Asteraceae

? Sunflowers
Aster alpinus
Plant Info
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Asterales Family: Asteraceae Martynov, 1820
Diversity
About 1500 genera and 23,000 species
Subfamilies
Barnadesioideae Cichorioideae Tribe Arctotidae Tribe Cardueae Tribe Eremothamneae Tribe Lactuceae Tribe Liabeae Tribe Mutisieae Tribe Tarchonantheae Tribe Vernonieae Asteroideae Tribe Anthemideae Tribe Astereae Tribe Calenduleae Tribe Eupatorieae Tribe Gnaphalieae Tribe Helenieae Tribe Heliantheae Tribe Inuleae Tribe Plucheae Tribe Senecioneae Tribe Tageteae See also List of Asteraceae genera
Synonyms
Compositae Giseke

The family Asteraceae or, alternatively, Compositae, known as the aster, daisy or sunflower family, is a taxon of dicotyledonous flowering plants. The family name is derived from the genus Aster and refers to the star-shaped flower head of its members, epitomized well by the daisy. The Asteraceae is the second largest family in the Division Magnoliophyta, with some 1,100 genera (see the List_of_Asteraceae_genera) and over 20,000 recognized species. Only the orchid family (Orchidaceae) is larger, with about 25,000 described species .

Description

Plants belonging to the Asteraceae share all the following characteristics (Judd et al., 1999). None of these traits, taken separately, can be considered synapomorphic.

• The inflorescence is an involucrate capitulum (flower head)
• Tubular/disc florets are actinomorphic, ligulate/ray florets are zygomorphic
• Anthers are syngenesious, i.e. with the stamens fused together at their edges, forming a tube
• The ovary has basal arrangement of the ovules
• One ovule per ovary
• The calyx (sepals) of the florets are modified to form a pappus, a tuft of hairs, which often appears on the mature fruit
• The fruit is an achene
• In the essential oils Sesquiterpenes are present, but iridoids are lacking.

A typical Asteraceae flower head (here Bidens torta) showing the individual flowers

Flowers of a sunflower with different forms and phases (sterile ray flowers, disc flowers in female, male and unopened phases)

The most common characteristic of all these plants is an inflorescence or flower head; a densely packed cluster of many small, individual flowers, usually called florets (meaning "small flowers").

Plants in the family Asteraceae typically have one or both of two kinds of florets. The outer perimeter of a flower head like that of a sunflower is composed of florets possessing a long strap-like petal, termed a ligule; these are the ray florets. The inner portion of the flower head (or disc) is composed of small flowers with tubular corollas; these are the disc florets. The composition of asteraceous inflorescences varies from all ray flowers (like dandelions, genus Taraxacum) to all disc flowers (like pineapple weeds).

The composite nature of the inflorescences of these plants led early taxonomists to call this family the Compositae. Although the rules governing naming conventions for plant families state that the name should come from the type genus, in this case Aster and thus Asteraceae. However, the long prevailing name Compositae is also authorized as an alternative family name (ICBN Art. 18.6).

The numerous genera are divided into about 13 tribes. Only one of these, Lactuceae, is considered distinct enough to be a subfamily (subfamily Cichorioideae); the remainder, which are mostly overlapping, are put in the subfamily Asteroideae (Wagner, Herbst, and Sohmer, 1990).

Uses

Commercially important plants in the Asteraceae include the food crops lettuce, chicory, globe artichoke, sunflower, yacón, safflower and Jerusalem artichoke. Guayule is a source of hypoallergenic latex.

Many members of Asteraceae are copious nectar producers and are useful for evaluating pollinator populations during their bloom. Centaurea (knapweed), Helianthus annuus (domestic sunflower), and some species of Solidago (goldenrod) are major "honey plants" for beekeepers. Solidago produces relatively high protein pollen, which helps honey bees overwinter.

Many members of the family are grown as ornamental plants for their flowers, e.g., chrysanthemums and some are important ornamental crops for the cut flower industry. Some Asteraceae are economically important in the sense that they are considered noxious weeds, e.g., dandelions.

Ray floret : A = ovary; B = pappus; C = theca; D = ligule; E = style with stigma

Disc floret : A = ovary; B = tube of corolla with teeth of the corolla; C = theca; D = style with stigma

Footnote

Helichrysum petiolare

References

• ITIS report 2002-09-10
• International Code of Botanical Nomenclature (ICBN, St. Louis Code). 1999. website (Published as Regnum Vegetabile 138. Koeltz Scientific Books, Königstein. ISBN 3-904144-22-7)
• Walters, Dirk R. and David J. Keil (1996). Vascular plant taxonomy. 4th ed. Kendall/Hunt Publishing Company. Dubuque, Iowa.
• Wagner,W.L., D.R. Herbst, and S.H. Sohmer. 1990. Manual of the Flowering Plants of Hawai‘i, Vol. I. University of Hawaii Press, Honolulu. 988 pp.
• Judd, W.S., C.S. Campbell, E.A. Kellogg, and P.F. Stevens. 1999. Plant Systematics: A Phylogenetic Approach. Sinauer Associates, Sunderland, MA.
• D. J. N. Hind, C. Jeffrey & G. V. Pope (eds.), Advances in Compositae systematics. - Royal Bot. Gardens, Kew, 469 pp., 1995

External links

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