The order iscosmopolitan (plants found throughout most of the world including desert and frigid zones), and includes mostlyherbaceous species, although a small number of trees (such as theLobelia deckenii, the giant lobelia, andDendrosenecio, giant groundsels) andshrubs are also present.
Asterales are organisms that seem to have evolved from one commonancestor. Asterales share characteristics onmorphological and biochemical levels.Synapomorphies (a character that is shared by two or more groups through evolutionary development) include the presence in the plants ofoligosaccharideinulin, a nutrient storage molecule used instead ofstarch; and uniquestamen morphology. The stamens are usually found around thestyle, either aggregated densely or fused into a tube, probably anadaptation 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 name and order Asterales is botanically venerable, dating back to at least 1926 in theHutchinson system of plant taxonomy when it contained only five families, of which only two are retained in theAPG III classification. Under theCronquist system of taxonomic classification of flowering plants,Asteraceae was the only family in the group, but newer systems (such asAPG II and APG III) have expanded it to 11. In the classification system ofRolf Dahlgren the Asterales were in thesuperorder Asteriflorae (also called Asteranae).
The orderAsterales currently includes 11 families, the largest of which are the Asteraceae, with about 25,000 species, and theCampanulaceae (bellflowers), with about 2,000 species. The remaining families count together for less than 1500 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 11 families as more closely related to each other than to other plant families or orders such as therosids.
The phylogenetic tree according to APG III for the Campanulid clade is as below.[4]
Although most extant species of Asteraceae are herbaceous, the examination of the basal members in the family suggests that the common ancestor of the family was an arborescent plant, a tree or shrub, perhaps adapted to dry conditions, radiating from South America. Less can be said about the Asterales themselves with certainty, although since several families in Asterales contain trees, the ancestral member is most likely to have been a tree or shrub.
Because all clades are represented in the Southern Hemisphere but many not in the Northern Hemisphere, it is natural to conjecture that there is a common southern origin to them. Asterales belong toangiosperms or flowering plants, a clade that appeared about 140 million years ago.[citation needed] The Asterales order probably originated in theCretaceous (145 – 66Mya) on the supercontinentGondwana which broke up from 184 – 80 Mya, forming the area that is now Australia, South America, Africa, India and Antarctica.
Asterales contain about 14% ofeudicot diversity. From an analysis of relationships and diversities within the Asterales and with their superorders, estimates of the age of the beginning of the Asterales have been made, which range from 116 Mya to 82Mya.[4] However few fossils have been found, of theMenyanthaceae-Asteraceae clade in theOligocene, about 29 Mya.
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 (34 – 23 Mya) pollen is known for Asteraceae andGoodeniaceae, and seeds from Oligocene andMiocene (23 – 5.3 Mya) are known for Menyanthaceae and Campanulaceae respectively.[5] According tomolecular clock calculations, the lineage that led to Asterales split from other plants about 112 million years ago[6] or 94 million years ago.[7]
All Asterales families are represented in the Southern Hemisphere; however, Asteraceae and Campanulaceae are cosmopolitan and Menyanthaceae nearly so.[8]
The Asterales, by dint of being a super-set of the family Asteraceae, include some species grown for food, including thesunflower (Helianthus annuus),lettuce (Lactuca sativa) andchicory (Cichorium).[9] Many are also used as spices and traditional medicines.
Asterales are common plants and have many known uses. For example,pyrethrum (derived from Old World members of the genusChrysanthemum) is a natural insecticide with minimal environmental impact.[10]Wormwood, derived from a genus that includes thesagebrush, is used as a source of flavoring forabsinthe, a bitter classical liquor of European origin.[11]
W. S. Judd, C. S. Campbell, E. A. Kellogg, P. F. Stevens, M. J. Donoghue (2002).Plant Systematics: A Phylogenetic Approach, 2nd edition. pp. 476–486 (Asterales). Sinauer Associates, Sunderland, Massachusetts.ISBN0-87893-403-0.
Lindley, John (1833).Nixus plantarum (in Spanish). London: Apud Ridgway et Filios. Retrieved14 April 2020.
