This is the largest family of the angiosperm and includes about 1528 genera and 22750 species.In Nepal, it represents 104 genera and 428 species.
The members of the family are found all over the world(cosmopolotian), most of them are found in the tropical regions.
2. Habit and Habitat:
Annual or perennial herbs or under shrubs or shrubs, rarely trees or climbers. Many are xerophytes or mesophytes, a few are aquatic.
Usually, tap and branched, sometimes adventitious. In Helianthus, the roots are modified into tubers.
Erect or postulate, rarely climbing, herbaceous or woody, solid or fistular, sometimes spiny e.g. Sonchus, sometimes modified into tuber e.g. Helianthus, some contains latex e.g. Sonchus or oil glands.
Radical, cauline or ramal, usually alternate, sometimes opposite and rarely whorled, simple or compound, estipulate, glabrous or hairy; entire or serrate or lobbed, apex acute or obtuse, reticulate venation.
Racemose, head or capitulum with an involucre of bracts; rarely in spike.
Sessible, bracteable or ebracteate, two kinds of flowers are found in inflorescence, towards the center are tubular flowers called disc florets and towards the periphery of captulum are liguate flowers called ray florets.
Ray florets: Sessile, bracteates or ebracteate, ireegular or zyomorphic, ligulate, incomplete, unisexual or neuter, pentamerous, epigynous.
- Calyx: Sepals-2-5, represented by scales or hairy, pappus, velvate, superior.
- Corolla: Petals-3, gamopetalous, ligulate, velsate superior.
- Androecium: Absent
- Gynoecium: Bicapellary, sycarpous, ovary inferior, unilocular containing a single anatropous ovule, basal placentation, style long and slender, stigma bifid.
Disc floret: Sessile, bracteate or ebracteate, actinnomoprphic, incomplete or complete, bisexual, pentamenous, tubular, epigynous.
- Calyx: Sepals-2-5, represented by scale or hairy peppus, aestiration, superior.
- Corolla: Petals-5, gamopetalous, tubular, actinomorphic, valvare aestivation, superior
- Androecium: Stamen-5, syngenesious epipetalous, anthers bicelled, basified, introse, supenor
- Gynoecium: As in ray floret i.e. bicapellary, syncarpous, ovary inferior, unilocular containing a single anatropous ovule, basal placentation, style long and slender, Stigma bifid.
- Fruit: Cypselu
- Seed: Exalbuminous
Family: Compositae (Asteraceae)
Economically important plants:
Helianthus annus (sunflower) : oil yielding
Tagetes patula (Mangold): medicinal plants
Lactuca satira (Lettuce): vegetable
Dahlia variabillis : ornamental
Diagnostic features of family Compositae (Asternaceae):
- Stem: hairy and with latex or oil ducts
- Inflorescene: head or capitulum having involucres of bract
- Flowers: Sessile called florets, two types of flowers ; ray florets and disc florets
- Florets: tubular or ligulate, epigynous
- Calyx: represented by sales, bristles or pappus
- Corolla: 3-5, gemopetalous, toothed
- Stamens: -5, syngenesioud and epipetalous in disc floret
- Gynociem: bicapilarry, ovary inferior, based placentation
- Fruit: Cypsela