Anthemideae Biological And Systematic Review

The Anthemideae is an important tribe in that it contains about 8% of the total genera and 13% of the species of the Asteraceae. The most distinctive characters of the tribe are the truncate-penicilliate styles with parallel stigmatic lines, the ecaudate or short-tailed anther appendages and the usually aromatic leaves (Heywood et al., 1977).

Generally, the place of origin of Angiosperms, and specifically that of the Asteraceae, are the Andean regions of northern South America or what was once western Gondwanaland (Raven and Axelrod 1974). The late Cretaceous or early Eocene is suggested to be the time of probable origin of the Asteraceae, at approximately the same date as the first upheaval of the Andes (Small 1919).

Of the thirteen tribes adopted, only two, the Asteroideae and the Senecioideae, may be said to be cosmopolitan or nearly so. The Cichorieae, the Cynaroideae and the Anthemideae belong to the northern hemisphere with chief centres in the Mediterranean and central Asiatic regions, and a few have spread over North America and even down the Andes to extra-tropical South America (Turner 1977). The Eurasian concentration of the tribe Anthemideae was largely due to their peripheral development in north-eastern Lauratia with respect to their Gondwanaland centre as a consequence of the phenomenon of continental drift.

The original Asteraceae were shrubby or woody plants, now they are mostly herbaceous as seen in the more largely herbaceous tribes of the Anthemideae and Cichorieae, in which many cases of secondary reversion to the woody condition have occurred. An example of this secondary reversion is represented by the genus Artemisia, as stated by Stebbins (1977), who refers to it as one of the most specialized genera of a relatively specialized tribe, the Anthemideae. This tribe has an intermediate percentage (39%) of woody or partly wooded genera, but the three genera (Hymenopappus, Hymenotbrix and Leucampyx) which link the Anthemideae to other tribes, particularly the largely herbaceous Helenieae, are all herbaceous. Furthermore, the anomalous stem anatomy observed in the shrubby species of

Artemisia would be expected in a secondary revertant from herbaceous forms (Diettert 1961; Moss 1940).

Geographical Patterns

The Anthemideae are essentially palaearctic in distribution and about 75% of the species occur in the northern hemisphere. They have many species and genera centred in middle Asia, South-West Asia, the western Mediterranean region and the Far East.

Some of the larger genera including Artemisia and Achillea are widely distributed in north temperate regions, but most genera have more discrete centres of distribution.

The 400 and more known species of Artemisia are mainly found in Asia, Europe and North America, but a few species occur in most temperate countries. They are mostly perennial herbs and shrubs dominating the vast steppe communities of Asia, the "sage-brush" communities of the New World and Karoo scrub of South Africa (Heywood and Humpries 1977). Koekemoer, (1996) has recently given a detailed account of the distribution of the Asteraceae in South Africa, stressing the huge distribution in this region of the family. Fifteen of the 17 tribes recognized by Bremer (1994) are present, accounting for a total of 24,731 taxa, among which the Anthemideae with 270 species (12%) and 35 genera, 60% of which are endemic, comprise a large component of southern African flora (Koekemoer 1996 and refs. cited therein) (Table 1).

Floral Biology

There are two pollination modes in the Anthemideae, anemophily (wind pollination) in Artemisia and in its immediate allies (Ainswort Davis 1908) such as Crossostephium, and entomophily (insect pollination) occurring in the remaining genera.

A number of pollen studies have been conducted in the Anthemideae, using both light and electron microscopy, and many of these studies have been concerned with the characterization and identification of Artemisia pollen (Skvarla et al., 1977). Stix, (1960) recognized two basic pollen types in the Anthemideae, Anthemis and Artemisia, distinguishing them by spine presence in the former and absence or great reduction in the latter.

Floral modification characteristic of anemophilous species include inconspicuous often pendulous capitula and florets, loss of nectar production and dry spineless pollen, in contrast with the sticky spiny pollens of the entomophilous genera (Skvarla and Larson 1965).

Some other important features of Artemisia spp. pollen anatomical structure, such as the complex and interwoven branches of the basal grain columellae and the reduced grain dimensions, have been investigated by Vezey et al. (1993) and discussed at the tribal level.

Table 1 Number of Asteraceae species per tribe in the world (Bremer 1994) and in South Africa (Arnold 1994) (extracted from Koekemoer 1996).

No. of species % of species in No. of species in % of species Tribe in the world the world South Africa in South Africa

Subfamily: Cichorioideae

No. of species % of species in No. of species in % of species Tribe in the world the world South Africa in South Africa

Subfamily: Cichorioideae

Mutisiae

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