Annual, biennial or perennial herbs, sometimes shrubs, rarely trees, with or without milky latex, sometimes armed with spines. Leaves alternate, opposite or rosulate, exstipulate, entire, toothed, lobed or variously dissected. Individual flowers (florets) usually small and numerous, sessile and aggregated on a receptacle, surrounded by an involucre made up of 1-several series of bracts (phyllaries or involucral bracts) and the whole structure forming a capitulum. Phyllaries may be herbaceous, fully scarious or at the margins only or chartaceous, usually with a sclerified portion in the centre (sterome) which may be undivided or divided into two parallel parts. Receptacle naked (epaleate) or bearing scales (paleate) or long hairs or bristles and receptacular surface with or without scale like ridges. Capitula with all florets of one sexual state, either male, female or hermaphrodite (homogamous) and heterogamous when florets of more than one sexual state are present. Homogamous capitula may be discoid or ligulate. Heterogamous capitula are radiate, radiant or disciform. Florets epigynous, bisexual, female or male (at least functionally) or sterile (neuter). Calyx often represented by a pappus of 1 or more series of bristles or scales on the apex of the ovary or sometimes pappus completely absent. Corolla gamopetalous, tubular, filiform, ligulate or rarely bilabiate, usually 3 or 5-toothed, rarely absent. Stamens 5, epipetalous, anthers connate forming a tube round the style, filaments free, rarely anthers free, dehiscence introrse, calcarate or ecalcarate, caudate or ecaudate or sometimes sagittate, endothecial tissues polar or radial; filaments usually with a collar. Ovary inferior, 1-celled. Style usually divided above into two branches with acute or obtuse sweeping hairs reaching below the furcation or not. Fruit cypsela, with or without ribs, sometimes with distinct carpopodium (basal attachment area).
Asteraceae, the largest family of Angiosperms, comprises of ± 1535 genera and c. 23000 species distributed in 3 subfamilies and 17 tribes. The number of genera is rather increasing as more than 10 genera are described each year and several are resurrected from or reduced to synonymy (Bremer, K. 1994. Asteraceae-Cladistics & Classification, Timber Press, Portland, Oregon). It is also the largest plant family in Pakistan, represented by over 650 species distributed in 15 tribes. In view of its massive size it has been decided to publish it in parts covering one or more tribes. Few genera which are not assigned to any tribe are tentatively placed in the nearest tribe. Such cases are marked with an asterisk. The account of three tribes Gnaphalieae, Inuleae and Plucheeae shall be published in the next fascicle of Asteraceae which will also include a complete generic key of all the taxa found in Pakistan. The circumscription of the tribes given below follows the treatment of Bremer (1994). We understand that the placement of the genera in different tribes is not final as our knowledge about this largest and important family is far from complete. As the new evidences are being gathered, there is every possibility of reshuffling of some of the genera from one tribe to the other and even few more new tribes may be erected from time to time.