EUPHORBIACEAE - the castor family

EUPHORBIACEAE - the castor family

Systematic position

Class: Dicotyledonae

Sub-class: Monochlamydeae

Series: Unisexuales

Family: Euphorbiaceae

General characters

Distribution

Euphorbiaceae includes more than 300 genera and about 7,500 species. It is world wide in distribution, but particularly well represented in Africa and South America. In India, it is represented by more than 70 genera and about 450 species.

Habit

This family includes a large number of annual herbs (eg. Phyllanthus amarus) or shrubs (eg. Ricinus communis) or trees (eg. Phyllanthus emblica). In several species of Euphorbia, the stem is modified to perform photosynthesis. This modified stem is called cladode and it resembles cactus. eg. E. tirucalli and E. antiquorum (Sadhurakkalli). This family shows a great range of variation in vegetative and floral characters. Almost all the plants have latex which is either milky or watery.

Root

A branched tap root system.

Stem

Aerial, erect or prostrate (eg. E. prostrata), cylindrical, branched, solid or hollow (eg. Ricinus communis), usually contains milky latex (eg.

E. tirucalli) or watery latex (eg. Jatropha curcas).

Leaf

Stipulate or exstipulate, petiolate, alternate (eg. Ricinus communis), simple, entire or deeply lobed or trifoliately compound (eg. Hevea brasiliensis) and with unicostate or multicostate reticulate venation. The stipules are modified into a pair of spines (eg. E.splendens) or glandular hairs (eg. Jatropha curcas). In xerophytic species of Euphorbia, leaves are reduced or absent. The leaves around the cyathium become beautifully coloured in E. pulcherrima (Paalperukki tree).

Inflorescence

The characteristic inflorescence of Euphorbia is cyathium. It is a collection of unisexual flowers arranged in cymose manner on a condensed axis and enclosed within a cup-shaped involucre. Each cyathium has a single central female flower surrounded by two to many male flowers. Each male flower is represented by a single stamen. They are arranged in centrifugal manner. The pedicel in female flower is short or long. If it is short, the female flower remains hidden within the involucre. If it is long, the female flower comes out of involucre. Extra floral nectar secreting gland is also located in the cyathium.

Various types of inflorescence are seen in the members of Euphorbiaceae. In Ricinus communis, it is a panicle where female and male flowers are arranged in racemose manner. Female flowers are at the top and male flowers below. In Croton sparsiflorus (Eli amanakku), the inflorescence is simple raceme, whereas in Acalypha indica (Kuppaimeni), it is catkin. In Phyllanthus amarus, the male and female flowers are axillary and solitary.

Flower

Bracteate, ebracteolate, pedicellate, unisexual, monoecious or dioecious, incomplete and hypogynous. In Euphorbia , the male flower is represented by a single stamen and female flower by a single pistil.

Perianth

In Croton sparsiflorus, the male flowers have two whorls of perianth whereas the female flowers have a single whorl of perianth. The male and female flowers of Euphorbia are usually devoid of perianth i.e aphyllous. The tepals are polyphyllous in Phyllanthus amarus and gamophyllous in

Ricinus communis.

Androecium

Stamen one to many, free or united. In Ricinus communis, the stamen is polyadelphous and the filaments are branched. They are fused into

several bundles. Anthers are dithecous. Rudimentary ovary called pistillode is often present in male flowers.

Gynoecium

Ovary superior, tricarpellary and syncarpous. Ovary trilocular with one or two ovules in each locule on axile placentation. Ovary is distinctly three lobed. Styles three, each ending in a bifid stigma.

Fruit

Most commonly schizocarpic capsule or drupe. It is regma in Ricinus communis, dehiscing into three cocci.

Seed

Endospermous.