Cabeza de Negro and Barbasco: The Mexican Wild Yams Behind the Hormone Industry

Every story of a medicine made from a plant has a moment when someone finds the plant. For aspirin it was the willow, for quinine the cinchona tree, for digoxin the foxglove. For the steroid hormones of the twentieth century — progesterone, and through it cortisone and the first birth-control pills — the plant was a wild yam growing in the hills of eastern Mexico. The American chemist Russell Marker (1902–1995) had already worked out, in his laboratory at Pennsylvania State College, how to turn a plant compound called diosgenin into progesterone. What he still lacked was a plant that held enough diosgenin, in roots big enough, to make the chemistry worth doing on an industrial scale.

This page tells the story of that plant hunt and of the yams it found: the survey of more than four hundred species, the picture in a botany book in Texas, the 1942 bus journey to Orizaba as Marker himself later described it, the giant root known locally as cabeza de negro, and the ten tons of dried root that became about three kilograms of progesterone. It then follows the higher-yielding yam called barbasco and the Mexican peasants who gathered it for decades, explains how a yam actually builds diosgenin inside its cells, looks at the other plants that make it (fenugreek among them), and closes with what a controlled trial found when wild yam cream was tested for an effect on progesterone in the body. The chemistry of the conversion itself is told on the wing’s page on the Marker degradation, and what came after on the page on cortisone, the pill and the Mexican steroid industry.

Table of Contents

  1. True Yams: The Genus Dioscorea
  2. Four Hundred Plants and a Picture in a Botany Book
  3. The Road to Orizaba, 1942
  4. Cabeza de Negro: A Giant Root
  5. Ten Tons of Root and Three Kilograms of Progesterone
  6. Barbasco and the Yam-Gatherers of Mexico
  7. How a Yam Makes Diosgenin
  8. Diosgenin Beyond the Yam: Fenugreek and Others
  9. Wild Yam Creams and the Progesterone Question
  10. Key Research Papers
  11. Connections

1. True Yams: The Genus Dioscorea

The word “yam” causes a good deal of confusion, especially in the United States, where orange-fleshed sweet potatoes are often sold under that name. The plants in this story are something else entirely. True yams belong to the genus Dioscorea, in their own plant family, the Dioscoreaceae. They are monocots — the great branch of flowering plants that also includes grasses, lilies and orchids — whereas the sweet potato (Ipomoea batatas) is a dicot in the morning-glory family. The two are not close relatives, a point the site’s page on the history of the sweet potato sets out in detail.

Most Dioscorea species are climbing vines that grow from a swollen underground storage organ, the part usually called the root or tuber. Some are staple foods, grown widely in West Africa and Asia. Many wild species contain saponins: soap-like compounds that foam when shaken in water. A saponin is built from two parts — a chain of sugars attached to a non-sugar core. In many yams that core, called the aglycone or sapogenin, is a steroid. The most important of these steroid sapogenins is diosgenin, whose name comes from Dioscorea itself.

Why a Steroid in a Plant Mattered

Diosgenin has the same four-ring carbon skeleton as cholesterol and as the human sex hormones. What makes it different is the side chain at one end of the molecule: in diosgenin it is folded into two extra rings, a structure chemists call a spiroketal. The heart of Marker’s chemistry, worked out between 1938 and 1940, was a way of opening that folded side chain and trimming it back to the short two-carbon side chain of progesterone. Once that was possible, any plant rich in diosgenin became a potential hormone mine. Diosgenin had first been isolated and named by Japanese chemists, Takeo Tsukamoto, Yosio Ueno and their colleagues, from the Japanese yam Dioscorea tokoro, in work published from 1936. Tsukamoto later joined Marker as a co-author on a 1940 paper on diosgenin’s chemistry.

A modern review of the plant steroidal sapogenins describes diosgenin as an industrial starting material for a long list of medicines, including progesterone, testosterone, dexamethasone, DHEA and norethindrone. That list is the long shadow of the yam hunt described below.

Back to Table of Contents

2. Four Hundred Plants and a Picture in a Botany Book

A chemical process is only as useful as its raw material. Marker’s first plant compound, sarsasapogenin, came from sarsaparilla root (Smilax). Beth root (Trillium), a plant of the lily family from North Carolina, contained diosgenin in the form of a glycoside called trillin, and in 1940 Marker and his co-worker J. Krueger turned trillin into progesterone. But according to the American Chemical Society’s landmark history and Marker’s own 1987 oral history, beth root’s roots were too small to be collected in the quantities an industry would need.

So Marker, his students and a number of botanists began to look systematically. According to the ACS booklet, they examined more than four hundred species of plants, mainly in the south-western United States, and described about a dozen new sapogenins along the way. The chemist and historian Jeffrey Seeman, in a 2023 biographical essay, summarises the effort as the collecting of specimens from plants in the south-western United States and Mexico, “discovering many sources of steroidal sapogenins”. In 1940 Marker and his co-workers reported diosgenin in certain American plants, and the large 1947 summary paper on steroidal sapogenins gathered the results of the whole survey.

November 1941

The turning point, as Marker told it, came not in a field but in a book. In November 1941, while in Texas, he looked through an old botany text belonging to a retired botanist. In it was a picture of a large Dioscorea growing along a stream between the towns of Orizaba and Córdoba, in the Mexican state of Veracruz. The text described a root of enormous size: according to the ACS booklet it was said to reach about 100 kilograms, and Marker in 1987 remembered it as weighing “several hundred pounds”. The Science History Institute’s profile gives a more modest figure, roots that “can weigh up to a hundred pounds each”. Whatever the exact number, a root that large, if it contained diosgenin, would solve the problem that beth root could not.

Back to Table of Contents

3. The Road to Orizaba, 1942

Almost everything known about the next few weeks comes from Marker’s own later accounts, chiefly his interview with the historian Jeffrey L. Sturchio in April 1987, together with the ACS landmark booklet and a 1987 student-newspaper interview. It is a good story, and it is told here as Marker told it.

Late in 1941, according to that account, Marker went to Mexico City and was told at the United States Embassy that he would need collecting permits and a botanist to work with. In January 1942 a trip with an assigned botanist set out and was abandoned. Marker then went on alone, travelling by bus to Orizaba and along the Córdoba road. He found a small country store owned by a man named Alberto Moreno, and two of the roots were loaded onto the bus for the return journey. In Marker’s telling the roots were taken from him on the way, and he recovered one of them — about 50 pounds, according to the ACS booklet — by paying a local policeman. That detail, like the others in this episode, rests on his own recollection.

Back in Pennsylvania and Detroit

Back at Penn State, Marker extracted diosgenin from half of the root. The rest he took to Detroit, to the laboratories of Parke-Davis, the company that had funded his research since 1934, and repeated the process there. The sources agree on the outcome: the company’s president declined to produce hormones in Mexico, and the other companies Marker approached also declined. If the Mexican yam was going to be used, Marker would have to do it himself.

Moreno, the storekeeper on the Córdoba road, became the first link in a supply chain that would later carry tens of thousands of tons of root a year out of the Mexican forests.

Back to Table of Contents

4. Cabeza de Negro: A Giant Root

The yam Marker carried home was known locally as cabeza de negro. The phrase is Spanish for “Black man’s head”, and Marker explained in 1987 that it came from the look of the tuber’s crown: a dark, rough, curly-looking mass that sits partly above the ground. It is a period name, and it is given here only because it is the name under which the plant entered the history of chemistry.

Which Species?

The sources do not agree on the plant’s botanical name. Marker himself, in the oral history, called it Dioscorea macrostachya. Other accounts identify cabeza de negro as Dioscorea mexicana. The safest statement is the one the sources support: cabeza de negro was a large Mexican wild yam of the genus Dioscorea, identified in different sources as D. macrostachya or D. mexicana.

What Made It Valuable

Its value lay in two things together: the root contained diosgenin, and the root was very large, so that a single plant gave a quantity of raw material that would have needed hundreds of small beth-root rhizomes. The diosgenin sits in the root as saponins, bound to sugars. Freeing it means splitting off the sugars (the step chemists call hydrolysis) and extracting the steroid core, which is then the starting point for Marker’s laboratory degradation to progesterone.

Wild yams like this were not crops. They grew scattered through forest and scrub, and every root used in the early years had to be found and dug up by hand. That fact would shape the social history of the industry that followed.

Back to Table of Contents

5. Ten Tons of Root and Three Kilograms of Progesterone

With no company willing to back him, Marker financed the next step himself. In the autumn of 1942, according to the Science History Institute, he put about half of his savings into it. He arranged with Alberto Moreno to have local people collect cabeza de negro and dry it in the sun. The amount, by the ACS account, was about ten tons of root.

The dried root was taken to Mexico City, where a small extraction works soaked it in alcohol and concentrated the extract into a thick syrup. Marker carried the syrup to New York. There, in the laboratory of Norman Applezweig, he converted it into progesterone, in return for which Applezweig’s firm kept one third of the product.

How Much Progesterone?

The ACS booklet, the Science History Institute and the 1987 Daily Collegian interview all give the result as about three kilograms of progesterone. The ACS booklet calls it “then the largest lot of progesterone ever produced” and gives its value at $80 a gram. Marker himself, in the oral history, said he kept “a little over two kilos” after Applezweig’s third, which fits a total of about three. By comparison, his largest earlier lot, made at Penn State from pregnanediol isolated from urine supplied by Parke-Davis, had been about 35 grams.

The arithmetic is striking. Ten tons is ten thousand kilograms; three kilograms of product is roughly 0.03 percent of the dried root’s weight. Even so, the yield was enough to show that a wild plant gathered by hand in rural Mexico could supply hormone in amounts that had never existed before. That demonstration led directly to Marker’s move to Mexico City and to the founding of a company there in early 1944, a story told on the Life and Career page.

Back to Table of Contents

6. Barbasco and the Yam-Gatherers of Mexico

Cabeza de negro was the yam that started the industry, but it was not the yam that sustained it. Marker knew of a second species, called barbasco, which he identified as Dioscorea composita — a name consistent with the modern literature, where D. composita is studied as a diosgenin source in Mexico (an analytical method for measuring diosgenin in it was published in 1972). According to the ACS booklet, barbasco held about five times as much diosgenin as cabeza de negro. Marker described its root in 1987 as containing almost pure diosgenin and said it grew near Tierra Blanca, in Veracruz. In wartime it was hard to ship from there, so he began with cabeza de negro and switched to barbasco in 1945, at Botanica-mex, the company he founded after leaving his first Mexican venture.

Root Carried Out by Hand

As the Mexican hormone industry grew in the 1950s and 1960s, the demand for barbasco grew with it. Marker said in 1987 that in the 1970s about 75,000 to 80,000 tons of root a year had been carried out of the forest by hand, that from about 1974 the Mexican government took over root collection, and that barbasco takes at least four years to grow in cultivation. Those are his figures, given from memory.

The Historian’s View

The historian Gabriela Soto Laveaga has studied this side of the story — the people who dug the roots rather than the chemists who processed them. In a 2005 paper she traces how the worldwide search for cheap steroids made barbasco the raw material of choice, and how gathering wild yams changed rural Mexico. Barbasco, she writes, gave an “erstwhile ‘weed’” monetary value; the trade gave rise to peasant organisations and to government efforts to control barbasco production. Her later book, Jungle Laboratories: Mexican Peasants, National Projects, and the Making of the Pill (2009), develops the theme at length.

The point of her work is a simple one that the laboratory histories tend to miss: the pill and cortisone rested not only on a chemical reaction but on the labour of thousands of rural gatherers who found, dug and carried the yams.

Back to Table of Contents

7. How a Yam Makes Diosgenin

For most of the twentieth century, how plants actually made diosgenin was not known in detail. The broad outline was clear — it is a steroid, and plants make steroids, like animals do, from smaller building blocks — but the enzymes that fold the side chain into its distinctive spiroketal had not been identified.

Cholesterol First

A 2019 study in Nature Communications by Christ, Weng and colleagues filled that gap. They showed that plants make diosgenin from cholesterol, the same molecule found in animal cells, and that the key steps are carried out by pairs of cytochrome P450 enzymes, a large family of enzymes that add oxygen atoms to molecules. These enzyme pairs oxidise the cholesterol side chain at specific positions and so form the spiroketal rings. The authors describe diosgenin as “the single most important precursor for the world steroid hormone industry”.

The Same Trick, Twice

Their most surprising finding was evolutionary. The ability to make diosgenin turned out to have arisen independently at least twice: once in a monocot, Paris polyphylla (a woodland herb of Asia), and once in a eudicot, fenugreek. The two lineages arrived at the same molecule using different P450 enzymes — an example of what biologists call convergent evolution. The yams, which are monocots like Paris, belong to the same broad branch of plants as the first of those two lineages.

Barbasco’s Genes

For barbasco itself, a 2015 study by Wang and colleagues sequenced the genes active in Dioscorea composita (a transcriptome) and found genes for most of the steps of the steroidal sapogenin pathway. The building blocks came mainly from the mevalonate pathway, the same route animal cells use to make cholesterol, and the genes were most active in the tuber and the leaves — consistent with the tuber being the plant’s store of diosgenin.

Work like this matters for the yam’s future as well as its past: once the genes are known, diosgenin can in principle be produced in other organisms without digging up wild plants at all.

Back to Table of Contents

8. Diosgenin Beyond the Yam: Fenugreek and Others

Although the Mexican yams made diosgenin famous, they are far from its only source. The plants that make it span several unrelated families:

From Yam to Industry, and Beyond

The 2024 review by Pathak and Negi surveys the chemistry built on diosgenin: its use as the starting material for progesterone, testosterone, dexamethasone, DHEA, norethindrone and other steroid drugs, and the large body of laboratory and animal research on diosgenin’s own biological effects. Most of that pharmacological research is preclinical — done in cells and animals — rather than in people.

Diosgenin is no longer the only industrial raw material. As the page on the steroid industry after Marker explains, plant sterols from soybeans and other crops, converted partly by microbes, later took over much of the work the yams once did.

Back to Table of Contents

9. Wild Yam Creams and the Progesterone Question

The fact that progesterone was once made from wild yams led, decades later, to a common belief: that wild yam itself, eaten or rubbed on the skin as a cream, supplies progesterone or acts like it. Creams made from the North American wild yam, Dioscorea villosa, have been sold on that idea. The history on this page shows where the belief comes from — and also where it parts company with the history.

What Marker’s Chemistry Actually Did

Diosgenin is not progesterone. It became progesterone in Marker’s process only through a series of deliberate laboratory steps: heating with acetic anhydride at about 200 °C to open the side chain, an oxidation step, and hydrolysis. The conversion was a laboratory process, carried out by chemists, in glassware.

The 2001 Trial

In 2001 Komesaroff and colleagues tested a wild yam cream directly. In a double-blind, placebo-controlled crossover trial, 23 healthy menopausal women used the wild yam cream and a placebo cream in turn. The researchers measured symptoms, blood lipids, and a panel of hormones in blood and saliva. They found no change in any of the hormone levels, including serum and salivary progesterone, and no statistically significant difference from placebo in symptoms. No side effects were reported.

An Animal Finding

A 2008 study by Wojcikowski and colleagues looked at Dioscorea villosa extract from a different angle. Rats fed the extract for 28 days showed no signs of acute toxicity, but they did show increased markers of kidney fibrosis (scarring) and signs of inflammation in the liver. The finding comes from animals at the doses used in that study, and how it relates to human use has not been established; it is reported here as a laboratory finding.

Taken together, the research describes a sharp line between the yam as a raw material for laboratory hormone synthesis, which it was, and the yam as a source of progesterone in the body, which the one controlled trial of a wild yam cream did not find. The site’s page on micronized progesterone and synthetic progestins describes what the research says about the prescribed forms.

Back to Table of Contents

Key Research Papers

  1. Seeman JI. Russell Earl Marker and the Beginning of the Steroidal Pharmaceutical Industry. Chem Rec. 2023;23(4):e202300048. PubMed PMID: 36995067
  2. Lehmann PA, Bolivar A, Quintero R. Russell E. Marker. Pioneer of the Mexican steroid industry. J Chem Educ. 1973;50(3):195-9. PubMed PMID: 4569922
  3. Laveaga GS. Uncommon trajectories: steroid hormones, Mexican peasants, and the search for a wild yam. Stud Hist Philos Biol Biomed Sci. 2005;36(4):743-60. PubMed PMID: 16337559
  4. Tsukamoto T, Ueno Y. Untersuchung der Glykoside von Dioscorea Tokoro Makino (I. Mitteilung). Yakugaku Zasshi. 1936;56(10):802-807. DOI: 10.1248/yakushi1881.56.10_802
  5. Marker RE, Tsukamoto T, Turner DL. Sterols. C. Diosgenin. J Am Chem Soc. 1940;62(9):2525-2532. DOI: 10.1021/ja01866a072
  6. Marker RE, Turner DL, Ulshafer PR. Sterols. CIV. Diosgenin from Certain American Plants. J Am Chem Soc. 1940;62(9):2542-2543. DOI: 10.1021/ja01866a076
  7. Marker RE, Krueger J. Sterols. CXII. Sapogenins. XLI. The Preparation of Trillin and its Conversion to Progesterone. J Am Chem Soc. 1940;62(12):3349-3350. DOI: 10.1021/ja01869a023
  8. Marker RE, Wagner RB, et al. Steroidal sapogenins. J Am Chem Soc. 1947;69(9):2167-2230. PubMed PMID: 20262743
  9. Sánchez GL, Medina Acevedo JC, Soto RR. Spectrophotometric determination of diosgenin in Dioscorea composita following thin-layer chromatography. Analyst. 1972;97(161):973-6. PubMed PMID: 4651956
  10. Christ B, Xu C, Xu M, Li FS, Wada N, Mitchell AJ, Han XL, Wen ML, Fujita M, Weng JK. Repeated evolution of cytochrome P450-mediated spiroketal steroid biosynthesis in plants. Nat Commun. 2019;10(1):3206. PubMed PMID: 31324795
  11. Wang X, Chen D, Wang Y, Xie J. De novo transcriptome assembly and the putative biosynthetic pathway of steroidal sapogenins of Dioscorea composita. PLoS One. 2015;10(4):e0124560. PubMed PMID: 25860891
  12. Pathak N, Negi AS. Plant based steroidal and triterpenoid sapogenins: Chemistry on diosgenin and biological aspects. Eur J Med Chem. 2024;279:116915. PubMed PMID: 39366126
  13. Komesaroff PA, Black CV, Cable V, Sudhir K. Effects of wild yam extract on menopausal symptoms, lipids and sex hormones in healthy menopausal women. Climacteric. 2001;4(2):144-50. PubMed PMID: 11428178
  14. Wojcikowski K, Wohlmuth H, Johnson DW, Gobe G. Dioscorea villosa (wild yam) induces chronic kidney injury via pro-fibrotic pathways. Food Chem Toxicol. 2008;46(9):3122-31. PubMed PMID: 18662738

PubMed Topic Searches

  1. PubMed: Dioscorea diosgenin
  2. PubMed: barbasco Mexico
  3. PubMed: diosgenin biosynthesis
  4. PubMed: diosgenin progesterone history
  5. PubMed: wild yam Dioscorea villosa

Further Reading

Back to Table of Contents

Connections