Southwest Desert Flora

Asteraceae or Compositae Family
Aster, Daisy, Composite and Sunflower Family

The Asteraceae or Compositae are commonly known by several names including Aster, Daisy, Composite and Sunflower Family. This family was described in 1792 by Paul Dietrich Giseke. The Asteraceae is one of the largest flowering families with a worldwide distribution except for Antarctica but the family is far more diverse in the tropical and subtropical regions of North America, the Andes, eastern Brazil, southern Africa, the Mediterranean region, central Asia, and southwestern China. Depending of the source, the Asteraceae are second in size only to the Orchidaceae. Some confusion is because it is very difficult to know with any certainty how many species are in each family.

There are many species in this large family they are broken down into 13 sub-families each with their own key characteristics. According to The Plant List there are 1,911 genera and 32,913 accepted species names for the family Compositae (=Asteraceae) and a further 32,205 scientific plant names of infraspecific rank. In North America there are 483 genera, 2,400 species and another 4,890 accepted taxa overall.

Asteraceae species have a capitulum (head) containing "florets" which are surrounded by involucre bracts or phyllaries. The type genus is Aster which is the reason for one of the common names of the family. The original family name, Compositae is a reference to the composition of "florets" on the head which in total make up the complete visible "flower".

Leaves may be simple occasionally compound, alternate, opposite, less commonly whorled, not infrequently they are opposite toward the base of the stems and alternate above, most leaves have petioles but some are sessile; and the plants often grow in basal rosettes, many are erect and others are prostrate or ascending; fruit is a one-seeded achene.

The individual species are mostly annuals, biennial or perennial; others are shrubs, vines or trees. Members of this family have major economic and ecologic significance.

Species in the Asteraceae family are economically important as specimens for horticultural (garden) and agricultural (food) purposes, others are noxious weeds and yet others are used for medicinal purposes.