This large family of erect and twining shrubs and perennial herbs consists of 130 genera and some 2000 species. The plants are fairly widely distributed in the tropics and subtropics, but rare elsewhere.
Some species may be found in collections of succulent plants, for example Hoya R.Br. and Stapelia L. species; some are grown in temperate climates as border plants, for example Asclepias L. species; others are cultivated for their fibre, local medicinal use, etc.
The leaves of Gymnema sylvestre R.Br. contain gymnemic acid, the term used to describe a mixture of triterpenoid saponins of closely related structure, which has the capacity to obtund taste for several hours for sweet, but not bitter, sour, astringent, nor pungent substances (Webb 1948a, Dateo & Long 1973).
Tylophorine and related alkaloids present in Tylophora R.Br. species have long been known to be vesicant. Many other species are noted for their alkaloid, saponin, cardiac glycoside, or proteinase content. Although several species have been described as being dermatitic, the nature of the compounds responsible is generally unknown. It is probable that irritancy or allergenicity is a far more common property of this family than the available literature suggests. Several species of Dischidia R.Br., when growing in their natural habitat in Far Eastern rain forests, are hazardous to handle because of their myrmecophilous nature.
The latex has been found to produce a slightly painful oedematous swelling on application to the shaven ear of the rabbit. A serum-like fluid exudes on the surface of the swollen area and forms a yellowish scab which persists for some time. The latex has also been used as a local application to warts (Watt & Breyer-Brandwijk 1962). Bull & Burrill (2002) also refer to the skin irritant properties of the milky sap.
The common names of this plant refer to the property that the flowers have of trapping pollinating insects. Because of this, the plant is sometimes erroneously described as insectivorous.
There are about 120 species, most of which are natives of the Americas, particularly the USA. Some are widely cultivated in Europe as border plants.
The plants contain cardiac glycosides which render them poisonous on ingestion (Lewis & Elvin-Lewis 1977). Several species have been found to contain proteinases in their latex.
The latex is employed by Nevada Indians to treat ringworm (Train et al. 1957).
The plant's milky latex will produce dermatitis in susceptible individuals (Allen 1943, Blohm 1962).
Asclepiodora viridis is listed by Shelmire (1940) as being able to produce dermatitis.
The latex is applied by Nevada Indians to remove corns and callouses (Train et al. 1957).
Carpenter & Lovelace (1943) purified a proteinase, named asclepain, from the roots of this species. Lynn et al. (1980) demonstrated that the asclepain from this species consists of two series of compounds each consisting of five separate proteinases which they named asclepain A1, A2, A3, A4, & A5 and asclepain B1, B2, B3, B4, & B5.
The powdered root, when applied to the skin, is escharotic (Piffard 1881).
This species, and Calotropis procera W.T.Aiton, provides the crown flowers of Hawaiian "leis" and in this capacity can be violently irritant (Arnold 1968). In contact with the eye, the latex causes severe irritation, a burning sensation, swelling of the eyelids, and blurring of vision from corneal oedema (Muthayya 1948, Wong 1949, Crawford 1958, Sugiki 1966, Duke-Elder & MacFaul 1972b). Recovery is spontaneous and complete, requiring no specific treatment (Grant 1974). The latex is irritant, caustic, and depilatory when applied to the skin (Behl et al. 1966, Morton 1962, Blohm 1962, Nadkarni 1976).
Nadkarni (1976) describes how various parts of this plant are used in Indian traditional medicine in the preparation of remedies for the treatment of skin diseases. For example, the root bark reduced to a paste with sour congee (rice vinegar) is applied to elephantiasis of the legs and scrotum; a powder of the dried leaves is dusted on wounds and ulcers to destroy excessive granulation; and the milky juice is used for ringworm of the scalp, to destroy piles, and applied to ulcers to hasten healing.
As well as containing calotropin and other cardiac glycosides, the latex contains several proteinases. Abraham & Joshi (1979a, 1979b) describe two carbohydrate-containing proteinases, calotropain FI and FII, the former being very similar in its properties to chymopapain, whilst the latter more closely resembles papain. Pal & Sinha (1980) also describe the isolation of two other papain-like proteinases, calotropains DI and DII that do not contain carbohydrate, and the detection of a further three proteolytic enzymes.
The plant may be found in cultivation for the strong fibre from its bark, and the silky hairs from its seeds.
Morton (1962a) asserted that the milky sap is caustic and irritant on skin, and may cause swelling and ulceration. The milky juice has also been described as rubefacient by Irvine (1961), and as a depilatory by Morton (1962a). Singh et al. (1978) observed irritant effects in all six contact dermatitis patients patch tested with the leaf crushed in normal saline. Williamson (1955) also reports the caustic nature of the plant.
According to Wren (1975), the bark is used as a local remedy in India for elephantiasis, leprosy and chronic eczema. Nadkarni (1976) records that the medicinal properties of the plant are similar to those of Calotropis gigantea, and that the milky juice (latex) has been used as a blistering agent.
Its use in India in the treatment of skin diseases has caused severe bullous dermatitis leading sometimes to hypertrophic scars (Behl et al. 1966). The local effect of the latex on the conjunctiva is congestion, epiphora, and local anaesthesia. It has occasionally been used to produce such symptoms by malingerers (Dalziel 1937).
The latex of this species is similar to that of Calotropis gigantea in its content of proteinase and also calotropin and other cardiac glycosides (Watt & Breyer-Brandwijk 1962). Atal & Sethi (1962) isolated calotropain from the latex and showed it to be a mixture of at least five proteinases. The proteolytic activity of calotropain was greater than that of papain, ficin, or bromelain.
Nadkarni (1976) notes that the leaves of this woody climber are used in Indian traditional medicine to cure ulcerous sores.
Several species growing epiphytically in their natural habitat are characteristically associated with "ant-gardens". If handled, the disturbance of these ant-gardens renders the intruder liable to attack by a swarm of ants; a pseudophytodermatitis caused by the bites and/or stings of these insects may be the outcome. The plants in such ant-plant relationships have been described as super-nettles. A review of this topic is provided by Schmidt (1985).
Menninger (1967) provides a photograph of this myrmecophyte.
Menninger (1967) provides a photograph of this myrmecophyte and of a section through one of its ant-inhabited "pitchers".
Nadkarni (1976) notes that in Indian traditional medicine a paste of the root is applied to cleanse and cure ulcers and swellings; also that the milky juice is dropped into inflamed eyes, causing copious lachrymation and afterwards a sense of coolness. The plant is also included in multi-ingredient medicines used to treat various chronic diseases of the skin.
The juice of this south-eastern European species blisters the skin (Howes 1974).
Stuart (1911), referring to Metaplexis stauntoni, notes that in Chinese traditional medicine, the plant is known as lo mo or huan lan. Its seeds when crushed are used as an astringent and haemostatic application to wounds and ulcers. They are also applied to all sorts of insect bites but are thought to have escharotic properties if used too frequently. Perry & Metzger (1980), referring to Metaplexis japonica, state that the crushed seeds may be caustic.
In Indian traditional medicine, a decoction of the plant is used as a gargle and mouthwash in the treatment of sore throat and aphthous ulcers (Nadkarni 1976).
Referring to Daemia extensa, Nadkarni (1976) notes that this twining plant is extremely irritant, but no further detail is given. He notes also that in Indian traditional medicine, the fresh leaves made into a pulp are used as a stimulating poultice for carbuncles; also the juice of the leaves is employed in the preparation of a medicinal oil used in rheumatism.
Nadkarni (1976) notes that the milky juice is used in traditional medicine for swellings.
This species has caustic sap (Hurst 1942, Webb 1948a) which blisters human skin (Everist 1972). The milky juice has been used to treat corns and warts, and has been used as a healing application to wounds (MacPherson 1932).
The plant is said to produce urticaria on contact with the skin (Watt & Breyer-Brandwijk 1962).
Ratnagiriswaran & Venkatachalam (1935) described how one of them was continuously affected with dermatitis during the extraction and isolation of the alkaloids from this plant, particularly with solutions of the alkaloids in ether, benzene, or chloroform. Eruptions appeared on the skin a day after exposure. Itching, subsequently erythema and oedema were experienced. The symptoms continued for a week then subsided. The alkaloids tylophorine and tylophorinine present in this species have since then often been described as vesicant (Govindachari et al. 1961, Gellert et al. 1962), but no formal skin testing appears to have been reported in the literature.
This species has been used in Indian medicine for the treatment of asthma and bronchitis, and as an expectorant (Nadkarni 1976).
Both of these species contain tylophorinine, the latter also containing tylophorine (Phillipson et al. 1974). These alkaloids have been described as vesicant (see Tylophora asthmatica above).
The skin vesicant action of this species has been described as less pronounced than that of Tylophora asthmatica (Gellert et al. 1962). It contains tylophorine and tylocrebrine (Phillipson et al. 1974).
The roots of Vincetoxicum officinale have been found to contain tylophorine (Pailer & Streicher 1965), an alkaloid that has been described as being vesicant (see Tylophora asthmatica above).