home owners hate to see popping up in their lawn, yet most people don’t see what is really going on with this very common flower form: the entire flower head is made up of ligules: strap-like ray flowers only. This flower type is called ligulate. Think about the seed delivery systems of these flowers! A sunflower seed is quite unlike the familiar “parachute" of a ligulate flower, which uses wind to disperse the seeds.
Everyone knows what a thistle looks like. They are the common weed that people avoid due to the sharp leaves and spiny flower heads, yet most people don’t see what is really going on with this very common flower form: the flower head is made up of tubular disk flowers only. This flower type is called discoid, and it too is wind-delivered, so thistles develop fluffy seeds to float on the breeze, carrying the tiny hard achene (fruit) to new areas.
The Asteraceae family was once called Compositae
Because so many of the flowers in Asteraceae are composed of two types of individual flowers (ray flowers and disk flowers) the name Compositae was appropriate. As may be obvious, ray flowers are the petals that surround the central disk, which is composed of many individual disk flowers.
Visit Calphoto and see a list of 378 matching records from a search for Asteraceae in El Dorado County. Roll through a few pages of the names and photos and see how many ways this family can present these same three basic forms! This gives a glimpse of why Asteraceae are challenging to identify. Check this expansive family description:
Flowers bisexual, unisexual, or sterile, ± small, of several types; calyx 0 or modified into pappus of bristles, scales, or awns, which is generally persistent in fruit; corolla radial or bilateral (rarely 0), lobes generally (0)4–5; stamens 4–5, anthers generally fused into cylinder around style, often appendaged at tips, bases, or both, filaments generally free, generally attached to corolla near throat; pistil 1, ovary inferior, 1-chambered, 1-seeded, style 1, branches 2, generally hair-tufted at tip, stigmas 2, generally on inside of style branches.
There’s much going on that generally goes unnoticed until you get into taking the flower apart. The seeds of the disk flower should reveal either of two eventual methods of delivery; case and point, compare the sunflower seeds with the fluff of a dandelion. The former is spread by animals, the latter taken by the wind.
Then there’s the underside of the flower; where most other families have a specific number of sepals that are common to (nearly) all members of that particular family. In Asteraceae, there are many different kinds of sepals but they are called phyllaries. These phyllaries are often a distinctive characteristics used in the keying process.
Learning to key these flowers to species is more fun than most people initially think, and because it does take some dedication, many people steer away from trying. I personally think they are surprisingly interesting.
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