Yuccas are a genus of plants that are much under used and under appreciated in the home landscape. They are often associated with dry desolate looking native landscapes or poorly conceived xeriscape yards. Yuccas are easy care, drought tolerant natives that will provide a distinctive and interesting evergreen element to many home landscapes.
Yuccas are perennial, evergreen, shrubs native to North and Central America and the Caribbean Islands with about 50 known species. Mexico is the diversity center for yuccas. About 20 species of yucca can be found growing in Texas’ diverse eco-regions from the Gulf Coast, the Piney Woods, Edwards Plateau, Blackland Prairies and Cross Timbers region to Big Bend and West Texas all the way to the Rolling and High Plains of Texas. Yucca are native to both hot humid areas of southeastern U.S. from New Jersey to Florida, west to east Texas. Many more species are native to the hot, arid, and semi-arid climates of Central and West Texas, from the desert floor to as high as 8500 feet in elevation in southern Colorado, Nevada and Utah. Yuccas can be found in every desert region in North America. Yucca glauca’s range extends even into the southern plains of Canada. Western species are found natively in gravely, rocky or sandy soils, on the plains and slopes, shrublands and grasslands of the high desert. The yuccas of the eastern U. S. are found mostly in sandy and gravelly soils and on beaches or sandy coastal areas that drain quickly. (Photo at left is of Yucca thompsoniana in the foreground and Y. rostrata to the upper right in the frame; photo at left is Y. harrimaniae.)
Yuccas quickly became an important ornamental plant in cultivated gardens as early as the sixteenth century. Yucca is the native Caribbean name for cassava, (Manihot esculenta). Linnaeus named the genus Yucca in 1753, mistakenly deriving the generic name from the local Caribbean language for yuca (spelled with a single "c"). Yuccas are now classified in the subfamily Agavoideae, and the larger family, Asparagaceae, according to the Angiosperm Phylogeny Group III (2009). Due to their tolerance to differing conditions and soils, many yuccas are used ornamentally throughout the United States and across the globe.
The remarkable nature and usefulness of yuccas have caused them to be ennobled in place names. Both a national park, Joshua Tree National Park and a monument, Yucca House National Monument preserving one of the largest archeological sites in SW Colorado, are named after a yucca species, Yucca brevifolia, and the genus yucca. (Yucca House National Monument is actually named after a place, “mountain with lots of yuccas growing on it”.) There is a Yucca Valley incorporated town in California, an unincorporated town, Yucca, Arizona, and Yucca Mountain in Nevada. Photo at right is of Y. brevifolia, the Joshua Tree yucca.
Few yuccas are succulents, yet many succulent enthusiast grow yuccas. Yuccas that are not succulent have thin leaves and deep roots, like the Soaptree yucca, Yucca elata. Even though most yuccas are not succulent, they are often listed along with most other succulent plants because of their xeriphytic nature.
Succulents are plants that store water in one or all of three organs in the root, stem or leaves. Nearly all succulents have extensive, very shallow root systems that are adapted to absorbing lots of water after very light rainfalls. Most of them use their stored water to continue metabolic activity when there is no available water in the soil. That is, they may grow during the dry season.
In order to be able to do the above two functions, many succulent and non-succulent plants have a special variant of photosynthesis called CAM. CAM plants are ten times more efficient with water consumption than non-CAM plants. This is very important where water is scarce. Plants that photosynthesize with CAM can withstand hotter conditions as well as dry. All yuccas photosynthesize using CAM.
Most yuccas are xeriphytic – that is able to grow under dry and often hot environments. Most species of yucca have thick, waxy skins to prevent loss of water through evaporation. They frequently store water in thick roots and some yuccas store water in thick, fleshy leaves. Their leaves also serve another function – dead leaves that hang down protect the stem/trunk of the yucca from heat and evaporation and absorb moisture during hard desert rains. Photo of a grouping of Yucca faxoniana at left.
Physical Characteristics of Yucca
Yuccas come in many forms, from small clumping or non-clumping grass-like rosettes, trunked plants (treelike), either branched or unbranched up to thirty feet tall. Smaller trunkless species are usually found growing in colder regions, such as Yucca baccata (photo left) in high desert areas, and the plains yucca, Yucca glauca (photo on the right), which grows as far north at lower Canada in the Great Plains. Arborescent yuccas inhabit warmer subtropical and tropical regions, either humid or arid. Yucca elephantipes is one example of a yucca native to a tropical area in Mexico southward to Guatemala, and Yucca filifera, growing in hot semi-arid climates requiring minimum temperatures above 20-25°. Trunks are usually upright, but in some cases can run along the ground making the plant appear trunkless. The “wood” of the trunks are fibrous, containing air spaces, making them strong and light weight.
The leaves vary in thickness, length, width and color from yellow-green, blue-green to green, either glaucous (covered with a blush or waxy bloom, appearing whitish green or blue), glabrous (smooth and without hairs) or scabrous (rough). Leaves are fibrous, half the species with filaments peeling from the margins, serrated or smooth, most terminating in a spine that is either very pointed and sharp, thick to blunt. Leaf margins may have an identifying thin stripe colored yellow, brown or brown and white. The leaves can be either stiff and rigid, held upright and/or outward, or quite limp and flexible that hang downward like Y. recuvifolia and Y. flaccida. Some yuccas have leaves that are flat, curled inward, or nearly rounded; some yuccas with many leaves up to a hundred, or just 15-20 to a head. Leaves may also remain on the plant and hang downwards when dead the entire life of the plant; a few will shed their leaves. Yucca glauca flower at right.
Most yuccas are polycarpic, but do not bloom every year, as it requires much energy to produce the fruits. Commonly, after a year of abundant blooms, it will not bloom the next year. Most yuccas flower in April or May, only a few flower in June or July. About half of all yucca species form woody capsules similar to other members of the former subfamily Agavaceae. The others form large fleshy fruits that were eaten by indigenous peoples and animals. The flowers of the yucca are mostly bell-shaped, having three sepals and three petals, more similar to tepals, and the sepals and tepals can either be similar or slightly dissimilar to each other. Tepals are white, creamy white to greenish white in color and thick and leathery in appearance. The inflorescence is either a raceme (unbranched) or a panicle (branched) with the flowers on the stalk held either entirely within the leaves, mid-way within the leaves, or held high above the rosette on a tall stalk. Yucca glauca flowers at left.
Pollination and Importance of Yuccas
Yucca pollination ecology is an example of a tight symbiosis called mutualism, where each species depends on each other for survival. Yuccas are pollinated by small whitish moths in the genera Parategiticula and Tegiticula, except for Yucca aloifolia, which is pollinated by bees. Sometimes just one moth species is the pollinator of one yucca species, in some cases, yuccas can be pollinated by several moth species. Yucca species are the host plants for the caterpillars of the yucca giant-skipper, ursine giant-skipper, and Strecker's giant-skipper butterflies.
Yuccas are the work horses of the xeric landscape, providing food, shelter and habitat for a plethora of animals and Native Americans. They are built tough enough to survive the extremes of drought, cold and heat from desert floor to arid mountains, able to withstand the blazing sun and frigid nighttime temperatures, all within the same 24 hour period. Yucca plants were extremely useful to indigenous peoples in many ways. They used yucca in basketry, bowstrings, brushes, cordage, dye, fruits, mats, needle thread, netting, paper, sandals, soap, and food (young emerging stalk, flowers, fruits and seeds).Yucca provides important hunting, roosting, and nesting sites for birds and food, nest materials, nesting sites, and habitat for reptiles and small mammals. Deer, elk and rabbits forage young leaves, new flower stalks and/or flowers. Photo at right is flower stalk of Yucca pallida x rupicola. Young tender stalks are said to taste like asparagus. It is easy to note yucca's inclusion in the Asparagaceae family.
Growing Yuccas on the Texas High Plains
Nearly half of the known yucca species can be grown in ground in most of the Texas Panhandle. Yuccas make terrific multi-purpose plants for the home landscape of the Texas High Plains whatever the water zone, as an accent specimen plant and for contains. Yucca’s native to the east and southeastern United States, including east Texas, integrate well into the higher water zoned beds. Yuccas native to the southwest in dry hot regions and in higher mountain elevations provide a needed evergreen presence in xeriscape and native plant beds. The arborescent, or tree-like yuccas, are natural architectural focal points. As most yuccas are native to hot and arid regions, they naturally connote a sense of place, while providing stunning winter interest, with or without snow. And many of both cold hardy and non-hardy yuccas make great container specimens, when properly protected in the winter months inside. Photo of Yucca pallida at left in foreground and Y. baccata behind it.
Yuccas are easy to grow and carefree plants for the low maintenance landscape. Yucca’s prefer full sun, but will grow just as well in part sun. The southeastern yuccas can take part shade, but should have 4-6 hours of sun for flowering. Yuccas transplant easily from containers, and can be readily moved when young.
Establishment is quick, requiring only weekly watering initially, less for subsequent months the first year. In subsequent years, native southwest yuccas will thrive quite well on available rainfall, except in drought years. During drought, water an inch of water every month. Yuccas native to the east and southeastern United States might require irrigating every other week during drought years. Most yuccas grow natively in soil that has good to very good drainage. In heavy clay soil, yuccas still grow well, although it is important not to over water. Particularly, I’ve had top growth of Yucca filamentosa varieties die when watered during cold and dry Februaries, however, they’ve always grown back. I’ve learned its better not to water them in February at all.
Several years growth are required before yuccas flower. Yuccas in containers may not flower at all, or take a many years to flower. I’ve not ever had a variegated variety of Y. filamentosa flower, such as ‘Gold Sword’, or ‘Color Guard’ flower, or the variegated Y. aliofolia. Photo at right in container is Y. gloriosa marginata.
24 Yucca Species for the Texas Panhandle Landscape
Yucca aloifolia, Aloe yucca, Spanish dagger. Single stemmed or simple branched yucca grows to about 10 ft. Leaves are 12-20 inches long and one to one and a half inches wide with small sharp teeth along the edge. Leaves are tightly arranged around the stem. The inflorescence (flower) is a panicle 1 – 1.5 feet long with three quarters of the panicle rises above the leaves. This yucca was the first yucca in cultivation in North America and in the Old World, as early as 1605. It’s natural range is from Virginia to Florida to Louisiana and the Caribbean Islands. Many different varieties including variegated and will grow in a variety of garden conditions and soil. Yucca aloifolia variegata is a preferred variety. Cold hardy to 0°. Photo at left.
Yucca arkansana, Arkansas yucca, soft leaf yucca. Trunkless evergreen shrub with bluish to yellowish green 8-24 inch leaves arising from non-symmetrical basal rosette, sharp pointed, with curly white fibers on the margins. Leaves often have a twisted and frayed appearance. Inflorescence is unbranched rising to 2-6 (usually 2-3) feet in height. Greenish-white flowers appearing from April to June. Native to Texas, Oklahoma and Arkansas. Cold hardy to -10°.
Y. baccata, banana yucca, Blue yucca, Datil yucca. (Photo right.) Small trunked species with one to ten trunks forming clusters to 16 feet wide. Deeply concave blue-gray leaves grow to 2 ½ feet long and 2.25 inches wide with numerous filaments along the margin ending in a strong, sharp spine. The flowers are on a branched panicle with less than half rising above the leaves. The flowers are creamy white edged with maroon. Y. baccata var vespertina has solid maroon stalk and flowers. Very large range from West Texas, southwestern Colorado, most of New Mexico, Southern Utah and southern Nevada and most of Arizona, as well as northern Mexico. Cold hardy to -20°.
Y. brevifolia, Joshua Tree. The largest yucca tree-form grows up to 30 feet or more, and rarely up to 50 feet tall and can spread 30 feet wide. Although many branched and tree-like in appearance, branches bend at right angles or downward. The light green to blue-green leaves are rigid, 6-14 inches long and half inch wide and are tightly arranged at the end of a branch. The leaves have minute teeth along the edges and end in a sharp point. Old leaves hang down covering the trunk, but after many years, the trunk becomes exposed revealing a plated pattern. The inflorescence is a panicle with cream to greenish white flowers densely amassed, barely opening, emitting an unpleasant odor. The Joshua Tree is the indicator plant of the Mojave Desert in elevations from 1500 – 6500 feet, but can be grown widely because of its cold hardiness, down to -10°. Joshua Tree National Park is named after this unique yucca. Flower of Yucca brevifolia at left.
Yucca campestris, Plains Yucca. Small, clumping, usually stemless, but also stemmed, evergreen yucca to 3 feet tall. Leaves are blue-green, slender and wiry less than 3 feet in length. Young plants have fine white filaments along the margins but grow smooth with age. The inflorescence is a panicle that usually does not rise above the leaves. The flowers are a dull green with a pink tinge on a stalk up to 6 feet in a mature clump. Native to deep sands in Howard, Ector, Midland and Ward Counties of Texas, where it is endemic. Cold hardy to Zone 7.
Yucca constricta, Buckley’s Yucca. Buckley’s yucca is a trunkless evergreen of the Texas Hill Country and south to the coast and Rio Grande plains, its range extending east towards Houston and Dallas. The bright green leaves are long (up to 25 inches), narrow (half an inch), thin and flexible, lacking both terminal spines and (usually) white filaments. Greenish white flowers reach upwards to five feet. Said to be difficult to transplant due to a long taproot. May not be cold hardy in the Texas Panhandle – cold hardy to Zone 8.
Y. elata, Soaptree Yucca. Soaptree yucca can have populations that are all stemless, or trunked and branched, usually with 1- 10 trunks. It commonly grows 6-15' tall, but can grow as tall as 30 feet in ideal conditions. The dullish green leaves are densely arranged in a radial head, thin and flexible up to 3 ft. long and very narrow at a quarter inch wide with white filaments along the margin. The inflorescence is a large open panicle 3-7 feet tall with the white to greenish white flowers held high aloft from the leaves. Mature plants can bloom up to twenty stalks. This spectacular show may be the reason it is the state flower of New Mexico. Soaptree yucca is native to the high deserts and desert grasslands of southwestern U. S. in New Mexico and Arizona in elevations from 2000-5500 ft. It’s temperature versatility and stunning floral show inspire its use ornamentally. Soaptree yucca gets its name from the saponin in its roots and stems where a soap was made by indigenous peoples and settlers. It is cold hardy to -10°.
Y. faxoniana, Faxon's Yucca, Giant Dagger Yucca. (Photo right.) A large arborescent yucca grows 6-20', usually single but can be multi trunked, nearly always unbranched. Dark yellow-green leaves grow 2-4 ft. long and 2-3 inches wide, dark brown stripe along the leaf margin with curling white filaments, ending in a dark brown terminal spine. The rigid leaves are arranged symmetrically and remain attached hanging down when they die. The greenish white flower is a panicle 3-4 ft tall with 25-40 branches and is held completely above the leaves, or with no more than a quarter within the leaves. Native US range is west of the Pecos in Texas, and south to San Luis Potosi in Mexico. Named after Charles Faxon, a botanic illustrator. Cold hardy to 0°.
Y. filamentosa, Adam’s needle. Trunkless clumping species that readily offsets. The rosette can grow up to 4 feet wide. The leaves are thin and flexible, generally straight at the head, with abundant filament curling along the margins. The inflorescence is held well above the leaves from 4-15 feet. The flowers are white or cream, sometimes tinged with pink or brown. Native to the South Atlantic and Gulf coastal plain from Florida to Mississippi and north to New Jersey. Needs medium water-use, benefits from afternoon shade. It’s use in cultivation dates back to the seventeenth century in Colonial and British gardens. Many varieties including 'Color Guard','Gold Sword', ‘Bright Edge’, 'Bright Lights', 'Blue Sword', ''Hairy”. Cold hardy to -20°. Photos at left, summer and winter, Y. filamentosa 'Hairy'.
Y. flaccida. A small, stemless clumping species grows up to 3 feet tall and 5 feet wide. The green leaves are about 2 and a half feet long and a half inch to inch and a half wide, lanceolate, recurved and flaccid throughout the entire head with straight, fine long filaments. The inflorescence is 4-7 feet tall and blooms only slightly above the leaves. The creamy white flowers are in broad open clusters and lightly fragrant. Yucca flaccida has many natural and horticultural variations and is close in appearance to Y. filamentosa , however they are separate species. Yucca flaccida is native to the southern Appalachian Mountains from western North Carolina to Northern Alabama. It has a wide use in ornamental gardens, both here and abroad due to its cold moisture tolerance; down to -20°.
Y. glauca, (aka Y. angustifolia) Soapweed yucca, Plains soapweed. Mostly a stemless species but can have short prostrate branching trunks. Leaves are 8-36 inches in length and a quarter to a half inch in width, gray-green, narrow with thin white marginal stripes, filaments along the margin. The inflorescence is a spike 3-6 feet tall and held aloft from the leaves. Flowers are greenish white, pendulous, bell shaped and fragrant. Our area native grows as far north as Canada. It’s main drawback is its invasiveness. Cold hardy to -35°. Photo at right.
Y. gloriosa, Mound lily or Soft-tipped Yucca. Mostly a simple arborescent species, but can be branched, growing from 6- 15 ft. tall. The light green leaves usually are straight, but can be reflexed in the middle or near the end, thin and pliable, 13-20 inches long and one and a half to two inches wide with minute serrations and a spineless tip. The inflorescence is on a narrow stalk 2-4 feet with the panicle partially within the leaves. White flowers are 1 and a half to two inches long, occasionally tinged with purple or red. One of the few yuccas that blooms outside of spring, from mid to late summer, sometimes in the fall. Native to the Gulf Coast, along the coast and north to South Carolina. There is much variation within the species and can be grown nearly anywhere where it’s warm enough. Y. gloriosa marginata is an attractive variety. Cold hardy to 22°, other sources down to 0°; makes a beautiful container plant, regardless.
Y. harrimaniae, Harriman's Yucca. (Photo left.) Very short and small, usually not more than 12 inches tall. Stemless rosettes or short stems from 8-36 inches wide, either single rosettes or clumped. The leaves are variable in size and color, 4-18 inches long and yellow to blue green, are stiff, yet bendable, concave rather than flat, with a brown marginal stripe, white filaments. The inflorescence is a raceme (unbranched inflorescence) from 1-3 feet tall with greenish white flowers. Native to northern Arizona, and New Mexico and southern Utah and Colorado, generally at an elevation of 7500-8500 ft. Cold hardy to -20°.
Yucca louisianensis, (Syn. Yucca arkansana var. paniculata, Yucca freemanii) Louisiana Yucca, Gulf Coast Yucca. Small evergreen yucca 2-3 feet tall and 3-5 feet wide. Leaves are two feet long and ½ – ¾ inch wide, limp, dull green leaves usually bear whitish threads along the margins and a sharp point at the end. Inflorescence is a pubescent (downy) flower stalk with greenish white flowers rising to 9 feet. Native east of the Blackland Prairies in Northeast Texas, usually in dry sandy uplands. It is most common in Louisiana and ranges somewhat into Arkansas and Oklahoma. Cold hardy to Zone 7.
Y. pallida, Pale leaf Yucca. An acaulescent (stemless), clumping species 7-20 inches tall by 12-32 inches wide. Leaves are pale blue-gray, 6-16 inches long and three quarters to an inch and a quarter wide, widest at the midpoint. Leaves are generally flat, lined with minute teeth and a thin yellow to brown marginal stripe that terminate in a yellow to brown spine. The inflorescence is a panicle 3-7.5 ft. tall with many pale green to cream colored flowers with a lighter colored margin. The stalk first emerges red and then fades to green and blue-green. Native to Blackland prairies of Texas and the Edwards Plateau. Cold hardy to at least 0°. Hybrid cross Y. pallida x rupicola yields a pale twist leaf yucca – very attractive.
Y. recurvifolia, (aka Y. pendula), Curved Leaf Yucca, Soft Leaf Yucca. (Photo at left.) Trunked species to 6-10 ft. tall and will form multiple trunks that can curve and bend at odd angles. Flat, dark blue-green leaves are 2-3 ft. long and 2 wide with a lax and recurved habit with a thin yellow or brown margin stripe. The inflorescence is a large, loose open panicle 3-5 ft. tall with many stalks to a mature specimen. Flowers are cream colored. Native to the South Atlantic and Gulf Coast Plains in Georgia, Mississippi and Louisiana. Very versatile for the home garden with several varieties. 'Yellow Ribbons' is a new variety. Curved Leaf yucca lines the fence in the California Garden. Cold hardy to 0°.
Yucca reverchonii, San Angelo yucca. Could be a natural hybrid between Y. thompsoniana and y. rupicola. A small evergreen usually trunkless (very short trunk in old age), non-clumping plant grows to 2-3’ tall and wide with thin blue-green leaves and a yellow serrated margin. Flower is greenish white with the non-branching inflorescence rising up to 5-8 feet. Native to the Edwards Plateau of Texas, perhaps only cold hardy to Zone 7B.
Y. rigida, Blue Yucca. A medium sized, single trunked species with multiple stems to 15 feet and occasionally branched. Very attractive light blue-gray leaves are rigid and narrow growing 2-3 feet in length and I inch wide. Their attractiveness is enhanced by a yellow margin with minute teeth. The leaves form a half sphere on top of the stems, with dead leaves hanging down covering the trunk. The inflorescence is a panicle 2 feet tall and is partially hidden by the leaves. Flowers are creamy white and close to the stalk. Blue yucca is native to the northern states of Mexico, but is planted ornamentally throughout the Southwest and grows well in a container in colder locations. Closely related in appearance to Y. rostrata. Cold hardy to 5° (Zone 7b).
Y. rostrata, beaked yucca. (Photo at right.) Very similar to Y. thompsoniana and Y. rigida. Single trunked with multiple stems, grows 6-15 ft. tall. Light blue, thin leaves form near hemispherical heads 16-24 inches long and a half inch wide and can have a slight twist or bend to them. The inflorescence is a panicle 2 ft. long usually raised completely above the leaves. The flowers are bright white. Native to Brewster County Texas and south into Coahuila and Chihuahua in Mexico. Cold hardy to 5° (Zone 7b).
Y. rupicola, Twist Leaf Yucca. (Photo at left.) Small, stemless, clumping species 10-30 inches tall to 1 and a half to 4 ft. wide. Bright olive green leaves that twist and arch are 8-24 inches long and a half inch to two inches wide, edged with minute teeth and a thin red, orange or yellow marginal stripe with a short terminal spine. The inflorescence is an open, branched panicle to 5-9 feet tall, red when it first emerges. White to greenish white flowers are long and pendant. Native to the Edwards Plateau in a limited natural distribution area. Cold hardy to 0°.
Y. schidigera, Mohave yucca. A branched, single and multi trunked arborescent species grows 3.5 – 16.5 feet tall. The yellow-green leaves are rigid, growing from 1 – 4 feet long (usually 2 feet) and half inch to one and a half inch wide, curling, white filaments lining the margin and ending in a terminal spine. Mojave yucca is native to the Mohave Desert and northern Baja California. Very heat and drought tolerant, and is cold hardy to 0°.
Y. schottii, Mountain Yucca. Simply branched, medium single trunked to 6-15'. The straight and rigid leaves are blue-green to gray green, smooth and shiny, 1.5 – 3 feet long and one to two and a half inches wide. The leaves are concave with a thin brown stripe and end in a light brown terminal spine. The inflorescence is a nodding panicle 1 – 2 ¾ feet long and is held partially above the leaves. The white flowers are spherical cup-shaped. Mountain yucca grows natively in the foothills and mountains of southeastern Arizona, southwestern New Mexico and northern Mexico in elevations from 4000 - 7000 ft. Mountain yucca can tolerate more moisture than the more desert yuccas and makes an attractive addition to home landscapes. Can tolerate shade. Cold hardy to -10°.
Y. thompsoniana, (aka Y. rostrata), Thompson’s Yucca, Beaked Yucca, Big Bend Yucca, Soyate and Palmita. Treelike, usually with a single trunk up to 12 feet. Symmetrical narrow I/2 inch, stiff leaves are attached to trunk. The leaves are fine toothed with a pale yellow margin and end in a spine. Named after Charles Thompson, agave specialist at the Missouri Botanic Garden in the early twentieth century. A neat and trim appearance for the home landscape. Native to Brewster Co., TX and south into Coahuila, Mexico. Temperatures down to 0° to -10°.
Y. torreyi, Torrey yucca, Spanish Dagger, Old Shag. Treelike up to 24', but usually only to around 6 ft north of Mexico. Leaves are held upright and are rigid, but fleshy 2-4 ft. long and taper to sharp spines with loose course fibers curl along the edges. Large bell shaped creamy white flowers hang from a short stalk off of branchlets in dense clusters. The panicle is held aloft at least halfway above the leaves. Somewhat untidy and shaggy in appearance. It’s native range is in the upper Rio Grande Plains, the Edwards Plateau through the Trans-Pecos regions of Texas and southern New Mexico. Named after John Torrey, botanist. Cold hardy to 5° (Zone 7b). Photo at right.
Closely related to Yuccas
I give mention here to two species that are regularly considered to be yuccas, but are not in the Yucca genus. They are classified in the Hersperaloe and Hesperoyucca genera.
Hesperaloe parviflora, Texas Red Yucca, Aloe Yucca, Red Hesperaloe. (Photo at left.) A stemless species of hesperaloe, and the only one cold hardy in the Texas Panhandle. Single rosettes grow to 3-4 feet wide, and clumping, up to 6 feet or so. Dark olive green leaves and thin, hard and linear growing quarter inch to half inch wide and up to four feet long with white curling filaments from a smooth margin. The leaf edges curl inward along the leaf giving a rounded appearance. The inflorescence is a raceme 5-9 feet tall or a loose open panicle that rises above the plant. The raceme can be quite short in some plants. Flowers are tubular and open irregularly along the stalk, opening during the day and closing at night continuously through the summer, April to October in warmer climates. Flowers are carmine red, to coral and pink. True red and yellow varieties are also available. Texas Red Yucca grows sparsely in western Texas and more abundantly in northeastern Mexico. It's red flower and continuous bloom season have made it a favorite ornamentally throughout the Southwest and beyond. It's cold hardy to -20°.
Hesperoyucca whipplei, Our Lords Candle, Chaparral Yucca, often shown as Yucca whipplei. This plant looks very much like many yuccas, but due to slight differences, it has been deemed the differences are significant enough to warrant a different genus. Chaparral yucca grows as a single rosette or clumped, 2-3 feet wide singly and in clumps, up to 3-6 feet wide. Long bluish to gray green leaves are rigid, 1 3/4 ft - 3 feet in length and half inch to three quarter inch wide with a three sided appearance, ending with a sharp point. The inflorescence is unique, rising to 13 feet tall with a highly branched panicle with hundreds of flowers. Flowers are white and purple tipped. The rosettes take many years to reach maturity, over 50 year. Chaparral yuccas, unlike the other true Yucca species, are monocarpic -- blooming only once and then dying. When it does bloom, the prolific amount of blooms creates quite a show. Hesperoyucca whipplei is native to Southern California and Baja California of Mexico. It's rated cold hardy to 0°. Photo of flowers at left and plant in bloom at the left.
Information taken from the following sources:
Agaves, Yuccas and Related Plants, A Gardener’s Guide, Mary and Gary Irish, Timber Press, 2000.
How to Grow Native Plants of Texas and the Southwest, by Jill Nokes, University of Texas Press, revised and Updated, 2001.
Little Big Bend, Common, Uncommon and Rare Plants of Big Bend National Park, by Roy Morey, Texas Tech University Press, 2008.
Wild Plants and Native Peoples of the Four Corners, by William W. Dunmire and Gail D. Tierney, Museum of New Mexico Press, 1997.
Lady Bird Johnson Wildflower Center, Plant Data Base website
Wikipedia and various other websites.
Angie Hanna, August 2, 2016
(Y. pallida at left, Y. recurvifolia at right; two excellent garden companions.)