Walking out in the Tucson Mountains you are likely to come into contact with a mariola plant. If you actually stop to appreciate it (not likely for all but the most botanically-concerned) you might think this plant belongs entirely to the realm of the wild. It’s not the most conventionally attractive plant — after considering the plant for a few seconds you are more likely to move along and marvel at one of the many cacti that occur in the area, or perhaps an attractive wildflower. It would probably come as a surprise to find that this plant may have played an important role during World War II.
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My first encounter with this genus, as a botanist, wasn’t in the field. It was from a conversation with my mentor in the 1990s, and one of the last great botanists, Richard Felger. That conversation happened to also relate to a man who funded the research we were involved in at the time — H.B. Wallace funded much of our research. His father Henry Wallace (vice president under Franklin Roosevelt) had pushed research to search out a domestic source for latex/rubber, and the most promising source for domestic rubber production was guayule and mariola (Parthenium argentatum and P. incanum, respectively).
During World War II, before synthetic rubber was available, we were extremely reliant upon rubber from one plant farmed in one region of the world: Malaysia (but native to the Amazon rainforest), Hevea brasilensis. Don’t forget just how much we use rubber for, especially during wartime; most engines have tubes and gaskets that, without rubber, won’t work. It is a resource that you might take for granted, until that resource becomes scarce.
Our heavy reliance on this single source for rubber was troubling for many reasons: not to mention that it wasn’t just one tree species (many plants produce latex), but a species from an extremely limited gene pool. Even today, most of the trees in the Malaysian rubber plantations are from a limited group of clones and you probably don’t need a degree in agriculture to understand why this is troublesome.
While rubber is native to the Amazon rainforest, plantations of the species are problematic in the region. In nature, rubber trees are rarely found growing next to one another; the diversity of tree species in the Amazon puts a lot of space between individual plants. The presence of South American leaf blight in the region quickly spreads throughout any plantations near where the species is native. Our attempts at creating plantations in the new world have often failed miserably. So even though the new world is where rubber trees are native, they can’t be farmed there without great risk. Also, wild harvesting of rubber is not a dependable, consistent source for rubber — it is incredibly labor intensive and expensive.
During the Allied surrender at Singapore on 16 February 1942, the Japanese began their occupation of Malaysia which was the most important supplier of rubber in the world (at the time). The United States responded by funding a domestic rubber program. This is where our ugly little Parthenium species enter the story.
Parthenium argentatum (also known as guayule) was first considered as an alternate source of rubber in the 1920s, when the plant saw a brief and intense amount of agricultural research after leaf blight decimated the Brazilian rubber industry — the Intercontinental Rubber Company in California (formed by the Rockefeller family) produced 1400 tons of rubber to show that it was possible. Instead of tapping a tree (like you do rubber trees), entire guayule plants are harvested, and macerated; latex is separated from the pulp of the plant with the use of a centrifuge.
This company folded during the pressures of the great depression and the aggressive market hold Malaysian rubber cultivated. But when the Malaysian source was lost to the Japanese, the US interest in domestic rubber production was revived (and this was pushed by the aforementioned vice president Wallace).
Besides guayule, number of other plants, including the related Parthenium incanum (mariola) were grown in experimental fields in the United States. But just days after the US bombed Hiroshima and Nagasaki, Japan, in 1945, Emperor Hirohito gave a recorded radio address to the Empire announcing acceptance to the terms for ending the war that the Allies had set down in the Potsdam Declaration which, among much else, required the end of Japanese occupation of Malaysia.
One would think we’d keep our interest in producing domestic rubber, especially from an arid land plant. But never underestimate the selfishness of monied, special interests: there were a few people in the US who made good money from that trade, and they demanded funding for this research be shut down right away. For a long time the idea of domestic rubber went dormant.
In the 1970s botanists like Richard Felger began taking seriously the idea of looking at arid land plants as potential commercial crops. Global warming wasn’t at the forefront of our minds in those days, but statistically most people in the world live in arid or semi-arid climates. The reason we rely on the kinds of crops we do relates to the history of the invaders and conquerors who travelled the world and began claiming it for themselves. They brought their crops with them, their familiar foods. Richard Felger began considering alternative crops for food, and other resources. It just makes more sense to consider using crops that take less water in a dry world.
Some people listened. And people began to question why we rely on one very vulnerable crop on the other side of the planet for natural rubber.
Fast-forward to October 2015, the Bridgestone Corporation announced the creation of the first tires made entirely of guayule rubber, just after building an experimental farm and biorubber research center in Mesa, Arizona the previous year. Today guayule is grown in Mesa, Eloy, and other areas in Arizona. There are still many applications for which natural rubber is not replaceable, like rubber car tires. Guayule products have many modern applications and benefits over synthetic rubber — those allergic to tropical latex, for example, can use guayule without suffering symptoms.
Guayule-based products are biodegradable, high-performing substitutes to synthetic, petroleum-based products which are hazardous to the environment, and expensive to dispose. The process of making guayule products also uses water-based processes that require no toxic chemicals and are non-polluting.
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If you want to grow a little piece of history (or the future) in your own backyard, you can obtain plants of Parthenium incanum (mariola) at Tohono Chul Park, and at Desert Survivors. This species is the most prevalent in the wild in our region.
You will have to work a little harder to find plants of Parthenium argentatum (guayule) for sale, and may have to comb the various plant sales where they offer the more obscure plants. Or if you happen to be in New Mexico, hit up some of the native plant nurseries there, since, in the US, the species is mostly distributed throughout Texas and New Mexico.
Both species are easy to grow, in full sun and using moderate water. They tolerate temperatures into the mid to low teens fahrenheit and can tolerate some serious drought.