Asterales

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Asterales is an order of dicotyledonous flowering plants that includes the composite family (Asteraceae) and its related families.

The order is a cosmopolite, and includes mostly herbaceous species, although a small number of trees (such as some members of the genus Lobelia) and shrubs are also present.

The Asterales can be characterized on the morphological and molecular level. Synapomorphies include the oligosaccharide inulin, a nutrient storage molecule, 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 (or secondary) pollination that is common among the families of the order.

Contents

Families

The order Asterales includes about eleven families, the largest of which are the Asteraceae, with about 25,000 species, and the Campanulaceae, 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.

Under the Cronquist system, Asteraceae was the only family in the group, but newer systems (e. g. APG II) have expanded it.

Evolution and biogeography

The Asterales order probably originated in the Cretaceous on the supercontinent Gondwana, in the area that is now Australia and Asia. Although most extant species are herbaceous, the examination of the basal families in the order suggests that the common ancestor of the order was an arborescent plant.

Fossil evidence of the Asterales is rare and belongs to rather recent epochs, so the precise estimation of the order's age is quite difficult. An Oligocene pollen is known for Asteraceae and Goodeniaceae, and seeds from Oligocene and Miocene are known for Menyanthaceae and Campanulaceae respectively.

(Bremer and Gustafsson, 1997)

Economical importance

The Asteraceae include some species grown for food, including sunflower (Helianthus annuus), lettuce (Lactuca sativa) and chicory (Cichorium). Many spices and medicinal herbs are also present.

Of horticultural importance are the Asteraceae (e. g. chrysanthemum) and Campanulaceae.

References

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