Botanical origin : Calotropis procera Family : Asclepiadaceae Arka, an important drug of Ayurveda is known in this country from the earliest time. It is mentioned by the earliest Hindu writers and the ancient name of the plant which occurs in the vedic literature was Arka alluding to the form of leaves, which was used in the sacrifical rites. There are two common species of Calotropis, viz. C. gigantea (Linn.) R.Br. and C. procera (Ait.) R.Br. described by the Sanskrit writers. Both the species are used as substitutes for one another and are said to have similar effects. One species is more commonly used in some parts of the country, while the other parts use the other species depending on the availability of their distribution. Although C. gigantea is said to be distributed throughout India ascending to 100 m Himalayas, it has been observed that it is not easily available in certain localities, even in plains, where C. procera is more widely distributed and hence being commonly used and known as Arka or Madar. C. procera is almost exclusively North Indian source C. procera is slightly smaller than C. gigantea and has a more compact habit. In Dhanvantari Nigantu three varieties of Arka are mentioned viz. Rajarkah, Suklarkah and Sveta mandarah (Aiyer and Kolammal, 1963) Sanskrit Synonyms Arka, Alaka, Ravi, Shvetamandara, Haridashwa, Pushpaka, Vasuka, Bhanu, Ushmarashmi, Kheere, Mandara, etc. Regional names Bengali : Swetakonda,Aankada etc. Behari : Moortakanda. Dravid : Yorikke Gujarati : Aakado,Akro,Nihanoakdo etc. Hindi : Aaka, Aanka, Ak, Ark, Arka, Aka, Madara etc. Kashmir : Aka Urdu : Ak Marathi : Ruee,Lal madar,Mudi etc. Tamil : Arukkan,Erukama etc. Telugu : Jilledachetta,Mandaram etc. English : Mudar,Madar,Giant milk weed,Muda-yercum etc. Parts used : Root, Leaf, Flowers and Latex. Properties and uses : All the parts, viz, root, stem, leaf and flowers of Calotropis are in common use in indigenous system of medicine. The drug is hot, bitter, pungent and laxative and is beneficial in skin diseases, ulcers, enlargement of the spleen, abdominal glands, liver diseases, promotes digestive power and also useful in colics. The milky exudate is bitter, hot, demulcent and is useful in skin diseases, tumour and ascitis. It is a very good purgative. The root bark is considered as a valuable remedy in skin diseases, enlargement of abdominal viscera, intestinal worms, cough, ascites etc. The milky juice is regarded as a drastic purgative and is used in combination with the juice of the Euphorbia nerifolia. The root bark in the form of paste with rice vinegar is applied to elephantiasis of the legs and scrotum. It also acts as a emetic in doses of 30 to 60 g and has been used as a substitute for ipecacuanha (Chopra et al., 1958). The flowers are considered to be sweet, bitter, digestive, stomachic, tonic and useful in cough, asthma and catarrh. Flowers are also employed in skin diseases, worms, mucus, haemorrhage caused by the mutual and simultaneous vitiation of rakta and pitta (Aiyer and Kolammal 1963, Nadkarni, 1954, Sharma, 1969). Botanical Description: Calotropis procera is an erect, perennial shrub luxuriantly thriving in wastelands. It is a hardy branched, large sized erect, profusely milky shrub, 9-24 high, usually with only a very short thick stumpy stem. Leaves: Leaves are opposite, sub sessile, oblong, acute. Umbels: Cottony, old glabrous, long peduncled. Corolla: Lobes erect, coronal scale acute, glabrous or pubescent. Stamens: 5, adhering around the staminal axis, anther cells with a solitary pollen mass in each, pendulous flattened tips of the anthers, membraneous, inflexed. Follicles: 8.5-10.5 cm, recurved. Seeds : Ovoid. Distribution : Common in Western and Central India from Punjab to Bihar and Bombay. Also distributed in Persia, Tropical Africa (Hooker,1885). Often found as a weed in agricultural lands. Macroscopical Characters : ROOt The root occurs in the entire condition. The bark is separated from the wood 0.5-2.0 cm. in diameter bearing rootlets with diameter varying from 0.2 to 0.5 cm. Externally whitish grey in colour, wrinkled in the fresh condition, plenty of whitish latex exudes from cuts or wounds in the bark. Leaf Simple, opposite, sub-sessile, slightly thick, fleshy, coriacious, 10-15 cm. long and 4.5 to 6.5 cm. broad, broadly cuneate, obovate or obovate oblong, slightly cordate and auricled at base with tuff of short simple hairs on the upper side near place of the attachment to the petiole. The tender leaves are covered with ashy gray pubescence. Mature leaves are nearly smooth or even glabrous and pale green (Aiyer and Kolammal, 1963, Chaudhury,1961). Flowers Regular,bisexual, liliac or pale rose, purple or light greenish yellow and have a faint odour. They are arranged in simple or rarely compound cymose corymbs at the ends of laterally placed or interpetiolar peduncles arising from alternate sides of the nodes. Each cluster is surrounded by an involucre of several small oblong pointed scaly caducous bracts. Flower buds ovoid (Plate 7A). Calyx : Five lobes broadly ovate with small fleshy teeth like glands within the base. Corolla : Regular, gamopetalous, pale rose purple or liliac, subcordate to broadly sub- campanulate with a short tube and five broad ovate, lanceolate, valvate, spreading lobes. Stamens : Five, inserted at the base of the corolla. Filaments united to form a large staminal column provided with five conspicuous radiating coronal appendages that are completely adnate to, but slightly shorter than the column. The appendages are fleshy, pale purplish or yellowish white and laterally compressed with a circinnately recurved hollow corsal spur at base and two short obtuse obliquely divergent cuticles towards the top just below the apex. Anthers short, broad, somewhat horny with broadly triangular membranous anther tips that are inflexed over the sides of the stigmatic hood. Root Bark : The tap roots were found to be having prominent tops with rounded head and rest of the portion spirally curved. These hard roots are greyish white in colour and exhibit sap exudations at the places where bark has been cut. The bark of the older roots is cracked at places. The bark is yellowish grey outside and yellowish white inside. The upper cork portion is spongy and rough while the inner portion of bark is smooth and mucilaginous. The dried bark is bitter to taste. (Israili and Issar, 1977). Microscopical characters : Stem: (I) Epidermis:- This is an outermost layer of uniseriate cells with thick cuticle. Uni- and multicellular hairs cloth epidermis almost completely. Cells are barrel to rectangular and are compactly arranged. (II) Cortex:- These form a few layers below the epidermis which are collenchymatous. A few chloroplasts may also occur in these cells. Rest of the cortex is parenchymatous. Intercellular spaces are numerous. (III) Endodermis:- This layer of uniseriate cells forms a wavy ring around the vascular tissue, separates cortex from underlying tissues. The cells are barrel- rectangular shaped and are compactly arranged. Characteristic casparian thickening is lacking. It, however, contains starch grains and hence termed as starch sheath. (IV) Pericycle:- It is in the form of small patches of sclerenchymatous fibres. A few parenchymatous cells of the original pericycle are present between these groups. (V) Vascular tissue system: - Secondary growth is prominent. It shows groups of primary phloem, secondary phloem, cambium, secondary xylem, primary xylem and intraxylary phloem. Primary phloem is completely obliterated. Patches of secondary phloem occur above and close to the cambium. Cambium is unistratose. Secondary xylem forms a broad and extensive region. It comprises vessels and tracheids. The annual rings are feeble. Primary xylem occurs near the pith and is endarch. A few groups of phloem are situated just below the primary xylem in the region of pith and are the groups of intraxylary or internal phloem. (VI) Pith :- Centre is occupied by thin walled parenchyma and also many latex vessels. (VII) Points of ecological interest- A well differentiated cortex, presence of conjoint, bicollateral, open and endarch vascular bundles are characteristic feature. Intraxylary phloem which is primary phloem of the bicollateral vascular bundle is characteristic. It also shows the following xerophytic characters –(i) clothing of hairs (ii) thick cuticle (iii) collenchyma forming mechanical tissue (iv) chloroplasts in collenchyma and parenchyma of the cortex (v) sclerenchymatous pericycle and (vi) presence of numerous latex vessels in the pith. Chemistry The latex which is present in all parts of the plant contains water and water soluble matter 86.0-95.5% and caoutchouc 0.6-1.0 per cent. The latex of Calotropis procera is reported to contain cardiac steroid glucosides (Anonymous, 1956). Benzoyllineoline and Benzoylisolineolone were isolated from the root bark and on saponification gave lineoline and isolineoline; digitanols were also reported (Anonymous, 1952) The stem bark contains d- and –calotropeols, -amyrin, gigasnteol, a colourless wax, small amounts of tetracyclic terpene and traces of sterols. The flowers contained esters of -calotropeols, -amyrin, volatile and long chain fatty acids, esters of waxy acids and alcohols.