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BOTANY Higher Secondary Second Year - Textbooks Online

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1.3.4. ASTERACEAE – the sunflower family<br />

Systematic position<br />

Class: Dicotyledonae<br />

Sub-class: Gamopetalae<br />

Series: Inferae<br />

Order: Asterales<br />

Family: Asteraceae<br />

General characters<br />

Distribution<br />

Asteraceae is the largest family of flowering plants comprising about<br />

900 genera and more than 20,000 species. They are distributed throughout<br />

the world. In India, about 138 genera and about 708 species are reported.<br />

Habit<br />

Mostly annual or perennial herbs (eg. Eupatorium odoratum) or shrubs<br />

(eg. Senecio) or trees (eg. Vernonia arborea). Root and stem commonly<br />

contain oil ducts. Many species have colourless latex.<br />

Root<br />

Normally a branched tap root system. Root tubers are found in Dahlia<br />

coccinea.<br />

Stem<br />

Aerial, erect or prostrate or decumbent, tuberous (eg. Helianthus<br />

tuberosus) or sucker eg. Chrysanthemum indicum (Akrakaram) or runner<br />

(eg. Launaea pinnatifida).<br />

Leaf<br />

Simple, entire or pinnately or palmately lobed or compound, alternate<br />

(eg. Vernonia arborea) or opposite (eg. Tridax procumbens) or whorled<br />

(eg. Eupatorium odoratum) or radical (eg. Launaea pinnatifida), exstipulate<br />

showing reticulate venation, hairy (Tridax procumbens) and spinous (eg.<br />

Carthamus tinctorius).<br />

Inflorescence<br />

This family is characterized by the presence of head or capitulum type of<br />

inflorescence. The number of florets in a head is variable from a few to<br />

several hundreds, but in Echinops, the head is reduced to a single flower.<br />

35

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