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Euphorbia lathyris L.

Euphorbiaceae

Mole plant, Petroleum plant, Caper spurge, Gopher plant

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Toxicity
  5. Description
  6. Germplasm
  7. Distribution
  8. Ecology
  9. Cultivation
  10. Harvesting
  11. Yields and Economics
  12. Energy
  13. Biotic Factors
  14. References

Uses

Sold, for example, by Maryland nurseries as the Mole Plant, this attractive poisonous evergreen perennial belongs to a family, many species of which are believed to repel moles. Castor bean is another Euphorbiaceous plant believed to repel moles and other subterranean pests. Recently (Science 194:46. 1976) Nobel Laureate Melvin Calvin has suggested that the mole plant could be the "petroleum plant", producing a hydrocarbon substance very much like gasoline. Calvin states that the hydrocarbon produced by the plant could probably be used directly in existing refineries, after it had been separated from the water. His estimates of 10 to 50 barrels of oil per acre per year seem optimistic as do his cost estimates of $3–10 per barrel. If these estimates prove to be correct, however, the petroleum plant would have virtues to outweigh its poisonous and weed properties. Assuming 50 barrels of oil per acre per year at a cost of $10 per barrel, a $15.00 sale price yields only $250 profit per acre. If Calvin's optimistic estimates are proven, the plant merits further attention. Guayule rubber has been estimated to give 6000 kg/ha latex equivalent to only about 10 barrels oil per hectare (4 barrels per acre). It is difficult to believe that Euphorbia lathyris would produce 10 times more latex than guayule. However the latex in Maryland-grown material is extremely copious. Calvin suggests that the plants could be simply cut down and run through a crushing mill, new plants growing from the stumps. He suggests that replanting would be necessary every 20 years or so. If he produced 40 barrels an acre, he estimates it would take an area the size of Arizona to meet our current gasoline requirements. Seeds are said to yield a fine clear oil known as oil of Euphorbia, obtained by expression or by ether or alcohol extraction. The latex is said to be depilatory. Uphof (1969) states that the seeds are used as a coffee substitute. They are poisonous! The oil has been used in soap manufacture.

Folk Medicine

French country folk are said to take 12–15 seeds as a purgative, perhaps similar in action and toxicity to castor oil. The root is equally purgative and emetic. The leaves, like the latex, are vesicant, and have been used by beggars to incite pity-producing blisters. According to Hartwell (1967–1971), the latex is used in folk remedies for cancers and warts. Reported to be antiseptic, cathartic, diuretic, emetic, POISON, and purgative, mole plant is a folk remedy for cancer, corns, diarrhea, gangrene, melanoma, skin ailments, sores, and sorethroats. Homeopathically the seeds are used for erysipelas, paralysis, and rheumatism. The seed oil is applied to burns.

Chemistry

The L isomer of dopa [3-(3, 4-dihydroxyphenyl) alanine] is said to occur at 1.7% of the fresh weight of the latex. L-dopa is used for symptomatic relief of Parkinson's disease, and is said to have produced some astounding rejuvenating effects, inducing priapism, on some senile males who took it. Leaves contain quercetin, quercetin-3-b-D-glucuronide, kaempferol, kaempferol 3- glucuronide, b-sitosterol, p-coumaric acid, and ferulic acid. Stalks contain hentriacontane, taraxerone, taraxerol, b-sitosterol, and betulin. The energy-promising latex contains 0.5% 3,4-dioxyphenylalanine. Sachs et al. (1981) got 6.2% rosin content (hydrocarbons) in nonirrigated, compared to 4.4% on irrigated plots. The benzene extract of the leaves is said to contain 0.1% (% of plant dry weight) rubber, and 0.2% wax; the acetone extract 13.7% glycerides, 2.2% isoprenoids, and 8.3% other terpinoids. The acetone extract of the seeds contains 40% glyceride. Per 100 g, the seed is reported to contain 15 g protein and 40–47.5 g fat. Seed contain b-sitosterol, 7-hentriacontane, and daphnetin (List and Horhammer, 1969). I predict that if all plants are studied in detail, they will be found to contain both carcinogens and antitumor or cytotoxic compounds. This one contains the antitumor compound b-sitosterol and the cocarcinogen ingenol-3- hexadecanic acid ester (C36H58O6).

Toxicity

According to Hager's Handbuch, human overdoses result in burning mouth, nausea, diarrhea, dilated pupils and collapse with pallor, rigidity, frigidity, cold sweats, arrhythmic pulse, vertigo, delirium, alternating hot and cold flashes, cramps, etc. (List and Horhammer, 1969–1979). The seeds are said to contain aesuletin, and an unnamed alkaloid and the seed oil is violent POISON. The plant has caused poisoning in children. Five California women are said to have pickled the fruits, believing them to be capers. Severe but not fatal poisoning ensued.

Description

Glabrous to glaucous succulent annual, biennial, perhaps perennial, to 1 m tall, simple or branching if disturbed (coppices readily if top pinched), with a copious white sticky latex. Leaves simple, entire, lanceolate, essentially one-nerved, opposite or whorled on the stem, narrowly lanceolate, apically acute, basally abruptly truncate, to 15 cm long. Leaves subtending flower clusters broader, shorter, the flowers greenish yellow. Fruits usually 3-lobed, subglobose, 1/2 to 1 cm long. Seeds ovoid, flattened, 4–6 mm long, carunculate, hard.

Germplasm

Reported from the Mediterranean Center of Diversity, mole plant, or cvs thereof, is reported to tolerate drought, frost, and poor soils. One might detect two schools of thought on the feasibility of the petroleum plant, the optimistic Calvin camp and the pessimistic Sachs school. Sachs et al. (1981) say, "The implication that genetic improvement will greatly increase rosin content is not well founded. We have no germplasm on hand for Euphorbia lathyris to suggest that we can go much beyond 5 to 6 percent hexane extractables... A recent world-wide search for new germplasm has not yet uncovered E. lathyris plants with significantly higher rosin contents." (2n = 20)

Distribution

Native of the Mediterranean, cultivated as medicinal or ornamental, escaping and self-seeding along the East and West coasts of the United States. Introduced for example in Santa Cruz Co. Arizona, "to repel rodents in an orchard".

Ecology

A hardy annual, biennial or perennial, self-seeding and overwintering in Maryland, with great potential as a weed, ignored by grazing animals. Ecologically the plant is estimated to range from Cool Temperate Dry to Wet through Warm Temperate Dry to Moist Forest Life Zones, areas with annual temperatures of 10 to 15°C, annual precipitation of 5 to 15 cm rainfall, tolerating very sterile soils.

Cultivation

In California, Sachs et al sowed at a rate of nearly 250,000 seed per ha, thinning to ca 80,000 or 150,000 or 190,000 plants per ha for their experimental studies. Weekly irrigation replaced evapotranspiration, so that there was little or no moisture deficit, except at the plot extremities. In most tropical climates where chilling below 10°C does not exceed 1,000 hours, year-round plantings are satisfactory and planting dates can be chosen to exploit rainfall or cropping rotation (Sachs et al., 1981). In greenhouse tests, germination as high as 90% after 5 days at 23°C was reported.

Harvesting

At Davis, drying the petroleum plant is more difficult than drying oil seeds. Plants harvested and left in early October were not dry enough for milling and hexane extraction by early November.

Yields and Economics

White et al. (1971) reported seed (or fruit) yields of more than 3 MT/ha from Beltsville (annual precipitation ca 10 dm, annual temperature ca 13°C). The seeds contain nearly 50% oil, suggesting a potential seed oil yield of 1.5 MT. In Sun Times (October, 1980) we read that Diamond Shamrock hopes to set 25 barrels of oil per acre from the latex. "Cost estimates for oil from gopherweed range from $20 to $60 a barrel, compared to the current oil world price of $32 a barrel." The bottom line, from an energy point of view, may rest nearer. Sachs et al. (1981) who conclude that hydrocarbons from Euphorbia lathyris would have to sell for $150 to $200 a barrel to be a practical source of fuel. They got lower yields with propotionately higher biocrude contents on their unirrigated plots. McLaughlin et al. (1982) report biomass yields of 14 MT/ha/yr with 8% biocrude for a biocrude yield of 8.6 barrels per hectare at a cost of $104/barrel ($31/GJ).

Energy

There is a bewildering array of reported yields for the petroleum plant, 22 MT DM/ha (Nemethy et al., 1980), 19.8–24.7 barrels/ha/yr (mentioned by Sachs et al., 1981), 16.3–19.3 MT DM/ha/yr (irrigated, Sachs et al., 1981), 10.3–14.7 MT DM/ha/yr (fertilizer tests, Sachs, et al., 1981), 20–25 barrels/ha/yr (Calvin, 1980). Calvin's early estimates of supplying gasoline sufficient to satisfy U.S. requirements by planting an area the size of Arizona to Euphorbia lathyris (40 barrels per acre). None of the estimates published in the 80's approach that yield. Sachs et al. (1981) realized yields were closer to 5 barrels per hectare, suggesting it might take 20 Arizona's not one, to satisfy U.S. petroleum needs, if planted to Euphorbia lathyris. According to Nemethy et al. (1980), the heptane extract has a low oxygen content and a heat value of 42 MJ/kg which is comparable to those of crude oil (44 MJ/kg). Perhaps they are also optimistic in suggesting that the potential Euphorbia lathyris yield is equal to that of sugar cane (11.7 x 104 MJ ha/yr) adding the oil yield (6.5) and the alcohol yield (5.2 x 104 MJ ha/yr). Still, in the Sun Times (October 1980, p. 15) an anonymous source says, "Melvin Calvin, Nobel laureate in chemistry, believes that the U.S. could produce more than 2 million barrels a day of gopheroll by 1985. The Department of Energy has granted Calvin $250,000 to continue his research. Marvin Bagby, head of the Agriculture Department's hydrocarbon-plant research project, thinks that gopherweed is the leader among forty-five hydrocarbon-bearing plants that have commercial promise. McLaughlin et al (1982) project a biocrude yield of 41.8 GJ with a bagasse yield of 216.4 GJ/ha/yr. Assuming a 300,000 MT/yr processing facility, the total energy requirements would be 1285 x 1012 J, the gross production of biocrude 895, the net electricity production 1343 for a total net energy production of 953 x 1012 J at a cost of $28/GJ or $104/bbl for the biocrude. The biocrude energy yield is exceeded by the energy requirements, but the bagasse yield more than compensates.

Biotic Factors

Some diseases listed under this species are: Melamspora euphorbiae-dulces, Phoma euphorbiphila, Pleospora herbarum, Sclerotium lathyris, Tithymalus leiococeus, Aecidium tithymali, and Melampsora monticola. Sachs et al. (1981) note in field plantings in California and Arizona, Pythium aphanidermatum and Pythium ultimum were identified as possible pathogens of Euphorbia lathyris, and pre- and post-emergence damping-off caused by Pythium spp. was believed to be important in limiting initial stands in some earlier California field trials. Greenhouse experiments were conducted to determine whether seed treatment fungicides at rates nontoxic to E. lathyris could satisfactorily control damping-off. The fungicide diazoben (Lesan), widely used as a seed treatment to control Oomycetes, was effective against P. aphanidermatum, P. ultimum, P. carolinum, or P. vexans at rates as low as 0.1 gram active ingredient per kg seed. Thus, all field plantings at Davis in 1980 were diazoben-treated seed. Another disease, unrelated to Pythium damping-off or root rot, occurred to some degree in each of the 1980 field plots. Affected plants had stunted, yellowed foliage, and main and lateral roots were blackened up into the crown and lower stem tissue. Microscopic examination showed the blackening to be large numbers of small, black sclerotia in the tissues. When affected tissues were cultured on potato dextrose agar, they consistently gave rise to the sclerotial state of Macrophomina pahseolina, which has also caused disease of E. lathyris in Arizona. Macrophomina phaseolina is a serious pathogen of many crop species and partially depends on high temperature and water stress in its invasion of plant tissues. Indeed, in the Davis field plantings, disease symptoms appeared in early- to mid-summer, and were most severe in plants under varying degrees of water stress; well-irrigated plants showed no symptoms. The source of inoculum in these plots is not known, but the severe levels of disease observed in one plot suggest that the pathogen may have become established in the soil on some other crop previously grown at the site. However, M. phaseolina also is known to be seed-borne on many crops, and when diseased plants grown for seed at San Jose, California, were examined, the pathogen was detected in host tissues at least 50 cm above the soil line. Although the limited examination of E. lathyris seed failed to detect the pathogen either on or in seed or in seed debris, this question may warrant further investigation if E. lathyris becomes widely cultivated. Nematode or the genus Meloidogyne are reported.

References

Complete list of references for Duke, Handbook of Energy Crops
Last update Tuesday, January 6, 1998 by aw