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A Wandering Botanist

Tales of a lover of plants, history and travel.

Monday, June 17, 2013

Plant Story: small soapweed, Yucca glauca

Yucca glauca in flower

Standing like candles in the prairie, flowering soapweed yuccas make a handsome display.

A young Yucca glauca.
You could cover all but the
outer tips of the leaves by
setting down a pop can.

Soapweed yucca, Yucca glauca (asparagus family, Asparagaceae) is found from Canada to Mexico across the central U.S., in areas that before settlement were grasslands.

Like other yuccas, Y. glauca has a rosette of leaves and can live many years. The plants start as tiny rosettes of short thin leaves and as the plant gets older, the leaves get more numerous and longer.

The leaves are tough and fibrous, with a sharp point at the tip. Cattle generally avoid eating the leaves. Biologists generally avoid walking where the leaves will stab their legs. The evening volleyball game at Cedar Point Biological Station featured the phrase “stucka by a yucca” for players who ran heedlessly after a stray ball into the plants surrounding the improvised volleyball court.

Fibrous leaves with stiff points on the end can be useful. Plains tribes and early settlers carefully peeled back the tip, keeping a long fiber attached, and had an instant needle and thread. The fiber is pretty tough and makes an effective little thread.

Yucca glauca flowers

Although yucca leaves are strong and well-defended, Yucca glauca flowers are totally edible. Soft, pleasant and appealing, after washing to remove bugs, they can be eaten raw or cooked, boiled or fried. The deer, elk and pronghorn know that and frequently strip all the flowers off a flower stalk.

Bumping a yucca in flower usually results in several small white moths flying away. Yucca glauca is like other yuccas in being pollinated by a moth who lays her eggs on the developing seeds. She is both a pollinator and a seed-eater. The relationship is long-standing so that the flowers and seeds of yuccas are modified to accomodate this moth. If she doesn’t carry pollen between flowers, no seeds are produced because while plant requires pollen from another plant in order to develop seeds, it has no mechanism for getting that pollen unless a yucca moth specifically carries pollen between plants. It has no rewards or attractions for other insects.

The seeds develop in three neat columns. Generally a moth larva eats its way down one column, growing bigger all the time. The female moth may lay eggs on two of the columns of seeds, but never on all three. Obviously, there can be problems if two females target the same flower, but generally they leave scent marks to warn later arrivals to go elsewhere. Since this relationship depends on the plant getting some seeds while feeding the moth, avoidance mechanisms usually work and each yucca flower both feeds one or two moth larvae and develops a column of seeds.

Yucca glauca roots
Compare the drying leaves,
top left, to the size of the roots!

The name soapweed is applied to Yucca glauca because there are saponins, soapy compounds, in the roots. Native Americans and settlers used yucca roots as a source of soap. I have tried it. It doesn’t make much lather but it does remove dirt and grease. Making soap from ashes and lye is a lot more work than gathering yucca roots.

Like most plants of the prairie, soapweed yuccas are deeply rooted. The prairie is a grassland with relatively short plants in part because it is too dry for bigger plants to survive. One mechanism for surviving the periodic droughts of the prairies is having deep or widespread roots that seek water in a large volume of soil. Digging up plants is hard work but sometimes I spotted them at the bottom of eroding banks and road cuts. To the left a big old yucca, showing the massive roots that grow below a modest-sized plant.

A Wandering Botanist Tales of a lover of plants, history and travel. Monday, June 17, 2013 Plant Story: small soapweed, Yucca glauca Yucca glauca in flower Standing like

U.S. Forest Service

United States Department of Agriculture

Plant of the Week

Yucca glauca range map. USDA PLANTS Database.

Close-up view of a soapweed yucca flower. Photo by Charlie McDonald.

Soapweed yucca flower stalks. Photo by Charlie McDonald.

Soapweed yucca plant growing in the foothills of the Sandia Mountains on the Cibola National Forest. Photo by Charlie McDonald.

Soapweed Yucca (Yucca glauca)

By Charlie McDonald

Soapweed yucca is one of about 40 yucca species, all of which are native to the New World. It grows in dry rocky soils throughout the Great Plains and is most abundant in short grass prairies and desert grasslands. These plants have a long history of beneficial use. As the name implies, the crushed roots of soapweed yucca produce a lather that makes a good soap or shampoo. The lathering substances called saponins are found in many plants, but are exceptionally concentrated in yucca roots. The dried leaves of soapweed yucca can be woven into baskets, mats, or sandals. The strong coarse leaf fibers can be extracted to make cordage.

Roots labeled “yucca root” are often sold in grocery stores. These roots are actually cassava or manioc (Manihot esculanta). This woody shrub has a starchy tuberous root that is a staple food in the tropical regions where it grows. The roots of true yuccas are generally too fibrous and too full of toxic saponins to be used as food.

Yuccas and yucca moths are the classic example of a plant and animal obligate symbiotic relationship where each organism requires the other to survive. Yucca moths are the only insects that can successfully pollinate yucca flowers and the developing yucca fruits are the only larval food source for yucca moths.

U.S. Forest Service United States Department of Agriculture Plant of the Week Yucca glauca range map. USDA PLANTS Database. Close-up view of a soapweed yucca flower. Photo by Charlie