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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 List) and over 20,000 recognized species. Only the orchid family (Orchidaceae) is larger, with about 25,000 described species ^[1].

Contents

Description

Uses

Medical Importance

Footnotes

References

External links

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.


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 members of the Asteraceae are important as weeds, e.g., ragworts, groundsel, dandelions.

Medical Importance

Plants in Asteraceae are medically important in that the sesquiterpene lactone compounds contained within them are an important cause of allergic contact dermatitis. Allergy to these compounds is the leading cause of allergic contact dermatitis in florists in the US.^[2].

Footnotes

1. Introduction to assembling the Tree of Life: Orchidaceae
2. Andrews' Diseases of the Skin: Clinical Dermatology, , Richard B., Odom, W.B. Saunders Company, , ISBN 0721658326

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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