General Features Of The Asteraceae Family

The genus Artemisia is one of the largest and most widely distributed of the nearly 100 genera in the tribe Anthemideae of the Asteraceae (Compositae).

Asteraceae is a natural family, with well established limits and a basic uniformity of floral structure, represented in all its members by the common possession of characters such as aggregation of the flowers into capitula and production of achenes (cypselae) as the typical fruits of the family. The cypsela structure, the presence or not of a pappus, and the capitulum itself, that seems to have evolved in order to simulate an individual flower with respect to pollinator attraction, are all morphological features which have an adaptive significance and whose taxonomic value has been demonstrated in only a few groups such as the Anthemideae and the Cardueae (Heywood et al, 1977).

Asteraceae, in spite of their relatively uniform capitular and floral features, occupy a wide range of habitat types and are found in abundance on every continent except Antarctica.

On a global scale the family has ca. 23,000 species (Bremer 1994), almost 10% of the total Angiosperm flora of the world (Wilson 1986).

Ecological diversification must have begun very early in the development of the family and this ecological plasticity has been made possible largely through habitat diversification, which includes a wide range of forms, from highly reduced, small, montane annuals (less than 1 cm high) to relatively large tropical trees (up to 20 meters tall), most of which are soft-wooded. Slow-growing, cold-enduring, hard-wooded shrubs such as Artemisia occur along with fast-growing, cold-sensitive, herbaceous genera, over a wide range of latitudes.

The family is very distinctive in its chemical attributes; several classes of plant compounds are characteristic of this family, as we will describe later in this chapter. Many of these substances elaborated by the family are toxic or show other significant physiological activity. This may be one reason why plants of the Asteraceae are rarely used in human diets or for animal fodder, with few important exceptions such as lettuce (Lactuca sp.) and sunflower (Helianthus annuus), the latter being probably the most useful economic plant of the family (Heywood et al., 1977).

The rich accumulation of essential oils and other terpenoids in certain Asteraceae is responsible for the use of various members such as tansy (Tanacetum vulgare) and wormwood (Artemisia absinthium) for flavouring foods or liqueurs. Terpenoids and certain phenolic compounds are also responsible for the value of many species of Asteraceae in pharmacy and medicine (Wagner 1977).

The subdivision of the family into 13 tribes by Bentham (1873) has been largely accepted, and the basic classification of the family as recognised today is little different from the original one. Bentham's tribal classification has stood the test of time, and with some modifications such as those introduced by Hoffmann (1894), and by Dalla Torre and Harms in their Genera Siphonoganarum (1907) still form the basis of most current work (Heywood et al., 1977). More recent proposals for classification include the division of the family into two phyletic groups (Carlquist 1976), which often led to the creation of two or more subfamilies (Wagenitz 1976; Jeffrey 1978), and the recent classification of the Asteraceae according to Bremer (1994), in which the family is divided into 17 tribes split into two subfamilies (the Asteroideae and the Cichorioideae).

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