Compositae: Characters and Affinity | Dicotyledons | Botany

In this article we will discuss about:- 1. General Characters of Compositae (Asteraceae) 2. Floral Formula of Compositae (Asteraceae) 3. Number and Distribution 4. Common Plants 5. Affinity and Economic Importance. 

General Characters of Compositae (Asteraceae):

Plants—usually herbs, sometimes shrubs (e.g., Eupatorium). Leaves—alternate (sometimes opposite), simple or variously lobed, exsti­pulate. Inflorescence—capitulum (excepting Caesulia, Layascea and Echinops), homogamous (e.g., Launaea, Emilia, Vernonia, etc.) or heterogamous, surrounded by an involucre of bracts.

Florets of the capitulum—sessile, bisexual or unisexual, or the outer (ray-florets) female or neuter, palaeated or non-palaeated. Sepals—absent or modified into pappus. Petals—(5), tubular, ligulate or bilabiate, valvate. Stamens—5, syngenesious, epipetalous. Carpels—(2); ovary inferior, 1-celled with one ascending, anatropous ovule borne on basal placenta; stigma bifid. Fruit—cypsella, often crowned by persistent pappus. Seed—exalbuminous. Embryo—straight.

Floral Formula of Compositae (Asteraceae):

Number and Distribution of Compositae (Asteraceae):

This family consists of about 950 genera and probably 20,000 species which are cosmopolitan.  

Common Plants of Compositae (Asteraceae):

(1) Sunflower (Helianthus annuus L.).

(2) Marigold (Tagetes patula L.).

(3) Chrysanthemum (Chrysanthemum coronarium L.).

(4) Garden zinnia (Zinnia elegans. Z. pauciflora L.).

(5) Lettuce (Lactuca sativa L.), used as a salad.

(6) Enhydra fluctuans Lour., commonly found in marshes, used as a vegetable and reputed to induce sleep.

(7) Jerusalem artichoke (Helianthus tuberosus L.), cultivated for its tubers.

(8) Niger seed (Guizotia abyssinica Cass.) yields an oil much used for adulterating purpose.

(9) Safflower (Carthamus tinctorius L.), cultivated in cold weather for the orange dye from the petals and for oil from the seeds.

(10) Climbing hemp weed (Mikania scandens Willd.), a climber.

(11) Tridax procumbens L., very common in grassy waste lands and old walls, bearing cream-coloured flower-heads on long stalks during the dry season.

(12) Blumea lacera DC., a very common annual weed with yellow flowers.  

(13) Iron weed (Vernonia cineria Less.), another common weed with purplish flowers.

(14) Vernonia anthelmentica Willd., a medicinal plant.

(15) Eclipta alba Hassk. = E. prostrata L., also a common weed, the juice of the leaves of which is used in tattooing.

(16) Eupatorium ayapana Vent., a medi­cinal plant, the leaves of which are reputed as a specific for stopping internal haemorrhage; E. odoratum L., a common weed.

(17) Wedelia calendulacea Less., a medicinal plant, the leaves of which are used for promoting the growth of hair.

(18) Adenostemma viscosum DC., a common weed.

(19) Ageratum conyzoides L., Elephant’s foot (Elephantopus scaber L.), E. spicatus L., Milk-thistle (Sonchus oleraceus L.), S. asper Vill., Sphaeranthus indicus L., Cnicus arvensis Hoffm. and Emilia sonchifolia DC. are common weeds.

(20) Senecio nudicaulis Ham., Caesulia axillaris Roxb. and Crepis japonica Benth., are common in the rice-fields.

(21) Dahlia, Cosmos, Daisy, Aster, Calendula, Gallardia are common garden plants.

(22) Grangea maderaspatana Poir., generally found on roadsides, dry fields and waste places.

(23) Gnaphalium indicum L. and G. luteoalbum L., commonly found in dry fields.

(24) Common cockle-bur (Xanthium strumarium L.) occurs everywhere.  

(25) Synedrella nodiflora Gaertn., occurs in cultivated fields and waste places.

(26) Spilanthes acmella Murr. occasionally found.

(27) Silybum marianum Gaertn., occurs in gardens.

(28) Launaea asplenifolia DC., and L. pinnatifida Cass. = L. cermentora Alston., very common weeds in grassy glades and open fields..

(29) Ethulia conyzoides L., an erect annual herb.

(30) Erigeron asteroides Roxb., another common weed.

(31) Sagebrush (Artemisia caruifolia Ham.), a soft-stemmed plant, 2-4 ft. high.

(32) Echinops echinatus Roxb., a branched annual, 1-2 ft. high, not common.

(33) Cichorium intybus L., an erect herb.

(34) Centrotherum anthelmenticum O. Kuntze., a common tall robust annual.

(35) Sigesbeckia orientalis L., a very common weed on the hills.

Affinity and Economic Importance of Compositae (Asteraceae):

Compositae has been regarded as the highest evolved family of dicotyledons by many taxonomists. Its similarity with the members of Rubiales, such as, Dipsaceae and Valerianaceae, is very remark­able. The notable features of similarity between Rubiaceae and Compositae are the aggregation of flowers into head or head-like structure and in the reduction of calyx-lobes.  

If the polyphyletic origin is taken into consideration, then it may be assumed that the origin of Rubiales and Compositae commenced from Umbelliferae, which exhibits a tendency towards aggregation of small flowers in crowded umbels.

Compositae, however, can be readily recog­nized by capitulum inflorescence with an involucre, presence of pappus, gamopetalous corolla (tubular or ligulate or both), synge­nesious stamens, 1-celled inferior ovary with a single basal ovule, and cypsella fruit.

The reasons for treating compositae as the highest evolved family are given below:

(1) The dominance of herbaceous habit.

(2) Presence of large number of species and their cosmopolitan distribution.

(3) The remarkable adaptation for cross-pollination by insects in the following:

(a) Easily accessible nectar and its protection from mechanical injury, such as, rain, cold, etc.

(b) Crowding of florets in capitula with ligulate marginal florets which act as flag for the attraction of insects.

(c) All the disc florets can be pollinated by a single insect within a very short time.

(4) The presence of syngenesious protandrous stamens along with epigyny are considered as one of the advanced characters.

(5) The capacity of the florets to avoid self-pollination by brush­ing system (piston mechanism) along with the mechanism in the stigmas for the same purpose is undoubtedly the most advanced character of this family.

(6) The reduction of calyx and the number of carpels, solitary ovule with inferior ovary, and the protection of tender florets are taken as the highly evolved characters of this family. The reduced calyx (pappus) serve as parachute mechanism for the distribution of fruits and seeds; this is also considered as one of the advanced characters.

Economic Importance of Compositae (Asteraceae):

This family is of economic importance to a great extent. Some plants are used as food for man, such as lettuce (Lactuca), artichoke (Helianthus tuberosus), endive (Cichorium), salisfy (Tragopogon), etc. A kind of orange dye is obtained from safflower (Carthamus tinctorius); the dried petals are adulterated with saffron. Eupatorium, Calendula, Wedelia, Vernonia, Eclipta and Sausseria lappa are used in medicine.

Oil is extracted from Guizotia and Carthamus. Several species of the genus Artemisia (A. cina, A. vulgaris, A. maritima var. stechmaniana) yield ‘santonin’ of medicine. Pyrethrum is obtained from Chrysan­themum, cinerariefolium. Some plants are ornamentals, such as Asters, Chrysanthemum, Cosmos, Dahlia, Calendula, Gallardia, Sunflower (Helian­thus), Tagetes, Zinnia, Senecio, Echinops, etc.