Asterales (AST-er-ALE'-eez) is an order of dicotyledonous flowering plants that includes the large family Asteraceae (or Compositae) known for composite flowers made of florets, and ten families related to the Asteraceae.
The order is a cosmopolite (plants found throughout most of the world including desert and frigid zones), and includes mostly herbaceous species, although a small number of trees (such as the giant Lobelia and the giant Senecio) and shrubs are also present.
Asterales are organisms that seem to have evolved from one common ancestor. Asterales share characteristics on morphological and biochemical levels. Synapomorphies (a character that is shared by two or more groups through evolutionary development) include the presence in the plants of oligosaccharide inulin, a nutrient storage molecule used instead of starch; and unique stamen morphology. The stamens are usually found around the style, either aggregated densely or fused into a tube, probably an adaptation in association with the plunger (brush; or secondary) pollination that is common among the families of the order, wherein pollen is collected and stored on the length of the pistil.
The order Asterales currently includes eleven families, the largest of which are the Asteraceae, with about 25,000 species, and the Campanulaceae ("Bellflowers"), with about 2,000 species. The remaining families count together for less than 500 species. The two large families are cosmopolitan, with many of their species found in the northern hemisphere, and the smaller families are usually confined to Australia and the adjacent areas, or sometimes South America.
Only the Asteraceae have composite flower heads; the other families do not, but share other characteristics such as storage of inulin that define the eleven families as more closely related to each other than to other plant families or orders such as the Rosids.
