D e s e r t E x p o s u r e
December 2011
Southwest WildlifeThe Giving Tree
From food to tools to medicine, the yucca is a veritable Walmart for desert dwellers.
by Jay Sharp
If — like some of our neighbors — you have in your yard a broad-leaf yucca with the last spring and summer flower stalk still standing, you might consider decorating it for the coming holiday season. For instance, you can hang ornaments from the tips of leaves. You can place a cluster of lights (taking care not to create a fire hazard) and ornaments at the tip of the stalk, where the plant's cluster of flowers bloomed during the summer. You can create a distinctively Southwest "Christmas tree."
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The torrey yucca, a signature plant of our Chihuahuan Desert, with a cactus wren perched in its bloom cluster. (Photos by Jay W. Sharp) |
While most cacti bristle with arrays of modified leaves, or spines, that look like pins and needles or fishhooks, most yuccas — unlikely members of the symbolically peaceful lily family — guard themselves with armaments of leaves, not spines, that resemble sabers. Like the cacti, the evergreen yuccas serve up tasty meals to various animals in spite of their threatening botanical weaponry.
In fact, the yuccas held such an important role in the diets (as well as the economies) of Native Americans that the plants became embedded in folk histories, ceremony and tradition. For one example, in The Dîné: Origin Myths of the Navaho Indians (recorded by Aileen O'Bryan of the Bureau of American Ethnology of the Smithsonian Institution in 1956), "The Plan, or Order of Things," declared that "There was a plan from the stars down…
"…they planned how a husband and a wife should feel toward each other, and how jealousy should affect both sexes. They got the yucca and the yucca fruit, and water from the sacred springs, and dew from all the plants, corn, trees and flowers. These they gathered, and they called them tqo alchin, sacred waters. They rubbed the yucca and the sacred waters over the woman's heart and over the man's heart. This was done so they would love each other; but at the same time there arose jealousy between the man and the woman, his wife."
Emblems of the Desert
The yuccas, emblematic of the desert, typically suggest sprays of broadswords or rapiers that crown either a root-stem, a single stem or branching stems. Altogether, at least four dozen species occur in the yuccas' native range of the western United States, Mexico, Central America and the West Indies. More than a dozen species populate our Southwestern region, growing from the bottoms of desert basins to the upper slopes of mountain ranges.
One of the most widely distributed, the banana yucca, has extended its range "from the mountains of the eastern Mohave Desert of California across southern Nevada, southwestern Utah and southwestern Colorado as far east as Trinidad. From this northern boundary it extends south and southeast across northern and central Arizona and the greater part of New Mexico into southwestern Texas," according to Willis H. Bell and Edward F. Castetter, writing in Ethnobiological Studies in the American Southwest.
Collectively, the desert species of yucca, all well equipped for surviving under harsh conditions, have several distinctive characteristics.
Their sharply pointed succulent (water-storing) leaves bear greenish, grayish- or bluish-green waxy skins that both reflect the heat of the desert sun and restrict the loss of stored water. The rosette leaf arrangements and the often-channeled upper leaf surfaces function as conduits for funneling water from rains, snowmelt and dew into the plant stem and root system. Most desert species' leaves signal their botanical identity with tendrils of fiber that curl away from the edges.
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The torrey yucca, leaves and blooms, overlooking the Organ Mountains, east of Las Cruces. Note that the leaves have tendrils of fiber curling away from the edges. |
The yucca stems have a "vascular" structure — scattered bundles of specialized tissues that store and conduct water. Some species — for instance, Our Lord's Candle, a yucca of the western Sonoran Desert — have very abbreviated stems, or "root stems," that barely reach the surface of the ground. Others, like the banana, or datil, yucca (of all three United States' deserts) have very short or sometimes "reclining" stems. The soaptree yucca (Chihuahuan and Sonoran Deserts) and the torrey yucca (Chihuahuan Desert) have stems, sometimes shaggy with skirts of dead leaves, that can range from several inches to 10 to 15 feet in height. That star of the yuccas, the Joshua tree (Mojave and Sonoran Deserts), has multiple branching fibrous stems as tall as 40 or 50 feet. Some yucca species that grow in dune fields — for instance, the soaptree yucca of northern Chihuahua's Médanos de Samalayuca (Sand Dunes of Samalayuca) — have stems that grow taller very rapidly, as much as several inches per year, to keep the leaf rosettes from being engulfed by the marching dunes.
Some species have both shallow radial root systems and deep tap roots. The radial roots intercept rainwater and snow melt as it soaks into the upper soil layers. (Other species have a more limited root system.) The tap roots reach for the deeper water in the lower soil layers, and they have fleshy tissues for storing and conducting water. The roots stake out a claim for water and nutrient resources, guarding a plant's "territory" against encroachment by neighboring yuccas and other plants.
Typically, the yuccas produce a dense bouquet of creamy white flowers, sometimes with a reddish or purplish tinge, on a single stalk in the spring and early summer. The flowers attract a specialized pollinating moth species. The yuccas follow with an equally dense cluster of fleshy green edible fruits during the summer, attracting a veritable lunch line of consumers.
Like cacti, the yuccas minimize the evaporation of water from their tissues by opening their stomata (leaf pores) during the coolness of night (rather than during the heat of the day) to take in the carbon dioxide required for photosynthesis. They open their stomata as darkness falls and effectively inhale carbon dioxide through the night. They put it in short term storage by combining it, biochemically, with an organic acid. They close their stomata as darkness gives way to sunlight, then free their store of carbon dioxide internally. Fueled by solar energy, they begin the process of photosynthesis, which they continue through the day.
By contrast, many other plants open their stomata for business at sunrise. They take in carbon dioxide during the heat of the day and proceed directly with photosynthesis, without the intermediate step of short-term chemical storage. More efficient, these plants tend to grow more rapidly, but they also squander much of their water store by evaporation through their stomata.
Family Members
Generally, the yuccas of the Southwest fall into one of two groups: the broad-leaf yuccas, with mature leaves that measure roughly two inches in width, and the narrow-leaf yuccas, with mature leaves that measure well under one inch in width. Some of the better known species include the broad-leaf torrey and banana yuccas and the narrow-leaf soaptree yuccas, Our-Lord's-Candle and, of course, the Joshua tree yucca.
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The soaptree yucca in bloom. |
The torrey yucca, or Spanish bayonet, a signature plant of our Chihuahuan Desert, closely resembles the banana yucca, with both having similar leaves and radiating root systems. In fact, the two species may be hybridizing, according to Clark Champie in his Cacti and Succulents of El Paso. The torrey yucca, however, has a rising and shaggy skirted stem that may reach 15 feet or more in height. It produces creamy white, purple-tinged flower clusters and fleshy fruits on a stalk that sometimes extends for several feet above the leaf rosette.
The banana yucca holds residence in the Chihuahuan, Sonoran and Mojave Deserts. Its 30-inch-long leaves typically occur in an open cluster atop abbreviated stems. It has a fibrous and highly branched radiating root system. Its flower stalk reaches as much as 40 inches in height, bearing fleshy white flowers with a red or purple tinge. Its produces a green, fleshy, banana-shaped fruit, hence its common name.
The soaptree yucca, among the most common of the Chihuahuan and Sonoran Desert yuccas — and New Mexico's state flower — has pale green leaves with whitish margins. As it grows and matures, it often develops a branching, shaggy stem perhaps 15 feet in height. It has both a radiating root system and a tap root. Each stem branch produces a cluster of cream-colored. bell-shaped flowers and brown woody seed capsules that tip a flower stalk several feet in length.
Our-Lord's-Candle, native to the western Sonoran Desert, has a decorative "dense basal rosette of gray-green, rigid, spine-tipped leaves" that span about two feet, according to the Lady Bird Johnson Wildflower Center website. It has a branched radiating root system. It produces, on a single 10- to 15-foot stalk, a dense cluster of purple-tinged, cream-colored, bell-shaped flowers and a juicy, tender but seed-filled fruit. Its blossoms seem to almost glow in the soft light of dawn or sunset, giving the plant its name. Unlike other yuccas, Our-Lord's-Candle dies once it has bloomed.
The Joshua tree yucca, the patriarch of the clan, holds primary residence in the Mojave Desert. Its leaves, according to Richard Katz on the Flower Essence Society website, measure about 5 to 12 inches in length, becoming "sword-like in their intensity" as they mature. Resembling a plant you would expect to find in a Hollywood version of an alien world, a mature Joshua tree has a bizarrely branched stem, a result of its inclination to add new growth from the site of a blossom cluster.
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