One of the most distinctive plant families of the desert are the yuccas. They grow throughout the American Southwest, Mexico, and South America. Yuccas were always considered valuable by native tribes who used them for food, fiber, and soap-making. People still gather the edible fruits, eat the flower petals in soups and salads, peel apart the leaves for the long, tough fibers, and boil the roots to make soap. Though uncommon now, you can still buy all of these products in specialty market places.
Though there are 40 – 50 species, only a few are common in the Big Bend region.
One of the most visible yuccas in this region is the Spanish Dagger. At 8 feet or more in height, it is an impressive plant. The leaves are long, thick, and very sharp so be careful when approaching them.
Their huge flower heads are quite noticeable in the spring when large numbers of them frequently bloom at the same time. Each flower starts out with a dark wine-colored tip, but it fades to a rich cream color as it opens.
Thompson Yucca (Yucca rostrata)
This is the beauty queen of the yucca tribe. It grows to great heights (20–30 feet), mature ones may have multiple shaggy trunks, and many trunks divide into several branches. The rosettes of leaves at the top, and the tall white flower stalks make a showy spectacle year round.
Thompson Yucca is the most popular yucca for gardeners. Tens of thousands of them have been dug up for resale in nurseries throughout the southwest. The plants are easy to propagate and grow, and they live a long time.
You can distinguish Thompson Yuccas from Spanish Daggers by their leaves. Spanish Dagger leaves are thick and stout, but Thompson Yucca leaves are thin and narrow. Also, they have have horny or saw-toothed edges. A little hook, or “beak” grows on the tip of the fruits, a feature which gives this yucca one of its other popular names, the “Beaked Yucca.”
Native residents of the Southwest quickly discovered that the juices of the Soaptree Yucca makes an excellent soap. They bathed in it, washed their hair in it, and used it for laundry. It is particularly good for woolens because it does not make the fibers clump like modern soaps and shampoos do. Though the Soaptree Yucca can grow as tall as 30 feet, most are not much taller than a grown adult.
The Soaptree Yucca likes higher elevations, so you will probably see more of them in the Big Bend Ranch State Park than you will in the national park. The leaves are long, thin, and have a silvery edge. Also, you will usually find a nest of curly fibers growing near the base of the leaves. The flower heads are not as spectacular as many other yuccas, but the plant has a fine, feathery look to it that gives it a unique beauty.
Yuccas and Moths
Yuccas are pollinated exclusively by yucca moths with whom they have developed a uniquely close relationship. For each kind of yucca, there is one particular yucca moth that pollinates it. Without the moth, the yucca cannot set seed; the moth relies entirely on the yucca for food and shelter. During the day, moths hide inside yucca blossoms, safe from predators. At night, they come out, pollinate the flowers, and lay their eggs.
Unlike most moths, yucca moths do not have the long nectar-sipping tongue of their relatives. Instead, the female yucca moth has a set of tiny tentacles around her mouth. She uses the tentacles to gather yucca pollen which she then rolls into a tiny ball which just fits a depression under her “chin.”
Once she’s collected enough pollen, she flies to another blossom and checks to make sure that no other moth has been there before. She will not lay eggs on a blossom that has another moth’s eggs in it. When she finds a suitable blossom she punches a hole in the base of the flower near the ovaries and deposits a few eggs. Then she climbs the flower pistil, removes the ball of pollen from under her chin and carefully packs it into a receptacle in the stigma, thereby ensuring that the flower is pollinated and will produce lots of juicy seeds for the moth’s larva.
Moths are careful not to lay too many eggs in one flower. If the moth gets greedy and lays too many eggs in one place the plant drops the pod, thereby losing the seeds but also killing the over-greedy larvae.
When the eggs hatch the larvae feed on the growing seeds. The seeds match the larva’s nutritional needs perfectly, so each larva needs only a few seeds to mature. When the larva is fully developed it chews a little hole in the yucca pod wall, climbs out, and drops to the ground. Then it burrows several inches underground where it goes into the cocoon stage to wait out the winter. When warm temperatures and summer rains arrive, the yuccas begin to bloom again and the pupated yucca moths emerge from underground to start the cycle anew.