In this article we will discuss about:- 1. General Features of the Asclepiadaceae 2. Floral Range in the Asclepiadaceae 3. Divisions 4. Number and Distribution 5. Commonly Occurring Plants 6. Economic Aspects.
General Features of the Asclepiadaceae:
Habit – Herbs or shrubs, with latex.
Leaves – Opposite, simple, entire, exstipulate.
Flowers – Bisexual, regular, hypogynous.
Calyx – Sepals 5, united, quincuncial.
Corolla – Petals 5, united, valvate, provided with horn-like appendages (corona).
Androecium – Stamens 5, epipetalous; anthers adnate to stigma; pollen grains cohere to form pollinia and attached to a black horny structure called translator or caudicle; pollinia united in pairs or tetrads to a gland (retinaculum) on stigma.
Gynoecium – Carpels 2, free below; ovules many on marginal placentae; stigma five-angled to which anthers adhere (gynostegium), each angle of stigma being accompanied by a sticky disc (corpusculum) on groove.
Fruit – Pair of follicles.
Seeds – Comose; embryo large, straight; endosperm scanty, cartilaginous.
Floral Range in the Asclepiadaceae:
In general, the flowers are small. But large flowers are found in Ceropegia, Stapelia and Stephanotis.
The flowers are usually regular, but irregular flowers are sometimes met with. The corolla is divided and forms a rotate structure, but the tube may be longer and constitute a pitcher-like corolla (Ceropegia) or salver form corolla (Stephanotis). One can find the occurrence of corona-like appendages which spring from the corolla itself or from the back of the stamens.
The ovary is usually apocarpous, but the styles are united to form a swollen head or may become beaked or somewhat conical or flattened.
Divisions of the Asclepiadaceae:
Based on pollen grain characters, the Asclepiadaceae is divided into two subfamilies with four tribes in one subfamily and none in the other subfamily:
Subfamily I. Cynanchoideae:
Pollen aggregated into two to four waxy bodies called pollinia.
Tribe (i) Asclepiadeae:
Pollinia 2 in each anthers, i.e., 10 in all. Examples- Asclepias, Calotropis, etc.
Tribe (ii) Gonolobeae:
Pollinia in pairs in each anther but transverse. Example- Gonolobus.
Tribe (iii) Secamoneae:
Pollinia 4 in each anther, i.e., 20 in all. Examples: Genianthus, Secamone, etc.
Tribe (iv) Tylophoreae:
Pollinia in pairs in each anther, but erect. Examples- Marsdenia, Tylophora, etc.
Subfamily II. Periplocoideae:
Pollen granular and in tetrads; translators spoon-shaped and provided with an adhesive disc. Examples- Cryptolepis, Hemidesmus, etc.
Number and Distribution of the Asclepiadaceae:
There are about 250 genera and 1,800-2,000 species in the Asclepiadaceae. The members of the family are mainly distributed in the tropics of the Old World, although some are found in tropical America.
Commonly Occurring Plants of the Asclepiadaceae:
Asclepias curassavicci L. is an erect perennial herb which occurs in waste places.
Giant Milkweed or Madar [Calotropis gigantea (L.) R. Br. ex Ait.] is a large shrub covered with a woolly tomentum.
Swallow-wart [Calotropis procera (Willd.) Dryand ex. Ait.] is an erect white downy shrub.
Caralluma fimbriata Wall, is a succulent herb.
Cryptolepis buchanani Roem. & Schult. is found in hedges.
Cryptostegia grandiflora (Roxb.) R. Br. is a large stout garden climber.
Cynanchum callialata Ham. is a twining shrub.
Decalepis hamiltonii Wt. & Arn. is a climbing shrub with jointed stems.
Dischidia rafflesiana Wall, is a stout twiner with pitchers whose cavity is filled with rain water and adventitious roots.
Dregea volubilis (L. f.) Benth. ex Hook. f. is a tall stout climber.
Finlaysonia maritima (Bl.) Backer ex K. Heyne is a large climber of the Sunderbans.
Indian Sarsaparilla [Hemidesmus indicus (L.) Schult.] is a thin twining shrub.
Wax plant (Hoya parasitica Wall.) is a twining epiphyte with waxy leaves and flowers.
Rajmahal Hemp [Marsdenia tenacissima (Roxb.) Moon] is a climbing shrub with a very short stem.
Oxystelma secamone (L.) Karst. is a perennial climbing herb.
Pentatropis capensis (L.f.) Bullock is a twining slender herb of the Sunderbans.
Pergularia daemia (Forsk.) Chiov. is a climbing undershrub, bearing spinous follicles.
Sarcolobus carinatus Wall, is a climber which occurs in the Sunderbans.
Sarcostemma acidum (Roxb.) Voigt commonly occurs in dry areas of Peninsular India.
Telosma minor (Andr.) Craib is a twining glabrous undershrub.
Tylophora indica (Burm. f.) Merr. is a twining slender herb.
Economic Aspects of the Asclepiadaceae:
Economically, the members of the Asclepiadaceae are of some importance. Some species of Asclepias act as livestock poisons. The seed hairs of A.curassavica, A. incarnata and A.syriaca are used as a substitute for ‘kapok’. The fleshy stems of Caralluma fimbriata and tubers of Ceropegia pusilla are edible. A few plants are used medicinally, e.g. Calotropis, Caralluma and Hemidesmus indicus.
From the bark of Calotropis gigantea, C. procera, Leptadenia pyrotechnica and Marsdenia tenacissima fibres are extracted. Ceropegia, Hoya, Oxypetalum, Periploca, Stapelia, etc. are planted for ornament. Cryptostegia grandiflora and C. madagascariensis form good sources of rubber.
The latex of Gymnema lactiferum (Sri Lanka) is used as a substitute for milk. Marsdenia cundurango supplies ‘cundurango bark’. M. tinctoria yields an indigo-like dye. The latex of Matelea is utilised as an arrow poison. Oxystelma secamone has drinkable milk.
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