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Chapter: 11 th 12th std standard Bio Botany plant tree Biology Higher secondary school College Notes

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DICOT FAMILIES : MALVACEAE - the cotton family

Systematic position Class: Dicotyledonae Sub-class: Polypetalae Series: Thalamiflorae Order: Malvales Family: Malvaceae

DICOT FAMILIES : MALVACEAE - the cotton family

 

Systematic position

 

Class: Dicotyledonae

 

Sub-class: Polypetalae

 

Series: Thalamiflorae

 

Order: Malvales

 

Family: Malvaceae

 

General characters

 

Distribution

 

This family includes about 82 genera and more than 1,500 species. The plants are cosmopolitan in distribution, more abundant in tropical and subtropical regions. In India, Malvaceae is represented by 22 genera and 125 species.

 

Habit

 

Plants may be annual herbs ( eg. Malva sylvestris) or perennial shrubs (eg. Hibiscus rosa-sinensis) or trees (eg. Thespesia populnea). The members of this family have mucilagenous substance. Stellate hairs occur on their young parts.

 

Root

 

Tap root system.

 

Stem

 

Aerial, erect (eg. Malva sylvestris), branched, woody (eg. Thespesia populnea), decumbent as in Malva rotundifolia (Thirikalamalli) and usually covered with stellate hairs.

 

Leaf

 

Petiolate, simple, entire (eg. Thespesia populnea) or palmately lobed

 

(eg. Gossypium arboreum), alternate, stipulate, margins usually toothed

 

(eg. Hibiscus rosa-sinensis) and showing reticulate venation.

 

Inflorescence

 

Solitary, terminal (eg. Malvastrum coromendelia) or solitary, axillary (eg.Thespesia populnea) or terminal or axillary cyme.eg.Pavonia odorata (Peramutti).

 

Flower

 

Bracteate or ebracteate, bracteolate or ebracteolate, pedicellate, dichlamydeous, pentamerous, complete, actinomorphic, regular, bisexual and hypogynous.

 

Epicalyx

 

Bracteoles forming a whorl outer to calyx is called epicalyx. Bracteoles 3 in Malva sylvestris, 5 to 8 in Hibiscus rosa-sinensis, 10 to 12 in Pavonia odorata and absent in Abutilon indicum.

 

Calyx

 

Sepals 5, green, gamosepalous showing valvate aestivation.

 

Corolla

 

Petals 5, coloured, polypetalous but slightly fused at the base due to adhesion with staminal tube, regular and showing twisted aestivation.

 

Androecium

 

Numerous stamens, filaments are fused to form a staminal tube around the style and monadelphous. The staminal tube is fused with the petals at their bases. Anthers are monothecous, reniform, transversely attached to filaments and transversely dehiscent.

 

Gynoecium

 

Ovary superior, two to many carpels but usually 5 to 10 carpels and syncarpous. Ovary with two to many locules. Pentacarpellary in Hibiscus rosa-sinensis, 10 in Althaea and 15 to 20 in Abutilon indicum. Number of locules usually corresponds to number of carpels. Each locule contains one to many ovules on axile placentation. Style long, slender and passes through the staminal tube ending in two to many distinct round stigmas.

 

Fruit

 

Loculicidal capsule e.g. Abelmoschus esculentus or schizocarp as in

 

Abutilon indicum and Sida cordifoliaI (Nilathuthi).

 

Seed

 

Endosperm is scanty, covered with hairs as in Gossypium barbadense.

 

 

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