Compositae (Asteraceae)

What are the Compositae?

The Compositae (plants in the daisy or sunflower family) form one of the largest families of flowering plants with some 25,000 species (roughly 10% of the total number of flowering plants) in over 1,500 genera. It is one of the "core families" on which research at the Royal Botanic Gardens, Kew is concentrated.

The Compositae are instantly recognisable, through their compound inflorescences consisting of many tiny flowers: a daisy has a yellow "core" of 200 disc florets,surrounded by 50 marginal, white ray florets with a conspicuous limb. A single daisy "flower" contains about 250 separate flowers! A sunflower has basically the same format. A dandelion consists of one kind of florets ("ligulate") only, but still has many florets combining to look like a single flower. In the fruit stage, however, all the individual fruits are clearly visible, each with its own "parachute" (the so-called pappus).

The Compositae have a considerable ecological and economical importance. Members of the family occur from the polar regions to the tropics, and may range over all habitats from dry desert to swamp, and from rainforest to mountain peaks. In many regions of the world they comprise up to a tenth of the flora. The family contains some very large genera (Senecio with 1,250 species, Helichrysum (everlastings) with 600 species, Hieracium with 1000 species).

The Royal Botanic Gardens, Kew has a rich collection of living plants in the Gardens and the glasshouses, as well as one of the major collections of dry specimens in the herbarium (some half a million specimens).

Importance of Compositae

Weeds of agriculture

Many Compositae are noxious weeds: Sow Thistle (Sonchus), Thistles (Carduus, Cirsium), Black Jack (Bidens pilosa), poisonous Senecio species; Ragweed or Ambrosia pollen is the main cause of hay fever in the continental USA.

Food

Sunflower is one of the world's main oil crops; lettuce, endive, globe artichoke and chicory are some of the other food plants in the family. Examples of culinary herbs are tarragon and chamomile.

Medicine

In general, many Compositae are used as herbal medicines all over the world. In Europe, Arnica has been used for centuries in wound healing. In Africa, Vernonia amygdalina is used by both man and chimpanzee against intestinal parasites. In Mexico over 200 species of the family are used in folk medicine.

Insecticide

Powdered remains of Anthemideae have been found in the abdominal cavity of the mummy of Ramses II, probably as an insecticide. Inula species are called fleabane, because of their use. Pyrethrum, made from the fruit of Tanacetum cinerariifolium, is an excellent natural insecticide and can be used without harm to mammals.

Horticulture

Many Compositae are important garden ornamentals: Chrysanthemums, Crown daisies, Oxeye daisies, Marigolds, Cosmos, Aster, Goldenrod, Everlasting, Dahlia ...

Other uses

Although the family consists mainly of herbs or shrubs, some species grow to tree size and several of these are used for timber: in East Africa, Muhuhu (Brachylaena) is used as timber or as wood for woodcarving.

Research programmes

Floristic work is being carried out on Southern and Eastern Africa (Flora Zambesiaca, Flora of Tropical East Africa) and North-east Brazil (Flora of Bahia). Accounts for the Flore des Mascareignes (Indian Ocean) have also been published.

The work on the floras requires regional revisions of most of the genera treated. Further monographic work is carried on where required.

Economic botany: local uses are being collated and shared.

Collections

Compositae accessions can be found in several collections. There are many accessions, both in the gardens, the greenhouses, and the study collections. A vast amount of literature on the family is held in the Library; there are also Economic Botany collections and seed bank collections as well.