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Principles of Botany

Compositae

by Pat Calie

Fields of Study

Botany; Entomology; Evolutionary Biology; Paleobotany

Abstract

The Compositae family consists of more than eleven hundred genera worldwide and possibly as many as twenty-three thousand species. Representatives of the family are found on every continent except Antarctica. Species diversity is high in the southwestern United States and Mexico, in southern Brazil and along the South American Andes Mountain range, along the Mediterranean region, in Southwest and Central Asia, in South Africa, and in Australia.

Key Concepts

  • inflorescence: the flower head of a plant; in the Compositae family this typically consists of several small flowering bracts growing in a single group from the same point at the top of the main stem

  • polyacetylenes: carbon-based compounds whose molecular structure can be derived from the polymerization of smaller compounds containing the highly reactive carbon-carbon triple bond

  • sesquiterpene lactones: cyclic organic compounds of fifteen carbon atoms in which a carboxylic acid function (−COOH) has reacted with an alcohol function (−OH) in the same molecule to form the cyclic ester linkage that characterizes a lactone

A Big, Colorful Family

The Compositae family, generally termed the “composite flowers,” consists of more than 1,100 genera worldwide and possibly as many as 23,000 species. Representatives of the family are found on every continent except Antarctica. Species diversity is high in the southwestern United States and Mexico, in southern Brazil and along the South American Andes Mountain range, along the Mediterranean region, in Southwest and Central Asia, in South Africa, and in Australia.

Inflorescence

At first glance, the flowering head of many Compositae, such as that of the sunflower, resembles a single large flower with what appears to be a set of petals surrounding a cluster of anthers and stamens. Upon closer inspection, this compound inflorescence, or capitulum, is really a collection of highly reduced and modified flowers borne on a flowering stalk (peduncle). The expanded and flattened top of the peduncle is the receptacle and is surrounded by a series of leaf-like structures termed bracts that collectively comprise the involucre.

Two types of reduced flowers can be present within a capitulum, either ray or disc flowers, or both. The ray flower superficially resembles a petal and occupies the outer circumference of the capitulum. It can be either pistillate or sterile. The corolla is fused at the base, gradually expanding in width and eventually tapering to a tip. At maturity the tip of the ray flower corolla is oriented away from the center of the capitulum. The inner disc flowers can be either perfect (all reproductive parts present) or functionally staminate and possessing a corolla tube consisting of fused petals. At maturity the anthers and the stigmas will protrude from the corolla tubes. At the base of the corolla tube is a set of modified sepals termed the pappus. The pappus can consist of fine hairs, scales, or bristles, or it may be absent in some species. The seed is an achene and upon maturity is wind-dispersed with the assistance of the pappus.

A row of endives at a market (photo courtesy of Dinkum)

POBotany_p0087_1.jpg

Pollination Biology

A variety of mechanisms account for successful pollination in the Compositae, wind pollination being a very common mode. “Hay fever,” which in humans is an allergic reaction to plant pollen and other allergens, is greatly exacerbated in the late summer and early fall by the wind-pollinated ragweed (Ambrosia). Although often falsely accused, the goldenrods (Solidago) are not a major cause of hay fever, as they are pollinated by insects, not wind. By far, the majority of the species in the family are pollinated by insects, which are often attracted to the inflorescences by brightly colored ray flowers. The insect-pollinated flowers are typically generalists, attracting a variety of insects rather than a specific insect species. In some tropical taxa, birds or other animals are largely responsible for pollen exchange.

Economic Uses

Genera that contain species used for human consumption include endive and chicory (Cichorium), artichoke (Cynara), sunflower seeds and oil (Helianthus), lettuce (Lactuca), and dandelion greens (Taraxacum). Pyrethrum is a naturally occurring pesticide obtained from tansy (Tanacetum). Numerous genera are used as ornamental plants, such as marigolds (Calendula), Zinnia, bandana daisy (Gaillardia), and Dahlia. A number of plants are used for medicinal purposes. Coneflower (Echinacea) and fireweed (Liatris) are often used as herbal teas. Extracts from species of the Compositae are available from many health food retailers and practitioners of folk medicine. A current focus of pharmacological research is in determining those plant compounds responsible for producing beneficial effects in humans. Some species, however, contain compounds that at sufficient levels are quite toxic to animals, such as humans and livestock.

Evolutionary Success

Current opinion is that the family probably originated in South America or in the Pacific region, perhaps as early as the Tertiary period. Several reasons have been proposed for the biological success of the family. First, the pappus is a very efficient agent for wind-borne dispersal of mature seeds, serving as a lofting device (similar to a parachute) to carry the small seeds on air currents over great distances. Second, the agents of pollination are diverse, ranging from mechanical (wind) to biological (insect or bird). Third, many members of the family exhibit unique chemical compounds (such as sesquiterpene lactones and polyacetylenes) that may discourage large herbivores and insects from foraging on the leaves, thus allowing plants to mature and engage in reproduction. It is the successful production of viable offspring that constitutes the major measure of evolutionary success in the family.

Further Reading

1 

Bremer, K. Asteraceae: Cladistics and Classification. Timber Press, 1994.

2 

Evans, J., ed. Ultimate Visual Dictionary. Dorling-Kindersley, 1998.

3 

Judd, W. S., C. S. Campbell, E. A. Kellogg, and P. F. Stevens. Plant Systematics: A Phylogenetic Approach. Sinauer Associates, 1999.

4 

Moore, R., W. D. Clark, and D. S. Vodopich. Botany. 2nd ed., WCB/McGraw-Hill, 1998.

5 

Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. Biology of Plants. 6th ed., W. H. Freeman/Worth, 1999.

Citation Types

Type
Format
MLA 9th
Calie, Pat. "Compositae." Principles of Botany, edited by Richard M. Renneboog, Salem Press, 2020. Salem Online, online.salempress.com/articleDetails.do?articleName=POBotany_0042.
APA 7th
Calie, P. (2020). Compositae. In R. M. Renneboog (Ed.), Principles of Botany. Salem Press. online.salempress.com.
CMOS 17th
Calie, Pat. "Compositae." Edited by Richard M. Renneboog. Principles of Botany. Hackensack: Salem Press, 2020. Accessed December 14, 2025. online.salempress.com.