ASTERACEAE (Compositae) - Sunflower or Aster Family

Herbs, shrubs, trees and vines (mostly herbs in temperate zones)

Leaves alternate, opposite or whorled, simple, no stipules

Flowers bi- or unisexual, actinomorphic or zygomorphic, referred to as florets

Two basic types of florets - Ligulate (ray) and Tubular (disc). There are variations on these two basic types, resulting in a total of five different types of florets:

1. Tubular (disc) - actinomorphic, perfect
2. Ray - zygomorphic, perfect, pistillate or sterile
3. Ligulate - zygomorphic, usually perfect

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

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. The sesquiterpene lactones can cause contact dermatitis. Members of the Asteraceae produce a wide array of toxic compounds, one of the most famous is Artemesia absinthium (wormwood), which produces thujone. Extracts of wormwood were mixed with alcohol to produce a drink called absinthe. This drink was popular in Europe for a time but has since been outlawed in most countries because of the toxicity of thujone. Vincent VanGogh supposedly consumed large quantities of absinthe and his insanity and genius have both been attributed to absinthe.

Medicinal uses - members of the Asteraceae have been used for a wide array of medicinal purposes. The one that has probably attracted the most interest recently is Echinacea purpurea (Purple coneflower), which produces compounds that stimulate the immune system.

Diagnostic characteristics: infl. a head surrounded by bracts

IMAGE GALLERY
FLOWERING PLANT GATEWAY (Asteraceae) (Compositae)