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ASCLEPIADACEAE.pdf

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ANAKHA JACOB

About 250 genera and 2000 species distributed mainly in tropical and subtropical regions and a few also in temperate regions. Erect or twining perennial herbs (Asclepias), shrubs (Calotropis procera), vines (Leptadenia), or rarely small trees (Calotropis gigantea). Cryptostegia grandiflora is a stout climbing shrub. Leaves, usually simple, opposite decussate. Rarely alternate/ whorled. Inflorescence, mostly dichasial or polychasial cyme.Flower, Bracteate, often bracteolate, complete; actinomorphic, rarely zygomorphic (Ceropegia), hermaphrodite, pentamerous (except the gynoecium), hypogynous, cyclic. Perianth biseriate. A nectariferous corona, consisting of 5 hoods may be present. Depending upon the condition of androecium, two subfamilies are recognised. Gynoecium: Bicarpellary, the carpels are free below but united by their apices into the single 5-lobed stigma; ovary superior. Fruit: A follicetum of 2 follicles (commonly 1 abort). Based on pollen characters, Asclepiadaceae is divided into two subfamilies, viz. (i) Periplocoideae (pollen grains in tetrads; filaments free), and (ii) Cynanchoideae (pollen grains united in pollinia; filaments united in a tube). Asclepiadaceae is most closely allied to Apocynaceae, and in majority of the systems of classification both these families are placed side by side. However, the characters such as presence of translators and presence of gynostegium are absent in Apocynaceae

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ASCLEPIADACEAE (Milkweed family) Habitat & Distribution • About 250 genera and 2000 species distributed mainly in tropical and subtropical regions and a few also in temperate regions. • Mostly mesophytes. Some are xerophytic (Caralluma, Stapelia). • Dischidia species are epiphytic. Habit • Erect or twining perennial herbs (Asclepias), shrubs (Calotropis procera), vines (Leptadenia), or rarely small trees (Calotropis gigantea). Cryptostegia grandiflora is a stout climbing shrub. • Some herbs perennate by means of a fascicle of thick fleshy roots (Ceropegia). • Usually with milky sap. • Epiphytic species like Dischidia possess adventitious roots which help in climbing. Some leaves form pitchers in which organic debris and water get collected and adventitious roots produced into them absorb the nutrients. • Rootstock fleshy, tuberous, woody, or sometimes absent. • Xerophytes like Caralluma, Stapelia show thick succulent or cactus-like stems and leaves reduced to scales or spines. • Leaves • Usually simple, opposite decussate. Rarely alternate/ whorled. • Leaves caducous or vestigial in some xerophytes. • Stipules usually absent or if present, minute. • Margins generally entire. • Often have a waxy coating. Inflorescence • Mostly dichasial or polychasial cyme. Racemose or umbellate (Stapelia) are seen rarely. • Extra-axillary, short or long peduncled umbellate cymes, fundamentally dichasial but ending in monochasial cymes. Class: Dicotyledons Subclass: Gamopetalae Series: Bicarpellatae Order: Gentianales
Flower • Bracteate, often bracteolate, complete; actinomorphic, rarely zygomorphic (Ceropegia); hermaphrodite, pentamerous (except the gynoecium), hypogynous, cyclic. • Perianth biseriate. Calyx: 5 free or basally connate sepals forming a short tube; valvate, imbricate, or quincuncial. Corolla: • 5 petals, gamopetalous; mostly contorted, rarely imbricate or valvate. • Corolla tube often short and with lobes; corolla tube is zygomorphic in Ceropegia, funnel form in Cryptostegia and campanulate in Gymnema. • Often the corolla tube is with a corona, made up of a ring of scales, hairs or processes. • Corolla lobes often terminated by a morphologically highly variable faucal annulus. Androecium: 5 stamens, arising from the base of the corolla and alternating with its lobes. Rarely distinct and usually adnate or adherent to the gynoecium to produce gynostegium (comparable to the column in Orchidaceae). The fleshy dorsal processes of stamens from the staminal corona. A nectariferous corona, consisting of 5 hoods may be present. These hoods are sometimes mistaken for petals. A beak or hood may be associated with each hood of a corona. Anthers are usually 2-celled and biloculate (4-celled in Secamone). Each cell produces a pollinial mass which is waxy. In some glandular pollen grains are united into tetrads. Depending upon the condition of androecium, two subfamilies are recognised: Cynanchoideae Periplocoideae 230 genera with complex mechanism. 48 genera with simple mechanism Pollen grains at maturity agglutinated within each anther sac into a sac-shaped pollinium, the pollinia united in pairs, each pollinium bearing a translator arm and the translator Pollen is granular, but the grains united in tetrads with each of the 5 translator arms concavely spoon- or cornucopia-shaped and ending below in an adhesive disc, the pollen
arms of each pair themselves joined by a roughly sagittate body called the gland (corpusculum). tetrads at maturity falling into the spoon or horn. Gynoecium: • Bicarpellary, the carpels are free below but united by their apices into the single 5-lobed stigma; ovary superior. • Ovary of each carpel is unilocular; numerous anatropous and pendulous ovules imbricated in several series on a ventral and parietal placenta in each locule, marginal placentation. • Styles 2 • Stigma 1 and 5-lobed, much enlarged (discoid/conical/beaked) is nonreceptive except for the 5 longitudinal strips of glandular stigmatic surface on the thickened edge or the lower side exposed between the contiguous anthers. Fruit • A follicetum of 2 follicles (commonly 1 abort). • Seeds (with few exceptions) with a tufted micropylar coma of long silky hairs, the embryo large, endosperm thin and small. Pollination Cyanchoideae: Each stamen forms two pollinial masses from its anther. A pollinial mass is formed when all the pollen grains of an anther lobe are agglutinised. A translator is formed between two anthers. The translator is spoon-shaped, and they are 5 in number. A translator consists of corpusculum attached to the margin of stigmatic head and two diverging hard arms called connectives or retinacula which are joined to two waxy pollinial masses of contiguous anthers. The insect which visits a flower of this type for nectar gets its legs entangled in the slit or small space between the anthers. So, while pulling out its legs free from the slits, it pulls out the whole translator. Due to hygroscopic action of retinacula, the pollinial masses come together and firmly clasp around the legs so that they are not lost during the flight of the insect. In its visit to another flower, it deposits the pollinial masses on the receptive surface of the stigma. The translator mechanism helps in removing the pollen by the insect during pollination.
Periplocoideae: The stamens have filaments and the granular pollen is united into tetrads. The five translators between the anthers are spoon-like with a sticky disc at the base. The pollen from the two halves of the adjacent stamens is poured into these structures. At the time of pollination, the sticky basal disc turns outwards and gets adhered to the insect. The insect will carry the spoon-like translator with its pollen and during its visit to another flower, deposits it on the receptive undersurface of the stigmatic head. Economic Importance Ornamentals Hoya, Caralluma, Asclepias, Oxypetalum, huernia, Stapelia Fibre used for cordage, twines, fishing nets etc. From Asclepias curassavica (blood flower), Calotropis gigantea, Cosmstigma racemose, Leptadenia pyrotechnica, Marsdenia roylei, M. tinctorial, Tylophora tenuis. Indigo-like dye Marsdenia tinctoria Rubber Cryptostegia grandiflora Arrow poison Latex from Matelea. Medicinal Calotropis procera: roots against cough. Gymnema sylvestre: laxative and diuretic. Hemidesmus indicus: roots in urinary and skin diseases. Holostemma rheedianum: roots used in cough and cold. Pergularia daemia: used as an emetic and expectorant Sarcostemma acidum: infusion of roots is used as an antidote for snakebite Tylophora indica: roots used in curing bronchitis, whooping cough and asthma. Edible Ceropegia hirsuta: roots are edible C. oculate & C.lawii: tubers edible. Stuffing material Floss from seeds used as stuffing material Gunpowder charcoal From the wood of Calotropis gigantea. Systematics and Phylogeny (Affinities)
Based on pollen characters, Asclepiadaceae is divided into two subfamilies, viz. (i) Periplocoideae (pollen grains in tetrads; filaments free), and (ii) Cynanchoideae (pollen grains united in pollinia; filaments united in a tube). Asclepiadaceae is most closely allied to Apocynaceae, and in majority of the systems of classification both these families are placed side by side. However, the characters such as presence of translators and presence of gynostegium are absent in Apocynaceae.

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ASCLEPIADACEAE.pdf

  • 1. ASCLEPIADACEAE (Milkweed family) Habitat & Distribution • About 250 genera and 2000 species distributed mainly in tropical and subtropical regions and a few also in temperate regions. • Mostly mesophytes. Some are xerophytic (Caralluma, Stapelia). • Dischidia species are epiphytic. Habit • Erect or twining perennial herbs (Asclepias), shrubs (Calotropis procera), vines (Leptadenia), or rarely small trees (Calotropis gigantea). Cryptostegia grandiflora is a stout climbing shrub. • Some herbs perennate by means of a fascicle of thick fleshy roots (Ceropegia). • Usually with milky sap. • Epiphytic species like Dischidia possess adventitious roots which help in climbing. Some leaves form pitchers in which organic debris and water get collected and adventitious roots produced into them absorb the nutrients. • Rootstock fleshy, tuberous, woody, or sometimes absent. • Xerophytes like Caralluma, Stapelia show thick succulent or cactus-like stems and leaves reduced to scales or spines. • Leaves • Usually simple, opposite decussate. Rarely alternate/ whorled. • Leaves caducous or vestigial in some xerophytes. • Stipules usually absent or if present, minute. • Margins generally entire. • Often have a waxy coating. Inflorescence • Mostly dichasial or polychasial cyme. Racemose or umbellate (Stapelia) are seen rarely. • Extra-axillary, short or long peduncled umbellate cymes, fundamentally dichasial but ending in monochasial cymes. Class: Dicotyledons Subclass: Gamopetalae Series: Bicarpellatae Order: Gentianales
  • 2. Flower • Bracteate, often bracteolate, complete; actinomorphic, rarely zygomorphic (Ceropegia); hermaphrodite, pentamerous (except the gynoecium), hypogynous, cyclic. • Perianth biseriate. Calyx: 5 free or basally connate sepals forming a short tube; valvate, imbricate, or quincuncial. Corolla: • 5 petals, gamopetalous; mostly contorted, rarely imbricate or valvate. • Corolla tube often short and with lobes; corolla tube is zygomorphic in Ceropegia, funnel form in Cryptostegia and campanulate in Gymnema. • Often the corolla tube is with a corona, made up of a ring of scales, hairs or processes. • Corolla lobes often terminated by a morphologically highly variable faucal annulus. Androecium: 5 stamens, arising from the base of the corolla and alternating with its lobes. Rarely distinct and usually adnate or adherent to the gynoecium to produce gynostegium (comparable to the column in Orchidaceae). The fleshy dorsal processes of stamens from the staminal corona. A nectariferous corona, consisting of 5 hoods may be present. These hoods are sometimes mistaken for petals. A beak or hood may be associated with each hood of a corona. Anthers are usually 2-celled and biloculate (4-celled in Secamone). Each cell produces a pollinial mass which is waxy. In some glandular pollen grains are united into tetrads. Depending upon the condition of androecium, two subfamilies are recognised: Cynanchoideae Periplocoideae 230 genera with complex mechanism. 48 genera with simple mechanism Pollen grains at maturity agglutinated within each anther sac into a sac-shaped pollinium, the pollinia united in pairs, each pollinium bearing a translator arm and the translator Pollen is granular, but the grains united in tetrads with each of the 5 translator arms concavely spoon- or cornucopia-shaped and ending below in an adhesive disc, the pollen
  • 3. arms of each pair themselves joined by a roughly sagittate body called the gland (corpusculum). tetrads at maturity falling into the spoon or horn. Gynoecium: • Bicarpellary, the carpels are free below but united by their apices into the single 5-lobed stigma; ovary superior. • Ovary of each carpel is unilocular; numerous anatropous and pendulous ovules imbricated in several series on a ventral and parietal placenta in each locule, marginal placentation. • Styles 2 • Stigma 1 and 5-lobed, much enlarged (discoid/conical/beaked) is nonreceptive except for the 5 longitudinal strips of glandular stigmatic surface on the thickened edge or the lower side exposed between the contiguous anthers. Fruit • A follicetum of 2 follicles (commonly 1 abort). • Seeds (with few exceptions) with a tufted micropylar coma of long silky hairs, the embryo large, endosperm thin and small. Pollination Cyanchoideae: Each stamen forms two pollinial masses from its anther. A pollinial mass is formed when all the pollen grains of an anther lobe are agglutinised. A translator is formed between two anthers. The translator is spoon-shaped, and they are 5 in number. A translator consists of corpusculum attached to the margin of stigmatic head and two diverging hard arms called connectives or retinacula which are joined to two waxy pollinial masses of contiguous anthers. The insect which visits a flower of this type for nectar gets its legs entangled in the slit or small space between the anthers. So, while pulling out its legs free from the slits, it pulls out the whole translator. Due to hygroscopic action of retinacula, the pollinial masses come together and firmly clasp around the legs so that they are not lost during the flight of the insect. In its visit to another flower, it deposits the pollinial masses on the receptive surface of the stigma. The translator mechanism helps in removing the pollen by the insect during pollination.
  • 4. Periplocoideae: The stamens have filaments and the granular pollen is united into tetrads. The five translators between the anthers are spoon-like with a sticky disc at the base. The pollen from the two halves of the adjacent stamens is poured into these structures. At the time of pollination, the sticky basal disc turns outwards and gets adhered to the insect. The insect will carry the spoon-like translator with its pollen and during its visit to another flower, deposits it on the receptive undersurface of the stigmatic head. Economic Importance Ornamentals Hoya, Caralluma, Asclepias, Oxypetalum, huernia, Stapelia Fibre used for cordage, twines, fishing nets etc. From Asclepias curassavica (blood flower), Calotropis gigantea, Cosmstigma racemose, Leptadenia pyrotechnica, Marsdenia roylei, M. tinctorial, Tylophora tenuis. Indigo-like dye Marsdenia tinctoria Rubber Cryptostegia grandiflora Arrow poison Latex from Matelea. Medicinal Calotropis procera: roots against cough. Gymnema sylvestre: laxative and diuretic. Hemidesmus indicus: roots in urinary and skin diseases. Holostemma rheedianum: roots used in cough and cold. Pergularia daemia: used as an emetic and expectorant Sarcostemma acidum: infusion of roots is used as an antidote for snakebite Tylophora indica: roots used in curing bronchitis, whooping cough and asthma. Edible Ceropegia hirsuta: roots are edible C. oculate & C.lawii: tubers edible. Stuffing material Floss from seeds used as stuffing material Gunpowder charcoal From the wood of Calotropis gigantea. Systematics and Phylogeny (Affinities)
  • 5. Based on pollen characters, Asclepiadaceae is divided into two subfamilies, viz. (i) Periplocoideae (pollen grains in tetrads; filaments free), and (ii) Cynanchoideae (pollen grains united in pollinia; filaments united in a tube). Asclepiadaceae is most closely allied to Apocynaceae, and in majority of the systems of classification both these families are placed side by side. However, the characters such as presence of translators and presence of gynostegium are absent in Apocynaceae.