The Genus Parthenium
Guayule, Mariola
Family: Asteraceae
Parthenthenium is a genus of about 12 species native to the southwestern United States, and Mexico. Even though the plants are often somewhat inconspicuous, they include some ecologically interesting plants, and some important economic plants with an interesting history.
Maybe most famous of the economic uses of this genus dates back to World War II: before there was synthetic rubber, all rubber came from one clone of a single species (Hevea brasiliensis), mostly grown in SE Asia. At one point the Japanese took over the plantations, and the only other source of rubber was from wild-tapped plants in tropical Americas which was an inconsistent source. Rubber is important as a seal, insulation, and in many many more applications that eventually was replaced by synthetics. But during this time, there was no alternative.
However, the reliance on one clone from one species in one part of the world was short-sighted and Vice president Henry Wallace (under Franklin Roosevelt) was an agriculture man who started a domestic rubber program to expand the sources of latex/rubber. In Tucson experimental farms growing a few species of Parthenium were started (Parthenium species yield latex when macerated and filtered). Two species in particular, Parthenium argentatum, and P. incanum, were farmed for their latex.
After the United States bombed Japan, they got control of the rubber plantations and special interests groups concerned with maintaining a monopoly on latex had the domestic rubber program shut down.
Before the WWII rubber emergency, in the 1920s, the plant saw a brief and intense amount of agricultural research when the Intercontinental Rubber Company in California produced 1400 tons of rubber after South American Leaf Blight decimated the Brazilian rubber industry.
Today, there are a few companies growing Parthenium in a renewed interest in non-synthetic latex.
The Ragweed Borer Moth (Epiblema strenuana) causes galls on the stems of Parthenium species and uses the plant as a larval host.
The name Parthenium is an evolution of the Ancient Greek name parthenion, which referred to feverfew (Tanacetum parthenium) of which many parallels/similarities are noted to Parthenium species, some of which are sometimes called feverfew.
Guayule
Parthenium argentatum
Rounded evergreen shrub reaches about 3’ tall and about 4’ wide. White to cream flowers are born on the tops of the plant in warm weather.
Full sun, moderate water with good drainage, hardy to 15°F.
The species name is a Latin word, argentum, which means "silver".
Naturally occurring in Texas, south into Mexico on calcareous soils, 3200-5000 ft. Hybrids between Parthenium argentatum and P. incanum have been noted.
Photo by mirrin86, iNaturalist
Parthenium argentatum on SEINET
Mariola
Parthenium incanum
Rounded evergreen shrub reaches about 3’ tall and about 4’ wide. White to cream flowers are born on the tops of the plant in warm weather.
Full sun, moderate water with good drainage, hardy to 15°F.
The species name, incanum, means grayish or hoary.
Found on gravelly slopes and plains from 2,500-5,000 ft. in southern Nevada, southern Utah, Arizona, New Mexico and southwestern Texas; south into southern Mexico. Hybrids between Parthenium argentatum and P. incanum have been noted.
Photo by Chuck Sexton, iNaturalist
Parthenium incanum on SEINET
Tree Guayule
Parthenium tomentosum
This is a plant that in habitat can get to 18’ tall, though most often seen at about 6-10’. It is an evergreen shrubby tree that flowers in the warm season with cream-off-white flowers.
Plant in part to full sun with good drainage and moderate water. Plants are frost tender and should be protected from hard cold snaps.
This species is native throughout Mexico.