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Asterales

(Order)

Overview

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The Asterales are an of dicotyledonous flowering plants which include the composite family Asteraceae (sunflowers, daisies, thistles etc.) and its related families.

The order is cosmopolitic, and includes mostly herbaceous species, although a small number of trees (Lobelia) and shrubs is also present.

The Asterales can be characterized on the morphological and molecular level. Synapomorphies include the oligosaccharide inulin as the nutrients storage, and the stamens are usually aggregated densely around the style or even are fused into a tube around it. The last property is probably associated with the plunger (or secondary) pollination, which is common among the families of the order.

Families

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The Asterales include about eleven families, the largest of which are Asteraceae, with about 25,000 species, and Campanulaceae, with about 2,000 species. The remaining families count together for less than 500 species. The two large families are cosmopolitic with center of mass in the northern hemisphere, and the smaller ones 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

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The Asterales order probably originated in the Cretaceous on the supercontinent Gondwana, in the area which 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

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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.

Photos

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Taxonomy

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The Order Asterales is further organized into finer groupings including:

Families

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Asteraceae

Annuals, biennials, perennials, subshrubs, shrubs, vines, or trees. Roots usually taproots, sometimes fibrous. Stems usually erect, sometimes prostrate to ascending (underground stems sometimes woody caudices or rhizomes, sometimes fleshy) . Leaves usually alternate or opposite, sometimes in basal rosettes, rarely in whorls; rarely stipulate, usually petiolate, sometimes sessile, sometimes with bases decurrent onto stems; blades usually simple (margins sometimes 1 2+ times pinnatifid or palmatifid), rarely compound. Inflorescences indeterminate heads (also called capitula) ; each head usually comprising a surrounding involucre of phyllaries (involucral bracts), a receptacle, and (1 ) 5 300+ florets; individual heads sessile or each borne on a peduncle; heads borne singly or in usually determinate, rarely indeterminate, arrays (cymiform, corymbiform, racemiform, spiciform, etc.) ; involucres sometimes subtended by calyculi (sing. calyculus) ; phyllaries borne in 1 5( 15+) series proximal to (i.e., outside of or abaxial to) the florets; receptacles usually flat to convex, sometimes conic or columnar, either paleate (bearing paleae or receptacular bracts that individually subtend some or all of the florets) or epaleate (lacking paleae) ; epaleate receptacles sometimes bristly or hairy or bearing subulate enations among the florets. Florets bisexual, pistillate, functionally staminate, or neuter (also called neutral) ; sepals highly modifed (instead of ordinary sepals, each ovary usually bears a pappus of bristles, awns, and/or scales, sometimes in combination within a single pappus) ; petals connate, corollas (3 ) 5-merous, ± actinomorphic or zygomorphic (one or both kinds in a single head, see descriptions of radiate, discoid, liguliflorous, disciform, and radiant following) ; stamens (4 ) 5, alternate with corolla lobes, filaments inserted on corollas, usually distinct, anthers introrse, usually connate and forming tubes around styles (rarely filaments connate and anthers distinct; e.g., Heliantheae, Ambrosiinae) ; ovaries inferior, 2-carpellate, and 1-locular with 1 basally attached, anatropous ovule; styles 1 in each bisexual, functionally staminate, or pistillate floret; each style usually ringed at base by a nectary, distally 2-branched with stigmatic papillae borne on adaxial face of each branch in 2 separate or contiguous lines or in 1 continuous band (styles usually not branched in functionally staminate florets), style branches apically truncate or appendaged beyond the stigmatic bands or lines, appendages usually papillate to hirsute distally on abaxial (or abaxial and adaxial) faces. Fruits (technically cypselae, historically called achenes) usually dry with relatively thick, tough pericarps, sometimes beaked (rostrate) and/or winged (alate), often dispersed with aid from pappi. Seeds 1 per fruit, exalbuminous; embryos straight.[1] [more]

At least 77,978 species and subspecies belong to the Family Asteraceae.

More info about the Family Asteraceae may be found here.

References

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Footnotes

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  1. Theodore M. Barkley, Luc Brouillet, John L. Strother "Asteraceae". in Flora of North America Vol. 19, 20 and 21 Page 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16, 70. Oxford University Press. Online at EFloras.org.

Sources

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Last Revised: November 19, 2008