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Asclepias syriaca L.

Asclepiadaceae
Common milkweed

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 unpublished.

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

Uses

Gaertner (1979) speaks of milkweed as "the greatest underachiever among plants. Its potential appears great, yet until now it has never been continuously processed for commerical purposes." The latex has been suggested as a suitable replacement for chicle in chewing gum rather than for rubber in tires. It was once cultivated in Europe for bee fodder and fiber. Two types of fiber are obtainable, the long, quite strong but brittle bast fiber and the seed hairs. Pulp from the fiber yields a good paper. During World War II, the seed hairs, being rather springy, light and waterproof, were used to replace kapok in life jackets. Flowers are reported to be a source of sugar and have been used, with sugar and lemon, to make wine. Gaertner says, "Milkweed makes an attractive pot herb in many forms: first as a young shoot, then as unopened buds, and finally as pods, while these are still young, and the seeds are not yet differentiated." I have tried all these, discarding my first "potlikker", and found them quite palatable. Some Indian groups dried the flower buds in summer for use in winter soups (Erichsen-Brown, 1979). I have not tried the "boiled roots" which Kloss (1939) states "taste similar to asparagus." I suspect this is a typo for shoots.

Folk Medicine

According to Hartwell (1967–1971), the leaves and/or latex are used in folk remedies for cancer, tumors, and warts. Reported to be alterative, anodyne, cathartic, cicatrisant, diaphoretic, diuretic, emetic, emmenagogue, expectorant, laxative, and nervine. Milkweed is a folk remedy for asthma, bronchitis, cancer, catarrh, cough, dropsy, dysentery, dyspepsia, fever, gallstones, gonorrhea, moles, pleurisy, pneumonia, rheumatism, ringworm, scrofula, sores, tumors, ulcers, warts, and wounds (Duke and Wain, 1981; Kloss, 1939; Erichsen-Brown, 1979). One reported Mohawk antifertility concoction contained milkweed and jack-in-the-pulpit, both considered contraceptive. Dried and pulverized, a fistful of milkweed and three Arisaema rhizomes were infused in a pint of water for 20 minutes. The infusion was drunk, a cupful an hour, to induce temporary sterility (Erichsen-Brown, 1979). Cherokee used the plant for backache, dropsy, gravel, mastitis, venereal diseases, and warts (Hamel and Chiltoskey, 1975). In homeopathy, the rhizome is used as an antiedemic and emmenagogue, in dropsy and dysmenorrhea (List and Horhammer, 1969 1979).

Chemistry

According to Hager's Handbuch (List and Horhammer, 1969–1979), the latex contains 0.1–1.5% caoutchouc, 16–17% dry matter, and 1.23% ash. Also they report the digitalis-like mixture of a- and b-asclepiadin, the antitumor b-sitosterol, and a- and b-amyrin and its acetate, dextrose and wax. The seed oil contains 4% paimitic-, 1% stearic-, 15% oleic-, 15% 11-octadecanoic-, 53% linoleic-, 1% linolenic; 10% 9-hexadecenic-, and 2% 9,12-hexadecadenic-acids. Condurangin has also been reported from the seed, with at least 9 active cardenolids, among them uzarigenin, desgiucouzarin, syriogenin, syriobioside; also xysmalogenin. The sprouts, eaten like asparagus, e.g. among Yugoslavs, contains asclepiadin, nicotine, b-sitosterol, a- and b-amyrin, and tannin.

Description

Perennial herb with long-spreading rhizomes. Stems stout, erect, to 2 m tall, with short downy hairs and milky juice; leaves opposite, oblong, rounded, 1–2.6 dm long, 0.4–1.8 dm broad, with prominent veins; upper surface smooth, lower covered with short white hairs and strong transverse nerves. Flowers sweet-smelling, pink to white, in large, many-flowered, axillary and apical bell-like clusters; corolla lobes 6–9 mm long, hoods 3–4 mm high; follicle grayish, hairy, with soft spiny projections, 1–3 mm high, slenderly ovoid, 2.5– 3.5 cm thick. Seed brown, flat, oval, 6 mm long, 5 mm wide, with a tuft of silky white hairs apically (Reed, 1970)

Germplasm

Reported from the North American Center of Diversity. Milkweed clones differ substantially in height, earliness of maturity, length and circumference of pods, as well as rubber content (Campbell, 1983). (2n= 22, 24)

Distribution

Fields, pastures, roadsides, thickets, and woods in the eastern U.S., except Gulf States, north on into Canada.

Ecology

Estimated to range from Cool Temperate Dry to Wet through Warm Temperate Dry to Wet Forest Life Zones, milkweed is estimated to tolerate annual precipitation of 4 to 12 dm, annual temperature of 8 to 14°C, and pH of 5.5 to 7.3.

Cultivation

Since milkweed is usually harvested from the wild, there are few data dealing with its cultivation. Campbell (1983) spaced his rows at 0.7 m apart, planting his seed at the rate of 100/1.5 m, 2 cm deep, on an Aquic Hapludult pH 6.2 (2.0% organic matter). Seed dormancy is broken by removal of the seed coat or with gibberellic acid or kinetin, which appear to counteract an inhibitor located in the seed coat. Nondormant seeds can germinate at 14–35°C and apparently emerge best when planted 1–2 cm deep.

Harvesting

Shoots are harvested for forager food in spring, flower buds in midsummer, green pods in late summer. Early fall, just before the pods dehisce, might be the best time to harvest for floss. Those interested in floss may be surprised to learn that only 1–3% of the flowers produce mature pods. According to Gaertner (1979), "It was proven much more efficient to collect from the abundant wild stands rather than to cultivate the plants."

Yields and Economics

Buchanan and Duke (1981) present a table showing an array of products available from unimproved wild milkweed and a proposed developed milkweed.

Table. Possible products and yields from milkweed (Asclepias syriaca) as a potential botanochemical crop.

Unimproved "wild" variety*Developed new crop**
Product Percent of dry plant Yield (kg/ha) Percent of dry plant Yield (kg/ha) Potential uses
Natural rubber 1.6 197 4.0 897 Rubber-goods manufacture
Whole-plant (latex) oil 4.1 505 6.0 1,345 Chemical intermediates
Polyphenol fration 7.2 888 10.0 2,242 Chemical intermediate
Seed—triglyceride oil 1.9 234 0.0 0 Edible oil
Seed—extracted meal 7.2 887 0.0 0 Foods and feeds (51% protein)
Extracted leaf—meal 16.0 1,973 33.0 ,397 Feeds (20% protein)
Floss 11.1 1,368 0.0 0 Insulating material
Bast fiber 11.0 1,356 6.0 1,345 Premium paper-making, cordage
Woody fiber—pod 12.3 1,517 0.0 0 Paper- and board-making, fuel, furfural
Woody fiber—stem shives 27.6 3,404 41.0 9.190
Total 100.0 12,329 100.0 22.416
*Based on dry weight and composi(ion of a typical wild plant assuming a plant density of 107.635/ha.
**Assumes two cuttings per season with the plant not allowed to seed, combined genetic and agronomic improvement.
Source: Buchanan and Duke, 1981

Energy

Annual productivity ranges to ca 13 MT/ha according to the estimates of Buchanan and Duke (1981), assuming a plant density of 107,635 kg/ha.

Biotic Factors

Agriculture Handbook 165 (1960) lists the following as affecting this species: Alternaria sp. (leaf spot), Ascochyta asclepiadis (leaf spot), Cercospora clavata (leaf spot), C. elaeochroma, C. hanseni, C. illinoensis, C. venturioides, Diaporthe arctii (on stems), Didymella cornuta (on stems), Diplodia asclepiadea (on stems), Erysiphe cichoracearum (powdery mildew), Clomerella fusarioides (anthracnose, leaf and stem blight), Phoma asclepiadea (stem blight), Phyllactinia corylea (leaf spot), Phyllosticta cornuti (leaf spot), Phymatotrichum omnivorum (root rot), Puccinis bartholomaei (rust), P. seymouriana, Rhizoctonia solani (root rot), Scolecotrichum asclepiadis (on leaves), Septoria asclepiadicola (leaf spot), ?S. cryptotaeniae, S. incarnata, Sphaeropsis sphaerospora (on stems), Stagonospora zonata (leaf spot), and Uromyces asclepiadis (rust). Nematodes: Meloidogyne incognita, Pratylenchus penetrans (Golden, p.c. 1984). Mosaic virus and Yellows virus are also listed. According to Campbell (1983), there is no evidence of major losses due to insects or disease; however, aphid infestations and viral infections appear common, Aphis nerii B. de F. is sometimes damaging in late summer around Beltsville. As a weed, at densities of 11,000 to 45,200 plants/ha, milkweed reduces corn yields 2–10%, sorghum 4–29%, and soybean 12–19% (Cramer and Burnside, 1982). Glyphosate at 2.2 kg/ha applied at early or late bud stage gave at least 70% control (Cramer and Burnside, 1981).

References

Complete list of references for Duke, Handbook of Energy Crops
Last update December 29, 1997