Inflorescence an involucral head or capitulum with 1 to many florets on a receptacle surrounded by an involucre of bracts (phyllaries)
A head can contain:
1. Ligulate florets only - Ligulate head
2. Tubular florets only - Discoid head
3. Ray and tubular florets - Radiate head
Fruit is an achene
The Asteraceae is normally divided into 13 tribes. The major tribes and some major genera in those tribes are listed below:
1. Heliantheae - Helianthus (sunflower)
2. Asterae - Aster, Solidago (Goldenrod)
3. Senecionae - Senecio - contains around 1500 species
and is one of the largest angiosperm genera.
4. Eupatorieae - Eupatorium, Liatris
5. Cynareae - Carduus, Cirsium (thistles)
6. Lactuceae - Cichorium (chickory), Lactuca (Lettuce)
Economic importance:
Helianthus - sunflower seeds and oil
Lactuca - lettuce
Ambrosia - ragweed
Chrysanthemum (pyrethrum)
Many ornamentals
Diagnostic characteristics: infl. a head surrounded by bracts
Members of the Asteraceae are more commonly in flower in late Summer and Fall in temperate areas.
Genera are rather ill-defined, which can make the writing of efficient keys difficult
You should be able to identify the following structures: tube florets, ligulate florets, involucral bracts, chaffy bracts (pales), pappus bristles, receptacle. Chaffy bracts, scales or hairs are often present on receptacle
Iridoids are absent but many members of the Asteraceae produce sesquiterpene lactones and alkaloids, both of which are thought to function as feeding deterrents
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