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

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ARECACEAE - the palm family

Systematic position : Class: Monocotyledonae. Series: Calycinae. Family: Arecaceae. Arecaceae is one of the largest families in monocotyledons. It includes about 217 genera and more than 2,500 species. The members of this family are distributed throughout the tropical regions of the world. In India, it is represented by about 25 genera and more than 225 species.

ARECACEAE - the palm family

 

Systematic position

 

Class: Monocotyledonae

 

Series: Calycinae

 

Family: Arecaceae

 

General characters

 

Distribution

 

Arecaceae is one of the largest families in monocotyledons. It includes about 217 genera and more than 2,500 species. The members of this family are distributed throughout the tropical regions of the world. In India, it is represented by about 25 genera and more than 225 species.

 

Habit

 

Mostly unbranched trees with arborescent stem having prominent scars of leaf bases and a crown of large leaves (eg. Cocos nucifera) or shrubs eg. Nipa fruticans has no aerial stem and leaves arise directly from the underground rhizome.

 

Root

 

Fibrous and adventitious root system.

 

Stem

 

Mostly aerial, erect, unbranched and columnar having prominent scars of leaf bases. Stem is short and stumpy in Phoenix acaulis. Internodes are usually short.

 

Leaf

 

Exstipulate, petiolate, petiole long and very strong with sheathing leaf base, palmately compound (eg. Borassus flabellifer) and usually in terminal clusters. Phyllotaxy is usually alternate spiral but scattered in Calamus. Venation is pinnately parallel (eg. Cocos nucifera) or palmately parallel divergent (eg. Borassus flabellifer).

 

Inflorescence

 

Large, usually lateral arising from the axils of leaves, spadix (eg. Phoenix sylvestris) or compound spadix (eg. Cocos nucifera) enclosed by a large woody bract called spathe. In Corypha umbraculifera (Kudai panai), the spadix is terminal and it measures about 10 metres. It is a monocarpic plant. The plants are polycarpic and monoecious (eg. Cocos nucifera) or dioecious (eg. Borassus flabellifer).

 

Flower

 

Bracteate, ebracteolate, sessile, usually unisexual and monoecious or dioecious, trimerous, incomplete, actinomorphic and hypogynous. In Borassus flabellifer, the male flowers are smaller than female flowers. In Cocos nucifera male flowers are densely arranged at the upper portions of the spike and female flowers are at the base of the spike.

 

Perianth

 

Tepals 6 arranged in two whorls of three each, persistent, polyphyllous or gamophyllous showing valvate or twisted or imbricate aestivation. In Phoenix acaulis, the tepals of outer whorl are united and valvate while that of inner whorl are free and twisted.

 

Androecium

 

Stamens 6 arranged in two whorls of three each and opposite to tepals. Anthers are dithecous, basifixed or dorsifixed, introrse and dehiscing longitudinally. Pistillode is usually present in male flowers.

 

Gynoecium

 

Ovary superior, tricarpellary and syncarpous. Ovary trilocular with single ovule showing axile placentation. In Phoenix acaulis, the placentation is basal. Style extremely short or absent and stigma three. Staminode is present in female flowers. In Cocos nucifera, two carpels become abortive out of three.

 

Fruit

 

A drupe with fibrous mesocarp.

 

Seed

 

Seed with small embryo and abundant endosperm.

 

 

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