Systematic Position :
The family includes about 250 genera and 3000 species. The plants are found mostly in tropical and sub tropical areas inhabiting arid soils.
Familiar Plants :
1. Aclepias Curassavica (Silk – Weed).
2. Calotropics gigantean – Tella Jilledu, Sweta archa pushpham
3. C. procera – Rakta Jilledu.
4. Ceropegia bulbosa – Adavipala teega.
5. Cryptostegia grandiflora – Rabbaru teega.
6. Dischidia rafflesiana (Pitcher plant)
7. Gymnema sylvestris – Podapatri
8. Hemidesmus indicus –Sugandhipala, Sarsaparilla.
9. Pergularia daemia – Dushtapu teega.
10. Sarcostemma acidum – Aku jemudu
11. Tylophora indica – Goripala, Mekameyani aku
12. Caralluma edulis.
Habitat and Habit :
Plants are mostly xerophytic parrenial herbs (Aselepias) or shrubs (Calotropis), or woody climbers (Pergularia, Leptadaenia, Cryptolepis etc.) Dischidia is an epiphytic climber. Here one of a pair of leaves is often modified into a pitcher Anatomically the plants resembles with that of Apocyanaceae. The plants possess bicollateral vascular bundles and milky latex.
1. Root : A deep – tap root, rarely adventitious (Dischidia)
2. Stem : Herbaceous or woody, covered in many cases with Wax (calotropis) or with profuse hairs.
3. Leaf : Simple, entire, opposite – decussate, rarely whorled, exstipulated and lamina entire. Pinnate reticulate venation. In Dischidia, leaves are modified into pitchers.
Floral Characters :
1. Inflorescence : Terminal or axillary or sometimes extra axillary (Calotropis), short penduncled. Generally a dichasial cyme, ending in monochasial cymes. This type of inflorescence has been named as Cincinnus (Cryptostegia). Sometimes it is racemose or Umbellate (Asclepias, Calotropis ) cymes. Flowers are solitary as in Stapelia grandiflora.
2. Flower : Pedicellate, bracteates, ebracteolate, actionomorphic, complete, bisexual, hypogynous and pentamerous. (however the carples are only 2)
3. Calyx : Sepals 5, free or basally connate, odd sepal posterior, aestivation imbricate or quicuncial.
4. Corolla : Petals 5, gamopetalous, twisted or valvate aestivation. Corolla tube salver – shaped (Stephonotis), or pitcher like (Ceropegia), or Campanulate (Calotropis), or tubular (Daemia) or funnel – shaped (Crystostegia). The Corolla often posses variously shaped appendages called the corollary corona as its throat. This increases the attraction of the flower. Corona is primarily meant for secreting and strong nectar.
5. Androecium : Stamens are 5 in number, epipetalous and inserted at the base of the corlla tube. In majority of genera, the stamens are monadelphous to form a stamina column or tube surrounding the gynoecium. Staminal corona arises on the outer surface of the stamina column. The anthers are dithecous, introrse, unite with stigmas to form a structure called the gynostegium. The pollen grains are dispersed by insects by a special translator mechanism. Based on the nature of translators, the family is divided into two sub – familes viz. Periplocoideae and Cynanchoideae. In periplocoideae, the translators are spoon shaped (Spathulate ) and the pollen grains are granular in form eg: Cryptostegia. In cynanchoideae, the translator is - shaped and consists of two parts. (i) Corpusculum or gland – like body and (ii) a pair of diverging arms called connectives or retinacula. The pollen grains in each lobe of the anther aggregate to form a mass called pollinium. Eg: Calotropis, Daemia.
6. Gynoecium : Ovary superior, bicarpellary and sub – apocarpous. The carpels are free, have their own ovaries and styles. The two Styles are free at the base, but united at the apex to form a pentangular stigmatic disc. Each carpel has one locule with many ovules on marginal placentation. Ovules are anatropous and bitegmic. The receptive surface is on the edge or underside of the stigmatic head.
7. Fruit : A pair of follicles develop from each flower. The follicles dehisce along the ventral suture to liberate the seeds.
8. Seed : Albuminous and flattened. Usually the seeds have a tuft of hairs arising from the micropylar end (Comose). The coma helps in seed dispersal.
9. Floral Formula :
10. Pollination : Pollination is carried out by bees. Pollination mechanism in this family is unique in many ways, in view of the complicated structure of the flower. The flowers are usually big and brightly coloured. The coronary structures make the flowers more attractive. Nectar is secreted by a disc. The flowers are usually protandrous. In the group Cynanchoideae, the translator has a corpusculum to which pollen masses are attached by elastic threads called retinacula. When the insect moves on the stigmatic head. Accidently its legs slips into the slit between the pollinia. When the insect tries to drag the leg out of the anthers, the translator is dislodged and attaches to the leg. On exposure to air, the pollinia firmly clasp the leg of the insect. When this insect visits another flower for nectar, the pollinial masses are transferred to sticky receptive part of the stigma that is situated underneath. In periplocoideae, the pollen grains are in the form of granular tetrads. The anther lobes of the adjacent anthers shed the pollen into the receptacle of the spoon – shaped translator. The translator has, below the spoon – shaped receptacle, a narrow stalk which bears a sticky disc at the end. The stickly – disc is turned upwards and outwards, so that it can be easily attached to the head of the insect, that is insearch of nectar. When this insect visits another flower, the translator gets deposited on the stigmatic surface thus cacilitating cross pollination.
Economic Importance : Economically, the members of this family have limited importance.
1. Ornamental Plants : A few species like Asclepias curassavica (blood flowers), A. tuberose (butterfly weed), Oxypetalum caeruleum (bule milkweed), Hoya carnosa (Wax plant), Stapelia spp. (Carrion flower) are grown as ornamental plants.
2. Medicine :
(a) The roots of Hemidesmus indicus yield ‘Sugandipalu’ which is extensively used in preparation of medicines.
(b) Roots of Oxystelma are used for treatment of jaundice.
(c) The roots and leaves of Tylophora indica are used medicinally against asthma
(d) The dried stem of sarcostemma acidum is emetic and emetic and an infusion of the roots is used as antidote for sanke bite.
(e) The plant Cynanchum arnottianum is used as an insecticide.
(f) The leaves of Gymmema sylvestre are used to treat diabetes.
3.Rubber :The latex of Cryptostegia grandiflora is a source of cheap quality rubber.
4. Others :
(a) The blast fibre obtained from the stems of Asclepias, Tylophora, Leptadenia, Calotropis is used for cordage, fishing nets and twines.
(b) The seed hairs of Asclepias are used as substitute for ‘kapok’. The hair are fine, silky and light.
(c) Latex of Matalea, is used as an arrow poison.
Distinguishing Features :
1. Perennial erect herbs or shrubs with milky latex.
2. Leaves with opposite – decussate phyllotaxy.
3. Presence of bicollateral vascular bundles.
4. Exstipulate leaves.
5. Axillary or terminal cymose umbels.
6. Flowers regular, bisexual and hypogynous.
7. Presence of gynostegium, translators.
8. Bicarpellary, sub – apocarpous ovary
9. Ovary unilocular, placentation marginal.
10. Fruit a pair of follicles, seeds with comose hairs
The family includes two sub – families :
1. Periplocoideae: Pollen in tetrads, translator spoon shaped. Eg: Cryptostegia.
2. Cynanchoideae : Pollen united into pollinia, translator -shaped Eg: Calotropis.
Taxonomic Affinities :
The family is closely related to Apocyanaceae. So Bentham and Hooker placed the family along with Apocynaceae in the order Gentianales. Engler and Prantl included it in the order Contortae of Sympetalae.
1. Presence of latex.
2. Exstipulate leaves, opposite phyllotaxy.
3. Regular flowers, hypogynous.
4. Presence of corollary corona.
5. Epipetalous stamens.
6. Carpels 2,marginal placentation
7. Nuclear type of endosperm
8. Winged or hairy seeds.