Family: Apocynaceae (milk weed family) (including Asclepiadaceae)

Family: Apocynaceae (milk weed family) (including Asclepiadaceae)

Systematic position

Diagnostic features

•            Plants with milky sap.

•            Leaves opposite or whorled, exstipulate.

•            Flowers pentamerous.

•            Stamens epipetalous, connate with corona.

•            Fruit a follicle.

•            Stigma is thick and massive often connate to stamen to form Gynostegium

•            Seeds often with coma (hair).

•            Presence of nectariferous disc.

General Characters

Distribution:

This family is represented by 345 genera, 4,675 species. Mostly tropical and subtropical whereas a few species found in temperate region.

Habit: Tree (Alstonia), shrub, (Nerium), herb (Catharanthus), woody twiner (Allamanda, Succulent, Adenium usually twining shrubs with milky sap in laticiferous vessels.

Root: Branched tap root system

Stem: The stems are succulent in some taxa (Stapelia, caralluma), usually erect, branched solid, glabrous, rarely tube like and thick.

Leaves: Simple, undivided, sometimes reduced, exstipulate, opposite decusate (Calotropis) or sometimes alternate (Thevetia) or in whorls of 3 (Nerium), entire, rarely stipulate (Tabernaemontana).

Inflorescence: A Panicle, dichasial cyme,oftenumbelliformin(Asclepiadoids) or raceme, or axillary cluster of two flowers each (Catharanthus).

Flowers: Bracteate, bracteolate, pedicel-late, complete, bisexual, actinomorphic, zy-gomorphic in Ceropegia heterochlamydeous , pentamerous, hypogynous but rarely perigy-nous or epigynous (Plumeria).

Calyx:Sepals5,synsepalous(atleastbasally) sometimes aposepalous (Catharanthus) deeply lobed ; valvate or quincuncial (Thevetia), odd sepal posterior, glandular appendages (Squamellae) present on the adaxial side.

Corolla: Petals 5, sympetalous united into a tube, salver or funnel shaped; twisted or rarely valvate, often hairy within or contain some corona like out growths at the mouth of the corolla tube.

Androecium: Stamens 5 , alternipetalous, often epipetalous, apostemonous to monadelphous, In Asclepiadoids the stamens are connate to the styles to form a gynostegium, pollen grains of each theca of an anther are fused into a waxy mass called pollinium. The right pollinium of each anther attached to the left pollinium of the adjacent anther by a hair like translator, translator arms (retinacula) attached together with the gland like structure called corpusculum. Anthers are dithecous, basifixed, often sagitate, introse; dehisce longitudinally, anthers basally awned; sometimes bear hairy appendages over the lobes (Nerium).

Gynoecium: Bicarpellary, carpels apically united, superior, or rarely half inferior (Plumeria) 1 to 2 locule with 2 to many ovules in each locule on marginal placentation. Style one and simple, stigma is characteristically thickened, massive and bilobed. A nectariferous disc is often present around or at the base of the gynoecium, (Thevetia, Catharanthus, Allamanda and Rauvolfia).

Fruit: The fruit is variable and can be a berry (Landolphia), drupe (Cerbera) follicle (Asclepias), capsule (Allamanda).

Seed: Seeds are endospermous often with crown of hairs.

Botanical description of Catharanthus roseus

Habit: Erect ever blooming ornamental plant with milky latex.

Root: Branched tap root system

Stem: Aerial, erect, cylindrical reddish green, glabrous and branched.

Leaves: Usually simple, opposite decussate, exstipulate, subsessile, or petiolate, elliptic – ovate, entire, mucronate, unicostate reticulate venation.

Inflorescence: cymose, axillary pairs.

Flower: Ebracteate, Ebracteolate, subsessile, complete, bisexual, heterochlamydeous, actinomorphic, hypogynous, pentamerous, rosy purple, white or pink.

Calyx: Sepals 5, slightly synsepalous, green showing valvate aestivation.

Corolla: Petals 5, sympetalous, throat of corolla tube hairy forming a corona, twisted (hypocrateriform).

Androecium: Stamens 5, apostemanous, epipetalous, inserted at the mouth of the corolla tube, filaments short, anthers sagittate, dithecous, dorsifixed, introse.

Gynoecium: Bicarpellary, apocarpous, ovaries superior, unilocular, ovules many, placentation marginal, style simple, stigma hour-glass shaped. Two scaly nectaries are present one on the anterior and another on the posterior side of the ovary.

Fruit: A pair of elongated follicles.

Economic importance of the family Apocynaceae