Members of the Asteraceae (sunflower or aster) family have complex flowers. Each flower head (what we commonly call the “flower”) is actually composed of many flowers.
Special terms are used to describe the various Asteraceae flowers.
Ray flowers are pistillate (female) or sterile and bilateral, with a long, strap-like 3-lobed corolla (petals collectively).
Disc (or disk) flowers are usually radial and bisexual with a 5-lobed corolla and no strap-like portion.
Ligulate flowers are bisexual and bilateral with a 5-lobed strap-like corolla
These three flower types form four different types of Asteraceae flower heads.
Radiate flower heads have a center of disc flowers surrounded by a margin of ray flowers. An example of a radiate flower head is the pictured common madia (Madia elegans). Sunflowers are another example of radiate heads.
Discoid heads have all disc flowers. Yellow star thistle (Centaurea solstitalis) is a discoid head.
Ligulate heads consist entirely of ligulate flowers. The common dandelion has a ligulate head as does the pictured yellow salsify (Tragopogon dubius).
Disciform heads appear to be composed of all disc flowers. However, the disc flowers along the margin are functionally or morphologically differentiated from the inner disc flowers being pistillate with minute ligules. There are few example of flowers with this head type – mostly plants of the genus Gnaphalium (cudweeds).
In addition to being a large family, the Asteraceae are a most complex and interesting group.
The common madia and yellow salsify were photographed on our ranch near Lookout CA (Modoc County). Thankfully, since it is a noxious weed, we do not have yellow star thistle on our property. This yellow star thistle specimen was growing near Baum Lake (Shasta County CA).