In this article we will discuss about:- 1. General Features of the Compositae 2. Floral Range in the Compositae 3. Divisions 4. Position and Affinity 5. Number and Distribution 6. Commonly Occurring Plants 7. Economic Aspects.
General Features of the Compositae:
Habit – Herbs or shrubs.
Leaves – Alternate or opposite, simple, exstipulate.
Inflorescence – Head, surrounded by an involucre of bracts.
Flowers – All regular (tubular) or all irregular (ligulate) or both (forming disc and ray florets), epigynous.
Calyx – Absent or reduced to a tuft or hairs (pappus) or scales.
Corolla – Petals 4 or 5, united, tubular.
Androecium – Stamens 4 or 5, epipetalous, syngenesious; anthers 2-celled; connective prolonged upwards.
Gynoecium – Carpels 2, syncarpous; ovary inferior, unilocular with a single basal ovule’, style bifid at top and recurved.
Fruit – Cypsela, crowned with a persistent pappus.
Floral Range in the Compositae:
The peduncle is generally convex or flat. It is elongated and cane-like in Rudbeckia and Spilanthes. It is concave and cup-like in Epaltes.
The head is 1-flowered in Vernonia uniflora or few flowered in Mikania or many flowered in a number of other genera. It may contain one type of tubular and perfect florets. But the central florets are sterile in Schoenia. Unisexual florets are present in Xanthium. All florets in a head may be ligulate (Cichorium, Lactuca) or may have a bilabiate corolla (Mutisia).
Divisions of the Compositae:
The Compositae is divided into two subfamilies, one with a single tribe and the other with 12 tribes:
Subfamily I. Lactucoideae:
Latex present. Corolla of all florets ligulate.
Tribe (i) Cichoriecie:
Examples- Cichorium, Crepis, Lactuca, etc.
Subfamily II. Asteroideae:
Latex rare. Corolla of all disc florets not ligulate.
Tribe (i) Anthemideae:
Plants aromatic. Heads heterogamous, rarely homogamous. Receptacle chaffy or not chaffy. Anthers blunt or acute, not tailed, basifixed. Pappus absent or reduced to a ring or cup. Examples- Achillea, Artemisia, Chrysanthemum, etc.
Tribe (ii) Arctotideae:
Plants aromatic. Heads heterogamous. Anthers blunt pointed at base. Pappus none or not capillary. Examples- Arctotis and Gazania.
Tribe (iii) Astereae:
Plants aromatic. Heads heterogamous, rarely homogamous. Receptacle not chaffy. Anthers blunt and basifixed. Pappus various. Examples- Aster, Erigeron, Solidago, etc.
Tribe (iv) Calenduleae:
Plants not aromatic. Heads heterogamous. Receptacle not chaffy.
Anthers pointed at base. Pappus none. Example- Calendula.
Tribe (v) Cynareae:
Plants not aromatic. Heads homogamous, but rays may be female or neuter.
Receptacle chaffy, with many bristles. Anthers usually tailed. Pappus usually capillary. Examples: Carthamus, Cirsium, Saussurea, etc.
Tribe (vi) Eupatorieae:
Plants not aromatic. Heads homogamous. Anthers blunt and basifixed. Pappus 5 to many bristles or scales or none. Examples- Ageratum, Eupatorium, etc.
Tribe (vii) Helenieae:
Plants not aromatic. Heads heterogamous, rarely homogamous. Receptacle not chaffy. Anthers acute or blunt, not tailed, basifixed. Pappus not capillary, usually 2-3 awns or scales. Examples- Gaillardia and Helenia.
Tribe (viii) Heliantheae:
Plants not aromatic. Heads heterogamous, rarely homogamous.
Receptacle chaffy. Pappus not capillary, usually 2-3 awns or scales. Examples- Helianthus, Dahlia, etc.
Plants not aromatic. Heads homogamous or heterogamous. Receptacle chaffy or not chaffy. Anthers tailed. Pappus usually simple or plumose bristles. Examples- Blumea, Gnaphalium, Inula, etc.
Plants not aromatic. Heads homogamous or heterogamous. Anthers long tailed. Pappus capillary. Examples- Gerbera and Mutisia.
Plants not aromatic. Heads homogamous or heterogamous. Receptacle usually not chaffy. Anthers acute or blunt, not tailed, basifixed. Pappus capillary. Examples- Doronicum, Senecio, etc.
Plants not aromatic. Heads homogamous. Anthers blunt, sagittate or short tailed. Pappus seiose and copious. Examples- Elephantopus and Vernonia.
Position and Affinity of the Compositae:
The Compositae was the last family of the dicotyledons by Engler and was included in the order Campanulatae under the Metachlamydeae. Bentham-Hooker placed the family in the cohort Asterales under the series Inferae of the subclass Gamopetalae. In Hutchinson’s arrangement, the Compositae appeared under the Asterales. All these authors are in agreement to assign the position of the family after the Rubiaceae.
The Compositae has been thought to be at or very near the peak of dicot evolution. It indicates similarity with the Dipsacaceae and Valerianaceae. It is akin to the Rubiaceae in the aggregation of flowers into heads or heads-like structures and in the reduction of calyx lobes. If the polyphyletic origin of the Compositae is taken into account, the origin of the Rubiales and Asterales is to be sought in the Umbellales where the small flowers tend to aggregate into crowded umbels.
The available chemical data suggest that the Umbelliferae and Campanulaceae are the extant families closest to the ancestors of the Compositae. Though over 90% of more than 600 known sesquiterpene lactones belong to the Compositae, nine taxa of the Umbelliferae contain structurally simple types—guaianolides.
A second connecting link between the two families is the presence of many biogenetically related acetylenes. Like the sesquiterpene lactones, more than 90 % of the known acetylenes are from the two families. The Campanulaceae can be connected to the Compositae by its acetylenic chemistry and the Araliaceae and Pittosporaceae to the Umbelliferae.
The Calyceraceac, allied by some workers with the Compositae, chemically does not belong to the family. While the Calyceraceae lacks acetylenes, it contains secoiridoids similar to those occurring in the Gentianales; such compounds are completely absent from the Umbelliferae, Campanulaceae and Compositae.
In view of the various plausible relationships, Stebbins (1977) concluded that “the Compositae cannot be regarded as descended from or closely related to any other modern family”. As a matter of fact, this is implied in the cytochrome c data of Boulter et al. (1972). Such an aspect is also consistent with the fossil history of the group.
The Compositae is considered as the most advanced family of the flowering plants.
The reasons are as follows:
1. The preponderance of herbaceous habit, the number of shrub or tree members being exceedingly limited.
2. The presence of about 25,000 species or roughly about 10 percent of the known dicotyledonous plants which are cosmopolitan, being found, often in abundance, all over the world.
3. The admirable adaptation for cross pollination by insects, easy access to nectar and protection of nectar from the elemental forces of Nature; the aggregation of florets into heads with ligulate marginal florets, acting as flags for the attraction of insects; the pollination of all disc florets by one single insect within a very short time.
4. The occurrence of epigynous flowers in conjunction with the syngenesious and protandrous stamens.
5. The ability of florets to shirk self-pollination by brushing system or piston mechanism, together with the same procedure in the stigmas.
6. The protection of tender florets, suppression of calyx, reduction in carpel number and presence of an inferior uniovulate ovary.
7. The pappus forming a parachute for the dispersal of fruits and seeds.
Number and Distribution of the Compositae:
The Compositae is the largest family of flowering plants, comprising about 1,100 genera and 25,000 species. The members of this family are found in all corners of the globe, being poorly represented in the tropical rain forests and absent only from the Antartic main land.
Commonly Occurring Plants of the Compositae:
Adenostemma lavenia (L.) 0. Kuntze, Ageratum conyzoides L., Blumea mollis (L.) Druce, Cciesulia axillaris Roxb., Cirsium arvense (L.) Scop., Eclipta prostrata (L.) L., Elephant’s foot (Elephantopus scaber (L.), Emelia sonchifolia (L.) DC., Erigeron asteroides Roxb., Eupatorium odoratum L., Launaea asplenifolia Hook, f., L. sarmentosa (Willd.) Alston, Senecio nudicaulis Buch-Ham. ex D. Don, Sonchus asper (L.) Hill., Sphaeranthus indicus L.. Spilanthes paniculata Wall, ex DC., Synedrella nodiflora (L.) Gaertn., Tridax procumbens L., Vernonia cinerea (L.) Less., Cocklebur (Xantliium strumarium L.) and Youngia japonica (L.) DC. are weeds.
Sage Brush (Artemisia caruifolia Roxb.) is a soft stemmed plant, about a metre or so in height.
Centratherum anthelminticum (L.) O. Kuntze is a tall robust annual.
Chrysanthemum (Chrysanthemum coronarium L.), Sunflower (Helianthus annuus L.), Silybum marianum (L.) Gaertn., Marigold (Tagetes erecta L.) and Garden Zinnia (Zinnia elegans Jacq.) are garden plants.
Echinops echinatus Roxb. is a branched annual.
Enhydra fluctuans Lour, occurs in marshes.
Ethulia conyzoides L. f. is an erect annual herb.
Gnaphalium indicum L., G. luteo-album L. and Grangea maderaspatana (L.) Poir. are found in dry rice fields.
Climbing Hempwood [Mikania cordata (Burm.) B. L. Robinson] is a climber, bearing cordate leaves.
Economic Aspects of the Compositae:
The Compositae is of economic importance, “but for its size the importance is not as great as might be expected”.
The family contains a number of drug plants. Artemisia absinthium is used as an aromatic tonic. A. cina, A. maritima and A. nilagarica yield Pantonine’, used for expelling worms. The roots of Doronicum roylei are used as an aromatic tonic. Matricaria chamomilla (Mediterranean) is the source of ‘chamomile’, a medicine.
Other medicinal plants include Anthemis nobilis, Arnica montana, Calendula officinalis, Cnicus benedictus, Filago germanica, Petasites hybridus, Tanacetum vulgare, Vernonia anthelmintica, Wedelia calendulacea, etc.
There are many food plants in the Compositae. The leaves of Artemisia dracunculus are used for flavouring. Cichorium endivia (North America), Cynara cardunculus and Lactuca sativa are grown for lible leaves; Cynara scolymus for edible heads; Helianthus tuberosum for edible tubers; Scolymus hispanicus (Spain), Scorzonera hispanica (Europe to Central Asia) and Tragopogon porrifolius (South Europe) for edible roots. The roots of Cichorium intybus yield ‘chicory’ which is used to adulterate coffee. Enhydra fluctuans is eaten as a pot herb.
The members of the family find uses in a variety of ways. Adenostemma tinctorium produces a colouring matter. Brachylaena huillensis and Montanoa quadrangularis (Colombia & Venezuela) as well as some species of Vernonia furnish timber. Camphor is distilled from B. balsamifera (China).
A type of red dye is extracted from the flowers of Carthamus tinctorius. Oil is obtained from the seeds of C. oxyacantha, Guizotia abyssinica and Helianthus annuus. The flowers of Chrysanthemum carneum, C. cinerariaefolium and C. roseum are used to make insect powder.
The leaf juice of Eclipta prostrata is used for tattooing the skin bluish-black. Rubber is derived from Parthenium argentatum, Solidago leavenworthii and Taraxacum kok-saghyz. The roots of Saussurea lappa yield ‘pachuk’ of commerce, useful in perfumery, especially for the hair. The wood of Tarchonanthus camphoratus (South Africa) is used for musical instruments.
“A paging through a seed catalogue or a visit to a florist shop will show members of this family in their full grandeur”. Aster, Chrysanthemum, Cosmos, Dahlia, Gaillardia, Onopordon, Tagetes, Zinnia and many others are such representatives of the Compositae. Helichrysum arenarium and H. bracteatum are raised for their dried flowers.
Several members of the Compositae have become noxious weeds far removed from their original homes, e.g., Ageratum conyzoides, Bidens pilosa, Chondrilla juncea, Cirsium arvanse, Parthenium hysterophorus, Sonchus oleraceus, Tridax procumbens, Xanthium strumarium etc.
The species of Senecio are troublesome weeds of pasture and are responsible for deaths of domestic stock. The wind-borne pollen grains of Ambrosia artemisifolia and A. trifida are one of the chief causes of hay fever in the areas of North America where these species are prevalent.