In this article we will discuss about:- 1. Characters of Asclepiadaceae 2. Distribution of Asclepiadaceae 3. Economic Importance 4. Affinities 5. Important Types.
Characters of Asclepiadaceae:
Plants herbs, shrubs, mostly twiners and rarely trees; leaves opposite, simple, entire margin rarely alternate; inflorescence cymose or racemose; flowers hermaphrodite, pentamerous; calyx of 5 sepals, imbricate; petals 5, gamopetalous, corona arising as outgrowth of petals or stamens; stamens 5, fused with stigmatic disc forming gynostegium; pollens forming pollinia; carpels bicarpellary, syncarpous, ovaries and style free, only stigma fused to form disc, marginal placentation, fruit follicles.
A. Vegetative characters:
Habit:
Perennial herbs (Asclepias) or shrubs (Calotropis, Leptadenia), climbers (Cryptostegia, Daemia), succulent (Stapelia) with latex.
Root:
A deep branched tap root.
Stem:
Herbaceous, week and climbing or succulent, woody below (Calotropis), erect, twiner or climbers (Cryptostegia) cylindrical, rarely hairy and solid, latex present.
Leaves:
Simple, petiolate, exstipulate, entire, opposite rarely whorled, waxy; in Dischidia rafflesiana leaves are modified into pitchers, reduced or absent (Periploca), succulent in Hoya.
B. Floral characters:
Inflorescence:
Mostly umbellate cymes (Calotropis) or dichasial cyme ending in monochasial cyme.
Flower:
Bracteate or ebracteate, pedicellate, complete, hermaphrodite, actinomorphic, rarely zygomorphic (Ceropegia), pentamerous, hypogynous.
Calyx:
Sepals 5, polysepalous or gamosepalous-fused near the base, quincuncial aestivation, sometimes valvate.
Corolla:
Petals 5, gamopetalous, 5 lobed, twisted aestivation or valvate, corona may be scaly or hairy out growth from petals – corolline corona in Cryptostegia, Cryptolepis or form staminal tube i.e. staminal corona in Calotropis and Asciepias.
Androecium:
Stamens 5, synandrous, gynostegium (stamens fused with stigmatic disc to form gynostegium), anthers dithecous, epipetalous, coherent; the pollen grains of each half anther usually agglutinated into granular mass of tetrads or waxy pollen called pollinium (Asclepias, Calotropis). Thus each stamen has two pollinia.
The pollinia of two adjacent anther halves are connected together at the black, dot-like gland called corpusculum by appendages called – retinacula. The two pollinia (of adjacent anther halves), two retinacula and a corpusculum together form a single translator. So in all there are 5 translators.
Gynoecium:
Bicarpellary, syncarpous, ovaries free, superior, enclosed in staminal tube, ovules many on marginal placentation, each carpel is unilocular; style 2, free, distinct; stigmas united to form a pentangular disc with which anthers are fused to form gynostegium.
Fruit:
An etaerio of two, often widely divergent follicles; in some one follicle is abortive.
Seed:
Many small, compressed with long silky hairs.
Pollination:
Entomophilous, translator mechanism.
Floral formula:
Distribution of Asclepiadaceae:
The family Asclepiadaceae is commonly known as ‘Milk weed family’. In includes 320 genera and 2,000 species of world wide distribution, but mostly confined to tropics and sub-tropics. In India 332 species belonging to 35 genera are found.
Economic Importance of Asclepiadaceae:
1. Food:
Gymnema lactiferum yields latex which is used as food in Ceylon.
2. Fibres:
Some plants like Daemia extensa, Calotropis procera, C. gigantea, Marsdenia and Leptadenia etc. yield silky fibres which axe used for making ropes, mat, stuffing pillows etc.
3. Medicinal:
The source of medicine in the family is latex from which alkaloids are extracted. The roots of Oxystelma esculentum are specific for jaundice. This roots of Pentatropis are used in gonorrhoea. Hemidesmus indicus is used in leucorrhoea, rheumatism and in snake bites. Daemia extensa is used in cough; asthma and diarrhoea.
4. Rubber:
Cryptostegia grandiflora is a natural source of rubber in India.
5. Poison:
Some species of Asclepias are important as live-stock poison. The sap of Matelea has been used as an arrow poison.
6. Ornamental:
Asclepias, Cryptostegia, Hoya, Huernia, Ceropegia, Periploca etc. are cultivated for ornamental purposes.
Primitive characters:
1. Plants mostly shrubs rarely herbs.
2. Leaves simple.
3. Flowers hermaphrodite, hypogynous, actinomorphic.
4. Calyx polysepalous in some species.
5. Gynoecium partly apocarpous.
6. Marginal placentation.
7. Fruits usually etaerio of follicles.
8. Seeds endospermic.
Advanced characters:
1. Leaves exstipulate and usually opposite.
2. Corolla gamopetalous.
3. Corona present.
4. Stamens epipetalous and filaments fused to form a tube around the gynoecium.
5. Anthers coherent with stigmatic disc to form gynostegium.
6. Pollen grains are grouped to form pollinia.
7. Carpels two.
8. Seeds covered with hygroscopic hairs.
Affinities of Asclepiadaceae:
The family Asclepiadaceae is closely allied to the family Apocynaceae, from which it differs in following respects:
1. Absence of pollinia in the Apocynaceae.
2. No translator mechanism in the Apocynaceae.
3. In Apocynaceae stamens are not fused with stigma to form gynostegium. Rest of the phylogeny has been discussed under Apocynaceae.
Common plants of the family:
1. Asclepias (Milk weed) – A red flowered plant.
2. Calotropis procera (H. Aak) – A xerophytic wild shrub.
3. Cryptostegia grandiflora – A large, stout climber.
4. Periploca calophylla – Shrub with coriaceous lanceolate leaves.
5. Gymnema tingens – Twining herb.
6. Marsdenia tenacissima (Rajmahal hemp) – A climbing shrub with very short stem.
7. Hoya longifolia (Wax plant) – A twining epiphyte with waxy leaves and flower.
8. Sarcostemma brevistigma – A wild plant.
9. Sarcolobus globosus – A climber which occurs in Sunderbans.
Division of the family and chief genera:
The Asclepiadaceae is divided on the basis of pollen characters into 2 sub-families and four tribes:
Sub-family I. Cynanchoideae:
Pollen aggregated into 2-4 waxy bodies called pollinia.
Tribe 1. Asclepiadeae:
Pollinia 2 in each anther, e.g. Asclepias, Calotropis.
Tribe 2. Gonolobeae:
Pollinia in pairs in each anther, but transverse; e.g. Gonolobus.
Tribe 3. Secamoneae:
Pollinia 4 in each anher, i.e. 20 in all; e.g. Secamone.
Tribe 4. Tyiophoreae:
Pollinia in pairs in each anther but erect; e.g. Marsdenia.
Sub-family II. Periplocoideae:
Pollen granular and in tetrads; translators, spoon-shaped and provided with adhesive disc; e.g. Cryptolepis, Hemidesmus.
Important Types of Asclepiadaceae:
1. Calotropis procera (H. Aak) (Fig. 73.2):
Habit:
A perennial wild, xerophytic shrub of fallow land and waste places.
Root:
Tap, branched, perennial and very deep.
Stem:
Erect, woody below and herbaceous above, cylindrical, solid, branched, hairy, rough, latex present.
Leaves:
Opposite decussate, simple, sessile, exstipulate, semiamplexicaul, ovate-elliptical, entire, thick, leathery, covered with hair and wax, unicostate reticulate venation.
Inflorescence:
Axillary umbellate cymes.
Flower:
Bracteate, pedicellate, complete, hermaphrodie, actinomorphic, pentamerous, hypogynous.
Calyx:
Sepals 5, polysepalous, greenish, quincuncial.
Corolla:
Petals 5, gamopetalous, campanulate, inner side purple twisted.
Androecium:
Stamens 5, epipetalous, filament connate forming a staminal tube around ovary; anthers fused to the margins of pentangular stigmatic disc forming gynostegium; pollen grains aggregated into small ovoid vescicles – the pollinia; each anther possessing 2 pollinia.
Pollinia of adjacent anthers are united by means of 2 retinacula arising from a brownish-black dot-like the corpusculum (Fig. 73.2). From the back of the staminal column five, fleshy, laterally compressed coloured coronary outgrowths radiate out. These are known as cuculi.
Gynoecium:
Bicarpellary, syncarpous, superior, ovaries free below and united in stylar region and finally terminates in a pentangular stigmatic head which is confluent with pollinia forming gynostegium. Each ovary unilocular, marginal placentation.
Floral formula:
2. Asclepias curassavica (Fig. 73.3):
Habit:
A perennial herb.
Root:
Tap, branched and perennial.
Stem:
Erect, herbaceous, cylindrical, solid, branched, green, hairy with latex.
Leaves:
Opposite decussate, simple, petiolate, exstipulate, lanceolate, entire, acuminate unicostate reticulate venation.
Inflorescence:
Axillary umbellate cyme.
Flower:
Ebracteate, pedicellate, complete, hermaphrodite, actinomorphic, pentamerous, hypogynous, purple yellow.
Calyx:
Sepals 5, polysepalous green, quincuncial.
Corolla:
Petals 5, gamopetalous, petals reflexed, twisted.
Corona:
Five, fleshy, laterally compressed coloured coronary outgrowths radiating from staminal column.
Androecium:
Stamens 5, filaments connate forming a staminal tube around the ovary, anthers fused to be margins of the pentangular stigmatic disc forming gynostegium; pollen grains aggregated into 10 small vescicle like pollinia; each anthers possessing 2 pollinia; pollinia of adjacent anthers joined to a corpusculum by retinacula (or caudicles).
Gynoecium:
Bicarpellary, syncarpous, superior, unilocular, marginal placentation with many ovules, stigma 5-angled, enlarged, stigmatic head prominent and pentangular.
Floral formula:
