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ARACEAE(Arum family)
This large family contains about 2000 species in 115 genera. Although some species are natives of temperate regions, the vast majority are to be found in the tropics. They vary in habit from herbs large and small, to climbing shrubs and epiphytes, and include marsh plants and one floating water plant. The cuckoo pint (Arum maculatum L.) is a common woodland plant in Britain and Europe. Other species of Arum L. are cultivated as house and greenhouse plants. Among the more popular of the tropical species grown as house plants and decorative objects in hotel lobbies and such places are species of Alocasia G.Don, Anthurium Schott, Arisaema Mart., Caladium Vent., Colocasia Schott, Monstera Schott, Philodendron Schott, and Zantedeschia Spreng.. Many plants in this family contain a poisonous watery juice which may be rendered non-toxic by heat. The rhizomes of many species contain a large quantity of starch and are used as food after suitable preparation. Colocasia esculenta Schott (syn. Colocasia antiquorum Schott), Cyrtosperma edule Schott (syn. Cyrtosperma merkusii Schott), as well as species of Alocasia, Arum, and Caladium are of value. Many, but not all, species in this family contain bundles of minute needle-like crystals of calcium oxalate (known as raphides). They are responsible at least in part for the irritant properties of these plants when they are damaged and brought into contact with the skin or mucous membranes. The presence of other irritant compounds is also suspected - a proteinase has been demonstrated to occur in Dieffenbachia Schott species. Contact sensitivity to some of the species grown as house plants has also been recorded. The rhizome of the sweet flag contains a pleasantly aromatic oil. The rhizome and its oil have been used in the indigenous medicine of many countries for millenia (Flückiger & Hanbury 1874), and were accepted in western medicine until recently when their use in foods and cosmetics was prohibited by the FDA following long term feeding studies in rats which demonstrated carcinogenicity (Opdyke 1977). The aromatic oil may be extracted from the rhizomes by steam distillation, and is known as calamus oil. Bath preparations containing calamus oil have been reported to cause skin erythema; the oil has also been suspected of causing dermatitis in hypersensitive individuals (Klarmann 1958, Opdyke 1977). However, tests with undiluted calamus oil on the skin of mice, swine, rabbits, and guinea pigs did not demonstrate irritancy. A 48 hour closed patch test on human skin using 4% calamus oil in petrolatum similarly failed to demonstrate irritancy, and a maximisation test on 23 volunteers using this preparation failed to demonstrate a sensitising capacity. Phototoxicity following application of the undiluted oil to the skin of mice and swine was also not observed (Opdyke 1977). About 50 species have been recorded from Indo-Malaysia. The caustic effect of the leaves of some species when used in folk medicine was recorded by Burkill (1935).
These plants contain minute needle-like crystals of calcium oxalate which are intensely irritating when brought into contact with the mucous membranes of the mouth, nose, and throat, or with tender skin (Souder 1963). [Information available but not yet included in database] Members of this genus are irritant on account of their high content of needle-like calcium oxalate crystals (Burkill 1935), although the sap of these plants has also been described as having a severe stinging effect on bare skin (von Reis Altschul 1973). Several species are cultivated under the collective name of elephant's ears, referring to the shape of the leaves, but the term is also used for species of Begonia L. (fam. Begoniaceae).
These species have been recorded as being irritant (Burkill 1935, Souder 1963). This species has been recorded as being irritant (Burkill 1935, Uphof 1959). Perry & Metzger (1980) note that the species has been used as an irritant in dart poison and is also a contact poison since if the powdered plant is mixed with bamboo hairs and rubbed over the body, severe itching and sometimes death may occur. This species has been recorded as being irritant (Souder 1963). The rhizome may be used as a rubefacient (Perry & Metzger 1980).
The young plant appears to be relatively innocuous but the mature plant can cause severe dermatitis, apparently because of its content of calcium oxalate raphides as well as unknown poison. Chewing any part of the plant causes swelling of the lips and tongue, and merely to touch the lips after handling the plant is painful. Eating a leaf has caused the death of a child through suffocation through swelling of the throat (Cleland 1914, Cleland & Lee 1963). The whole plant is irritant; the sap of the leaves and petioles will blister the lips (MacPherson 1929) and is powerfully and sometimes destructively irritant to the eyes (Everist 1972, Arnold 1968, Francis & Southcott 1967, Souder 1963, Hurst 1942). The sliced tubers and leaves may be used as a rubefacient, and the acrid juice has been used to combat the caustic effect of the sap of Melanorrhoea laccifera Pierre (see Gluta laccifera Ding Hou, fam. Anacardiaceae) (Perry & Metzger 1980). von Reis Altschul (1973) refers to a plant thought to be Schizocasia portei as having irritant juice. The tubers contain abundant calcium oxalate raphides which are less abundant in those varieties cultivated for food use (Burkill 1935), but which can nevertheless cause pruritus, erythema, and whealing in those who handle them. Chewing the raw tuber may cause a burning sensation in the mouth, and urticaria may develop later. An acrid, irritant juice is present in the tubers which may be rendered harmless by thorough washing and boiling (Nadkarni 1976). Both the seeds and the tubers have been used as counter-irritants (Behl et al. 1966). This species is reported to irritate the oral cavity when eaten (Burkill 1935).
The sap of the flower produces marked itching (von Reis Altschul 1973). The fruit causes a lasting burning of the tongue and lips together with salivation and numbness. In Indian indigenous medicine, the crushed seeds are applied externally to bruises and also into cavities in teeth as an analgesic (Nadkarni 1976). The tubers of this species are considered to be inedible except in Java where they are eaten after suitable preparation (Burkill 1935). The genus has been classified by Engler in the sub-family Pothoideae which is characterised by possessing neither latex nor raphides of calcium oxalate (Willis 1973). However, this is contradicted by other publications that describe an unusual phenomenon, which is widespread among aroids, namely the presence of raphide crystals associated with pollen. The following is a representative list of Anthurium species reported by Barabé et al. (2004) to yield pollen mixed with calcium oxalate raphides:
The dermatological significance of these calcium oxalate raphides remains to be established. Souder (1963) included this species in a list of aroids containing microscopic stinging crystals of calcium oxalate. This plant is listed as irritant by Pammel (1911).
[Information available but not yet included in database] The genus contains about 150 species. Lewis & Elvin-Lewis (1977) note that the plants, and in particular the rhizomes, are poisonous on ingestion. The rhizomes contain abundant irritating calcium oxalate crystals but are edible if suitably prepared (Burkill 1935).
Both plants are irritant (Burkill 1935). The juice from the tubers is applied to the skin by the Khasi and Garo tribes of Meghalaya, India in the treatment of ringworm and other skin diseases (Rao 1981).
The plants are irritant but their roots also have a numbing effect on the skin and were used in China as ingredients of a local anaesthetic preparation applied to abscesses before these were opened surgically (Maxwell 1929). The tuber is said to be violently irritant (Behl et al. 1966). The common name cobra lily is also used for Darlingtonia californica Torr. (fam. Sarraceniaceae). The rhizomes are said to be particularly irritant (Kingsbury 1964). This species is described as being violently irritant (Behl et al. 1966).
The fresh juice of Arum triphyllum may cause vesication if applied to the skin (MacPherson 1929). Muenscher (1951), McCord (1962), Kingsbury (1964), and Hardin & Arena (1974) also referred to the irritancy of the leaves and tubers. Wren (1975) stated that the root has a burning and acrid taste. An ointment made by stewing the fresh corm with lard has been beneficially employed for ringworm (MacPherson 1929). The irritant effects of this plant have been known for centuries. Ramazzini's account of genital dermatitis in an apothecary appears to have been plagiarised from Dioscorides (Mitchell 1974b). The 15 species in this genus are found naturally in Europe. It is probable that all species contain an acrid and irritant poison as well as calcium oxalate raphides (MacPherson 1929). The sap causes dermatitis (Lampe & Fagerström 1968). Many plants previously named Arum are now placed in other genera; many plants in other genera of the Araceae are popularly known as arums. The sap contains crystals of calcium oxalate and is acutely irritant to the skin and to the mouth if chewed (Francis & Southcott 1967). The starch prepared from the tubers and named Portland arrowroot was formerly used as food (Prime 1960). The poisonous principle is destroyed by cooking. Gerarde (1636), who referred to the plant as Arum vulgare, stated that "The most pure and white starch is made of the roots of Cuckow-pint; but most hurtfull to the hands of the Laundresse that hath the handling of it, for it choppeth, blistereth, and maketh the hands rough and rugged, and withall smarting." Parkinson (1640), referring to the "common wake robin without spots", which he distinguished from the "spotted wake robin", noted that " […] when the leaves beginne to spring yeeldeth a milky sappe being broken or cut: the whole plant is of a very sharpe and biting taste, pricking the tongue upon the tasting, no lesse than Netles doe the hands, and so abideth for a great while without alteration; the roote with the sharpenesse hath a very strange clamminesse in it, stiffening linnen, or any other thing whereon it is laid, no lesse than starch : and in former dayes, when the making of our ordinary starch (which is made of the branne of wheate) was not knowen, or frequent in use, the finest dames used the rootes hereof, to starch their linnen, which would so sting, exasperate and choppe the skinne of their servants hands that used it, that they could scarse get them smooth and whole with all the nointing they could doe, before they should use it againe." He noted also that the spotted wake robin is "more sharpe and fierce than [the common wake robin without spots]." The acrid juice may cause dermatitis (North 1967) and also swelling of the tongue on contact, the dried plant being somewhat less irritant than the fresh material (Flück & Jaspersen-Schib 1976). The roots and berries have poisoned children in Europe (Lewis & Elvin-Lewis 1977).
There are 12 species, which are natives of tropical South America, and numerous named cultivars. Many have decorative foliage and are widely grown as house plants (Mabberley 2017). They are often incorrectly called colocasias (Lampe & Fagerström 1968).
Morton (1962a) noted that all parts of these plants but particularly the leaves and bulb, when raw, contain irritant crystals of calcium oxalate. When cooked, both the leaves and bulbs have been eaten as vegetables in tropical America and the West Indies. Souder (1963) included Caladium bicolor in a list of aroids described as containing microscopic stinging crystals of calcium oxalate that are intensely irritating when brought in contact with mucous membranes of the mouth, nose and throat, even in contact with tender skin.
Morton (1962a) noted that all parts of these plants but particularly the leaves and bulb, when raw, contain irritant crystals of calcium oxalate. When cooked, both the leaves and bulbs have been eaten as vegetables in tropical America and the West Indies. This species is a native of northern temperate and sub-arctic regions. The genus is monotypic. The plant, particularly its rhizome, is irritant (Kingsbury 1964) and poisonous on ingestion (Lewis & Elvin-Lewis 1977). Calla lily is a common name for Zantedeschia aethiopica Spreng. (syn. Richardia africana Kunth).
The tubers of this plant form a valuable food crop widely known as taro. They do, however, contain needle-like raphides of calcium oxalate in the superficial tissues, which can be removed by peeling. This may lead to irritation of the hands, the risk being lessened by peeling underwater (Burkill 1935). Calcium oxalate raphides are also present in the leaves and stems (Nadkarni 1976). Ingestion of any part of the plant in the raw state causes great pain and swelling of the lips, tongue, and throat (Dahlgren & Standley 1944, Williamson 1955, Souder 1963, Francis & Southcott 1967, Arnold 1968). The juice of this plant produced a positive patch test reaction in 2 of 53 patients who had hand dermatitis suspected to have been caused by vegetables (Sinha et al. 1977). Nadkarni (1976) notes that the juice of the petioles is rubefacient. The sap of the stems irritates the skin (Williamson 1955). The raw tuber is irritant to the skin and to the mucous membrane of the mouth (Souder 1963).
There are about 30 species, natives of tropical America and the West Indies. Certain species are widely cultivated for their decorative foliage, being commonly seen in hotel lobbies, waiting rooms, restaurants, and such places. Contact with the bruised or broken plant material may cause severe blistering and inflammation of the skin (Delph 1937, Dahlgren & Standley 1944, Occhioni & Rizzini 1958, Barnes & Fox 1955). All species contain calcium oxalate raphides (Souder 1963), but their irritant effect on skin and mucous membranes are believed to be increased by the presence of other substances (Manno et al. 1967, Fochtman et al. 1969, Walter & Khanna 1972). However, not all species have an irritant sap (Arnold 1968).
These species are said to be irritant (Allen 1943). The name Dieffenbachia exotica is of no botanical standing but is nevertheless used in the USA and Canada. Tests on rabbit eyes showed mild irritation with the juice of this plant (Manno et al. 1967, Fochtman et al. 1969). Irritation of the hands is produced by raphides of calcium oxalate when split portions of this plant are handled (von Reis Altschul 1973).
If the stem is bitten, the resulting bullous stomatitis is of such severity that it renders the victim speechless (Francis & Southcott 1967). There may also be oedema of the skin around the mouth. Similar reactions have been reported to both species (Burkill 1935, Drach & Maloney 1963, Behl et al. 1966, Everist 1972, Faivre et al. 1974). Sporadic cases of severe stomatitis caused by these plants continue to be reported (Jaspersen-Schib et al. 1996). Experiments in rats have shown that pretreatment with antihistamines affords some protection against the effects of the juice on the oral cavity, but treatment with cortisone merely delays the reaction (Fochtman et al. 1969). Piffard (1881), referring to Caladium seguinum, noted that the juice of the leaves when applied to the skin produces intense itching and burning, and afterwards inflammation. Brache & Aquino (1978), referring to Dieffenbachia maculata, report that this species is among the 14 commoner causes of plant dermatitis in the Dominican Republic (where the plant is known as matapuerco or brazo ponderoso). Burkill (1935) and von Reis Altschul (1973) also report that the juice of D. seguine irritates the skin. Tests on rabbit eyes have shown severe irritation with the juice of D. picta (Manno et al. 1967, Fochtman et al. 1969), the toxicity being associated with a labile protein-like substance present in the sap. Walter & Khanna (1972) have isolated a proteinase, named dumbcain, from Dieffenbachia amoena, Dieffenbachia picta and Dieffenbachia seguine, and consider that the irritant activity of these species could arise from the intradermal injection of the proteinase by the calcium oxalate raphides present in the plants. Lynne-Davies & Mitchell (1974) applied portions of the fresh leaf from Dieffenbachia amoena to the backs of 2 males for 48 hours under occlusion. Neither irritant reactions nor delayed flares occurred. The calcium oxalate raphides of Dieffenbachia picta leaves are present in two size ranges. The smaller raphides measure 10–20 µm in length and a little under 1 µm in diameter, and are contained within typical idioblast cells. The larger raphides measure 130–150 µm in length and about 3 µm in diameter, are sharply pointed at both ends, and are contained in unusual, randomly scattered capsular cells from which they may be expelled through the ends (Schmidt RJ 1981 — unpublished observation).
This is the Drakontium of Hippocrates. The root is irritant (Watt & Breyer-Brandwijk 1962).
The juice is irritant and a frequent cause of dermatitis. Florida nurserymen who cut up stems for propagation commonly complain of "pothos poisoning". Contact with the sap can cause dermatitis (Hardin & Arena 1974, Morton 1971) and biting into the stem has caused irritation of the mouth and tongue (Morton 1962a, 1971). The plants contain needle-sharp raphides of calcium oxalate (Souder 1963). A case of allergic contact dermatitis caused by Scindapsus aureus in a florist was reported by Mobacken (1975). A papulovesicular patch test reaction was produced by the leaf; control tests in 21 volunteers were negative. The patient did not react when patch tested with the leaf of an unnamed Dieffenbachia species. This species is reported to be irritant. The liquid contained in the spathe of the flowers is very irritating. When the fruit decays, bast cells and needle-shaped crystals are liberated. Malays are reluctant to touch the fruit as the irritant dust may cause blindness (Gimlette 1929). The rhizomes of some species are slightly irritant (Burkill 1935). This genus of 50 species of climbers and epiphytes occurs in the West Indies and Tropical America. According to Allen (1943), the juice of all species is acrid and caustic, causing a painful burning on contact with the skin.
This taxon may be found in the trade as "Philodendron friedrichsthalii", a name of no botanical standing. This species is reported to be irritant (Souder 1963). Hammershøy & Verdich (1980) observed positive [cross- ?]reactions to the crushed leaf and the crushed stem of Monstera friedrichsthalii in one of four patients being investigated for contact sensitivity to Philodendron scandens subsp. oxycardium (Schott) G.S.Bunting [see below]. An ether extract of leaves and stems produced no reaction.
This climbing plant is very widely grown. The unripe fruit is acrid, but becoming edible when ripe. Dahlgren & Standley (1944) caution that the unripe fruit contains needle-like crystals that irritate the mouth. Irritation of the throat may develop if all remains of the flower are not removed (Burkill 1935), and the fruit may cause allergy or anaphylaxis in the form of a rapidly developing and extensive urticaria (MacPherson 1929, Francis & Southcott 1967). The spadix is also edible (Hurst 1942). Hammershøy & Verdich (1980) observed positive [cross- ?]reactions to the crushed stem of two plants identified by their supplier as "Philodendron monstera" and as "Philodendron perthusum" [names of no botanical standing] in one of four patients being investigated for contact sensitivity to Philodendron scandens subsp. oxycardium (Schott) G.S.Bunting [see below]. Neither the crushed leaves nor an ether extract of leaves and stems produced a reaction.
These species are reported to be irritant (Souder 1963). This species is named for the irritant cells formed abundantly in the apex of the gynoecia as the fruits ripen (Simmonds 1950). The abundant sap of this plant has caused dermatitis in labourers cutting it with a machete. Erythema develops immediately on contact with the sap and fades in 24–72 hours (Dao 1967). Recognised by Willis (1973) as comprising 275 species of shrubs, climbers, and epiphytes, Plants of the World Onlinea now lists 621 accepted species. It is the second largest aroid genus after Anthurium Schott. They are found in tropical and sub-tropical America and in the West Indies. Several species are popular as foliage house plants in temperate regions (Hunt 1968/70), Mabberley (2017) noting that Philodendron bipinnatifidum Schott ex Endl. was the most familiar, and that Philodendron hederaceum (Jacq.) Schott was probably the the most common house plant in the world. However, many more species, hybrids, and cultivars can be found being offered for sale in the horticultural trade.b,c,d Whilst a facility is now provided by the International Aroid Society as the International Cultivar Registration Authoritye to register aroid cultivar names, most Philodendron cultivars have for one reason or another not been registered. West & Miller (1956) described the then known species and hybrids (of which there nine) found in the trade, and provided drawings comparing the many leaf shapes of these foliage plants. More recently, an overview of the history of hybridisation within the genus has been provided by Devanand et al. (2004) who carried out phylogenetic studies on 43 cultivars across 15 species to look for relationships indicative of parentage. Their study revealed a good deal of confusion: cultivars with the same name were genetically different; other cultivars had seemingly been mis-labelled; and species names were being used as cultivar names. This erratic nomenclature of the florists has in turn been copied into medical reports. Ayres & Ayres (1958) reported 12 cases of dermatitis to various but not rigorously identified species of Philodendron. Conjunctivitis from contact and stomatitis from ingestion have also been noted (Everist 1972). Some species are irritant, and some can sensitise. Hjorth (1966a) observed no positive patch test reactions in 93 patients tested over a period of six years with an unidentified philodendron. Dermatitis from a Philodendron was reported by Zina & Bonu (1960). The patient also showed a positive patch test reaction to Primula L. (fam. Primulaceae) flowers and leaves.
This plant contains intensely irritating crystals of calcium oxalate (Souder 1963). Philodendron selloum is reported to have caused dermatitis (Ayres & Ayres 1958). Pardo-Castello (1923), later cited by Weber (1930), included this taxon in a list of tropical plants producing contact dermatitis. Engel & Horn (1972) provided a case report of a phytodermatosis caused by Phyllodendron consanguineum [sic]. This species is particularly favoured as a house plant. Ayres & Ayres (1958) reported several cases of strongly positive and very persistent delayed allergic contact reactions to this plant. Lewis & Elvin-Lewis (1977) state that the leaf juice from this species, after mixing with soap, has been used in Brazil to treat eczema.
Souder (1963) included Philodendron hastatum in a list of aroids on Guam that contain microscopic stinging crystals of calcium oxalate, which can be intensely irritating to mucous membranes of the mouth, nose, and throat, or tender skin.
[Information available but not yet included in database]
A common indoor pot-plant identified as Philodendron Scandens cardatum [sic] but now recognised as Philodendron scandens subsp. oxycardium caused dermatitis of the face, neck, hands, and arms in a commercial greenhouse worker (Dorsey 1958). A patch test with wet crushed stem and leaf was positive. Dermatitis was said to be not uncommon in commercial nursery workers. Earlier, Harris (1942) had reported dermatitis of the eyelids in a housewife from the same mis-named taxon. Allergic contact sensitivity to this taxon in four patients has been described by Hammershøy & Verdich (1980). Positive patch test reactions to the leaves, stem, and ether extract were observed. Cross sensitivity was observed in the various patients to Philodendron tuxtlanum Bunting, Monstera friedrichsthalii Schott, and to various Monstera deliciosa Liebm. cultivars, but not to Philodendron bipinnatifidum Schott. These plant contains calcium oxalate raphides (Souder 1963). Hammershøy & Verdich (1980) observed positive [cross- ?]reactions to the crushed leaves and crushed stem of this cultivar in two of four patients being investigated for contact sensitivity to Philodendron scandens subsp. oxycardium (Schott) G.S.Bunting [see above]. Lynne-Davies & Mitchell (1974) applied portions of the fresh leaf of this cultivar to the backs of 2 males for 48 hours under occlusion. Neither irritant reactions nor delayed flares occurred.
This taxon may be found in the trade as "Philodendron tuxla", a name of no botanical standing. Hammershøy & Verdich (1980) observed a positive [cross- ?]reaction to the crushed leaf of Philodendron tuxtlanum in one of four patients being investigated for contact sensitivity to Philodendron scandens subsp. oxycardium (Schott) G.S.Bunting [see above]. Neither the crushed stem nor an ether extract of leaves and stems produced a reaction. This species is reported to be irritant (Pammel 1911). Contact dermatitis caused by this species has been reported (Ayres & Ayres 1958). The fresh tuber contains a substance that is strongly irritating (Pammel 1911), and when eaten causes pharyngeal swelling which persists for several days (Kariyone 1971). In traditional Chinese medicine, the dried tuber is known as ban xia or pan hsia. Stuart (1911), referring to Pinellia tuberifera, notes that the viscid sap of the stalk of the plant is said to restore fallen hair and whiskers. Huang (1993), referring to Pinellia ternata, states that the plant is applied externally to wounds to obtain a hemostatic and analgesic effect. The 75 species are natives of Madagascar and Indo-Malaysia, but are cultivated elsewhere in the tropics. Pothos is used as a common name for some plants in other genera, particularly Anthurium and Scindapsus Schott species. Therefore, reports of dermatitis unsupported by reliable botanical identification should be accepted with scepticism (Kelsey & Dayton 1942). According to Arnold (1972), these plants are the commonest cause of dermatitis in Hawai‘i, except during the fruiting season of the mango (Mangifera indica L., fam. Anacardiaceae) when the latter predominates. The genus Pothos has been classified by Engler in the sub-family Pothoideae, which is characterised by possessing neither latex nor raphides of calcium oxalate (Willis 1973). According to Burkill (1935), the leaves of this species have been used by the Malays as an external medicine applied to the abdomens of small children to cause expulsion of worms. This commonly grown house plant is highly irritant. It is occasionally called Arum cornutum, a name of no botanical standing. The term voodoo lily is also applied to species of Arisaema. Souder (1963), referring to the white anthurium Spathiphyllum cv. Clevelandii, states that this plant contains intensely irritating calcium oxalate crystals. [Information available but not yet included in database]
The single species in this genus is occasionally cultivated as a bog plant, but occurs naturally in north-east Asia, Japan, and Atlantic North America. Bigelow (1817) stated that an acrid principle exists in the roots even when perfectly dry. Cheney informed White (1887) that the root produces intolerable itching and inflammation of the skin. According to Wren (1975), the taste of the root is acrid and biting. The irritant properties, particularly of the root, are noted by Weber (1937), Lampe & Fagerström (1968), and Kingsbury (1964). Lysichitum americanum Hultén & St. John is also known as skunk cabbage. The plant contains irritating crystals of calcium oxalate (Souder 1963). von Reis Altschul (1973) records that this species is very poisonous.
The rhizomes of these two species are acrid (MacPherson 1929). This species contains irritating crystals of calcium oxalate (Souder 1963). The tuber of this species is rubefacient (Perry & Metzger 1980). The tuber is very irritant (Burkill 1935). The roots are edible, but poisonous unless repeatedly boiled and the water discarded (Wild 1961). See also Xanthosoma below. Of the 38–40 species, all indigenous to the American tropics, some are valued as food plants, particularly as dietary sources of starch. X. caracu K.Koch & C.D.Bouché, X. atrovirens K.Koch & C.D.Bouché, and X. nigrum Mansf. would appear to be the most important in this respect. They are known by a wide variety of local names, but the general adoption of the term cocoyams has been advocated in the interests of simplicity (Morton 1972a). All parts of the plants contain, to a varying degree, calcium oxalate raphides which can cause dermal, oral, and intestinal irritation, but which are wholly or largely destroyed by cooking. In addition, poisonous water-soluble materials may be present; these are released into the cooking water on boiling (Morton 1972a).
The leaves of this species are irritating unless scalded (von Reis Altschul 1973). The tubers are non-acrid and edible, but tiny (Morton 1972a).
The plant has acrid milky sap and a foetid odour. In Surinam, the small lateral tubers and the leaves are cooked and eaten. In the Andes of southern Colombia, the tubers are ground, boiled, and fermented to make chicha, an intoxicating drink (Morton 1972a).
The rhizome, tubers, young leaves, and petioles are widely used for food in tropical America, Africa, and Asia (Morton 1972a). Dahlgren & Standley (1944) caution that the raw roots and leaves of Xanthosoma violaceum contain crystals which will irritate the mouth and throat. Souder (1963) notes the presence of irritant calcium oxalate crystals in this species. According to Burkill (1935), a variety of this species having streaked leaf stalks was particularly irritant to the mouth. The tuber of this species is edible after cooking, but immediate severe irritation of the mouth and throat occurs if fresh material is eaten (Sakai et al. 1972). Specialised cells containing calcium oxalate raphides occur in all parts of the plant. A microscopical study of these raphides has revealed that they are barbed and grooved (Sakai et al. 1972). Morton (1972a) notes that various authors have applied the binomial Xanthosoma sagittifolium loosely to any Xanthosoma species being cultivated for their so-called "roots".
This plant, a native of southern Africa, is naturalised in parts of Australia and is widely cultivated elsewhere, including Europe and North America. Johnson (1897) reported that laundresses at Funchal, Madeira who tried to utilise the starch obtainable from the corms of Richardia aethiopica, suffered irritation of the hands which, upon investigation, was found to have been caused by numerous needle-shaped raphides. Eating the plant causes swelling of the lips, tongue, and pharynx, and gastrointestinal irritation (Everist 1962). References
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