Wednesday, 20 August 2008
FAMILY OF THE WEEK: LORANTHACEAE -- MISTLETOE FAMILY
Around 1300 species are observed throughout the world mostly distributed in tropical and temperate regions.In India the family is represented by 11 genera and 50 species mostly in western ghats and tropical and subtropical Himalayas.The familiar examples are Mistletoe (Viscum) and Banda (Dendropthe falcata)
The plants are mostly semiparasitic shrubs which derive a considerable part of nourishment from the host tree. They are attached to the host with the help of modified adventitious roots (haustoria) which penetrate the bark and sapwood of the host. They attack a wide range of trees.
The stem is sympodial and often dichotomous. In Viscum the terminal bud ends in an inflorescence whereas the lateral buds continue to grow in next season.The branches are often swollen at nodes.
The leaves are usually opposite,persistent,often thick and fleshy,simple and exstipulate.
Inflorescence and flowers:
The flowers are mostly in axillary spikes, racemes or cymes.
The flowers are often showy bisexual or unisexual, actinomorphic or with a tendancy to zygomorphy(Dendropthe) and epigynous.They are usually bracteate and often with a pair of bracteoles.
The perianth is often biseriate with two similar di or tri merous whorls. The tepals are free or united into a tube which often splits down to one side.
The stamens are many.The anthers are dithecous. A pistillode is often present in the staminate flowers and a staminode in female flowers.The gynoecium is bi or tri carpellary and syncarpous
The fruit is a berry or drupe.
Pollination is by insects or small birds.
The fruit is covered by the fleshy outer receptacle which has an outer viscid layer.This adheres to the beak of the birds. When the bird rubs the beak to get rid of the seeds they adhere to the branches of the new host where they germinate and soon develop haustoria which penetrates the tissues.
Posted by SATISFIED at 18:24