Hesperaloe: Aloes of the West

Greg Starr

3340 W.Ruthann Road Tucson, Arizona 85745

Introduction

The genus Hesperaloe (Hesper = western) is small, consist­ing of only five described species. It is widespread with three species occurring on the eastern side of the Sierra Madre Occidental either in or at the margin of the Chihuahuan Desert Region; and the other two species occurring on the western side in the state of Sonora. Each species range is relatively localized apparently without any overlap.

Taxonomy

In the past, plants we now know as Hesperaloe have been referred to the genera Yucca, Agave, and Aloe. Leaves, fruits and seeds are yucca-like, while the pistil has an elongate style as in Aloe and Agave. This combination of characters made placement in a genus difficult. The plants did not eas­ily fit the characters of any of the three genera.

Several authors, including Baker (date unknown), Koch (1862), and Lemaire (1864 and 1866) tried to fit the newly discovered plants into a genus without much success. This problem was solved in 1871 when Engelmann described the new genus Hesperaloe to accommodate Aloe yuccaefolia. In 1894, Coulter determined that Yucca parviflora, described by Torrey (1859), included Aloe yuccaefolia and made the combination Hesperaloe parviflora. Taxonomically this is correct because Yucca parviflora was described before Aloe yuccaefolia.

In 1902, Trelease moved Yucca funifera into the genus Hesperaloe to make the combination Hesperaloe funifera. Sixty-five years later Gentry (1967) described Hesperaloe nocturna from Sonora, Mexico. Recent field work in Mexico has resulted in the discovery of two species that were previ­ously undescribed. Starr (1996) is in the process of describ­ing these two new species from Mexico. The scientific names will be valid when the monograph is published. In the mean­time, their common names will be used throughout this ar­ticle. One species from central Nuevo Leon has a bell shaped flower and is called Bell Flower Hesperaloe. The other is from southern Sonora, has a very narrow leaf and is com­monly called Narrow Leaf Hesperaloe.

There are two basic flower colors for all five species; two species have greenish white flowers and three species have reddish or pinkish flowers. Three species occur in the area between the Sierra Madre Occidental and the Sierra Madre Oriental in Mexico. Two of these species have pinkish or reddish flowers while the third has greenish white flowers. There are two species on the western side of the Sierra Madre Occidental, both occurring in the state of Sonora, Mexico. One species has pinkish flowers while the other has green­ish white flowers.

Flower color may not be all that complex, however, it is interesting that two plants with nearly identical night bloom­ing flowers (H. funifera and H. nocturna) occur on opposite sides of a very large mountain range. Possibly, they could have developed from the same ancestor which may have been more widespread in the past, perhaps 10,000 years ago.

Horticultural Notes

Hesperaloe has been cultivated in the United States since at least 1878 when Krauskopf offered plants for sale that he collected along the western branch of the Nueces River in western Texas. Prior to that, plants were grown at the bo­tanical gardens in Cambridge England from material Wright collected in 1849. All species grow best in full or reflected sun, and a fast draining soil. The faster growing species are H. parviflora and Bell Flower Hesperaloe which flower in four years from seed, and the slower growing species are Narrow Leaf Hesperaloe, H. nocturna, and H. funifera which flower in five years from seed. Hesperaloe has CAM me­tabolism so growth occurs year round.

Growth rate can be increased by fertilizer application and consistent, thorough waterings year round, taking care not to overwater in winter. Amount of fertilizer and water ap­plied will vary with temperature. All species are quite drought tolerant once established. They will survive on less than 12 inches of annual precipitation and can survive for two months or more without supplemental water. They can tolerate some excess water also with H. nocturna growing where it receives 15-20 inches of annual rainfall, and H. parviflora having been grown in areas receiving as much as 50 inches of annual rainfall. No maintenance is required except for removal of old flower spikes if so desired. All species are hardy to at least 15° F, with H. funifera and H. nocturna being hardy to at least 10° F., and H. parviflora hardy to 0° F.

The flowering period for all species is usually longer for cultivated plants than for wild populations. The application of supplemental water and the warmer temperatures of cit­ies versus the open desert results in flower spikes appearing earlier and persisting later in the year. The flowers of H. parviflora are pollinated by hummingbirds as well as bees. Flowers of H. funifera, H. nocturna and Bell Flower Hesparaloe are pollinated by bats and hawk moths. Bell Flower Hesperaloe flowers are pollinated by bats and hawk moths during the night, then the following day they are visited by hum­mingbirds and bees.

Hybridization

Crosses of H. nocturna x H. parviflora (pollen parent unde­termined) and H. parviflora (male) x H. funifera (female) have produced hybrids. F2 offspring from the H. parviflora x H funifera hybrid plants have also been observed. These plants were still young, however, some were of flowering age and did show segregation of flower characteristics back towards the parent species. The progeny of H. nocturna x H. parviflora had the flower color of H. parviflora and flower shape intermediate, while the leaves were more like H. nocturna.

Crosses have been made between Bell Flower Hesperaloe (male) x H. funifera (female) and Bell Flower Hesperaloe (male) x (H. parviflora x H funifera) (female). One could speculate that Hesperaloe funifera and H. parviflora crossed sometime in the past resulting in Bell Flower Hesperaloe, however there are no records of H. parviflora in the vicinity. Flower color and shape of Bell Flower Hesperaloe are con­sistent while leaf size varies. This does not support the theory of a cross, but indicates instead that Bell Flower Hesperaloe is a stable species.

Species Descriptions

1. Hesperaloe species nova #1 Bell Flower Hesperaloe (Figures 1 and 2)

Description: Stemless perennial forming small clumps to 1 meter (3 feet) high and wide. The bright green leaves are 60-100 cm (2-3 feet) long and 1.5 cm (0.6 inch) wide at the widest point above the base. They are stiff and upright to slightly spreading with fine threads along the margins. The flower spike grows to 3 meters (10 feet) tall. It may be un-branched or have 2-5 branches in the upper 1/3. Flowers are tubular-campanulate to broadly campanulate, 20-22 mm (1 inch) long and wide. The backs of the tepals are pink with a white margin; the fronts of the tepals are pure white. This species has a long blooming season, beginning as early as April and continuing into October or November. The woody capsules are 2-3 cm (1 inch) long, 2-2.5 cm (1 inch) wide with a sharp beak to 4-11 mm (0.4 inch) long.

Culture: Plant Bell Flower Hesperaloe only in full or re­flected sun and a rocky, fast draining soil. Plants have a moderate growth rate and respond some to consistent, thor­ough waterings in summer. They are quite drought tolerant once established, surviving on 10-11 inches of annual rain­fall. The only maintenance needed is to remove the flower spike after the blooming period. Plants are cold hardy to at least the low teens (°F).

Identification: Bell Flower Hesperaloe looks like a small version of Hesperaloe funifera when not in bloom. The two species are easy to separate once the flowers appear, Bell Flower Hesperaloe having pink flowers, and H. funifera having greenish-white flowers. Bell Flower Hesperaloe can be distinguished from H. parviflora by the more open flower shape and lighter green, less channeled leaves.

Distribution: Bell Flower Hesperaloe occurs only in a few localities in central Nuevo Leon, Mexico.

2. Hesperaloe species nova #2 Narrow Leaf Hesperaloe (Figures 3 and 4)

Description: An open rosette consisting of few, very nar­row leaves. Plants offset sparingly and resemble a sparse grass. Leaves measure less than 1 cm (3/8 inch) wide, less than 1 meter (3 feet) long and have a thin margin with very fine, white marginal fibers that are not tightly curled. The flower spike is a narrow panicle that appears in late spring and summer. Individual flowers measure 13 mm (1/2 inch) long and 10 mm (3/8 inch) wide. The outsides of the flow­ers are pinkish-red and the insides are white. The flowers are nocturnal, suggesting bat or hawk moths as pollinators. The woody fruit is ovoid to rounded, 2.5-3 cm (about 1 inch) long and 2.5 cm (1 inch) wide.

Culture: Narrow Leaf Hesperaloes are very easily grown. They grow best in soil with good drainage. Plants can be used in filtered sun or with full sun for one-half day. Some supple­mental water is required in summer. Allow the soil to become somewhat dry between waterings to prevent overwatering.

Identification: This species is very easily recognized by its long, very thin leaves with finely textured very curly mar­ginal fibers. When in bloom, it has a very short, open flower that cannot be confused with any other species.

Distribution: Narrow Leaf Hesperaloe is known only from the Cerro Agujudo northeast of Alamos, Sonora. Plants grow on rhyolitic rock on dry hilltops at 1500 m with Pinus oocarpa, Pinus leiophylla and Quercus chihuahuensis.

3. Hesperaloe funifera (Koch) Trelease Giant Hesperaloe (Figures 6 and 7)

Description: Plants are clumping stemless perennials to 2 meters (6 feet) tall and 2 meters (6 feet) across. The 1.5-2 meter (5-6 feet) long, bright green leaves are 3-6 cm (1.5-2 inches) wide with coarse white threads along the margins. They are stiff and straight, not arching, and give the plant an upright appearance. The flower stalk grows to 4-5 meters (12-15 feet) tall. The 2.5 cm (1 inch) long, greenish-white flowers are tinged with purple. The flowering season is mainly in summer, beginning as early as April and ending as late as August. The woody capsules are 2.5-5 cm (1-2 inches) long and contain numerous flat, black seeds.

Giant Hesperaloe is best used in full or reflected sun, and a fast draining soil. The moderately slow growth rate can be increased by consistent, thorough waterings dur­ing the growing season. Plants are quite drought tolerant once established and can survive for two months without supplemental water. No maintenance is required except for removal of old flower spikes if so desired. Plants are hardy to at least 5° F- 10° F.

Identification: The stiff 1.5-2 meter (5-6 feet) long leaves make this species easily identifiable as mature plants. Young plants are difficult to distinguish fromHesperaloe parviflora, how­ever the greener color and stiffer leaves separate H. funifera.

Distribution: Giant Hesperaloe is native to Coahuila, Nuevo Leon, and San Luis Potosi states in Mexico.

4. Hesperaloe nocturna Gentry Night Blooming Hesperaloe (Figure 5)

Description: Very dense, stemless rosettes forming large clumps to 1.5 meters (5 feet) tall and 2 meters (6 feet) across. The narrow, strap-like leaves are 1.5 meters (5 feet) long and 1-2 cm (3/8-3/4 inch) wide at the base, with fine white threads along the margin. These slender, curving leaves and the dense clumping form give the appearance of Bear Grass (Nolina microcarpd). The flower spike grows 1.5-4 meters (5-12 feet) high. Greenish lavender flowers measure 2.4-3 cm (1-1 1/4 inches) long, and are fully open at night. Plants bloom from May through July. Woody capsules are 3-4 cm (11/4-11/2 inches) long and contain many flat, black seeds.

Culture: Use Night Blooming Hesperaloe in filtered, full, or reflected sun. Plants grow best in soil with good drain­age, and with consistent, thorough waterings. They will survive on 10-12 inches of annual rainfall, but the moder­ate growth rate will be speeded when given supplemental irrigation. Plants are hardy to at least 10° F.

Identification: The long, narrow leaves and night bloom­ing flowers make this Hesperaloe easily identified. Night Blooming Hesperaloe could be confused with Clumping Bear Grass (Nolina microcarpa) until either flowers or fruit are seen, both of which are unique to each species.

Distribution: Hesperaloe nocturna is known only from north-central and north-eastern Sonora, Mexico.

5. Hesperaloe parviflora (Torr.) Coulter Red Flowered Hesperaloe (Figures 8 and 9)

Description: A dense rosette of dark green leaves forming clumps to 1 meter (3 feet) across. Leaves are 1-3 cm (1 inch) wide at the base, 0.5-1.2 meters (2-4 feet) long and have thin marginal threads. The flower spike measures 1-2.5 meters (3-8 feet) high with few side branches mainly in the upper one-half. Flower color varies from yellow to salmon or coral through light to dark red. Individual flow­ers are 25-35 cm (1-1 3/8 inch) long. Flower spikes may appear as early as May and continue through October, some­times as late as November or December. The woody fruit is ovoid or globose, about 3 cm (1 1/4 inch) long with a pro­nounced beak, and contains many flat, black seeds.

Culture: Red Flowered Hesperaloe is easy to grow. Plants are tolerant of many soils, preferring one that is fast drain­ing. They achieve their best appearance in full or reflected sun. Plants are extremely drought tolerant once established, surviving on 10 inches of annual rainfall, but will also grow well when given supplemental waterings. I have seen this species planted in lawns in Texas, and growing quite well. Red Flowered Hesperaloe has a moderate growth rate, and is hardy to at least 5° F. Hesperaloe parviflora var. engelmanni is supposed to be hardy to 0° F.

The combination of narrow, salmon-col­ored or rosy-red flowers and relatively short, dark green leaves distinguish this from the other Hesperaloes in culti­vation. There is a form available that has pale yellow flowers.

Distribution: Hesperaloe parviflora is native from central Texas adjacent to Mexico.

Discussion

The New World genus Hesperaloe consists of five species of semi-succulent plants. Species are isolated from each other; and distribution ranges from west-central Texas, to the Mexican states of San Luis Potosi, Coahuila, Nuevo Leon, and Sonora. The leaves are narrow or wide, flat or deeply channeled, straight or arching and have fine or coarse marginal fibers. These fibers are being researched for their potential use in paper products.

The flowers occur on short to tall stalks that are either un-branched or with as many as eight lateral branches. Indi­vidual flowers are tubular, bell shaped, or rotate. Flower color is either greenish white, yellow or various shades of red, pink, or salmon. Flowers are pollinated by bats, hawk-moths, bees, or hummingbirds.

Each species is suitable for landscaping in the warmer parts of the southwestern United States. As a whole, plants within the genus are drought and sun tolerant, cold hardy and re­quire very little maintenance. They can be used singly as an accent plant or grouped together for an effective mass plant­ing. Hybrids have been known to occur and offer many pos­sibilities for development of some interesting landscape plants. However, it may take several years to develop a hy­brid Hesperaloe with potential in the landscape trade.

Acknowledgments

I thank Dr. Steve McLaughlin for his encouragement and manuscript review, and for sharing his extensive knowledge of Hesperaloe. I thank Mr. Ron Gass for his enthusiasm in the field and continued support throughout this project. I also thank Dr. Charles Mason for his taxonomic help and manuscript review. My thanks go out to Dr. Richard Felger for scrutinizing the manuscript. Thank you also to Dr. George Yatskievych for his tireless research into the tax­onomy of H. funifera.

Literature Cited

Baker, J. G. n.d. On Aloineae and Yuccoideae. Journal of the Linnean Society of Botany. 18: 228.

Coulter, J. M. 1894. Botany of Western Texas. Contribu­tions from the US National Herbarium. 2: 588 pp.

Engelmann, G. 1871. in S. Watson Botany of the 40th Parallel. 5: 497.

Gentry, H. S. 1967. A new Hesperaloe from Sonora, Mexico. Madrono 19(3): 74-78.

Koch, K. 1862. Exposition quinquennale de plantes et de fleurs Belgique Horticole. 12: 107-133.

Krauskopf, E. 1878. Notice to Botanists, Botanical Gardens and Nurserymen. Circular.

Lemaire, C. 1864. Especes Nouvelles D'Agave. Illustration Horticole. 11: 63-66.

Lemaire, C. 1866. Du Genre Yucca. Illustration Horticole. 13: 90-102.

Starr, G. 1996. A Revision of the Genus Hesperaloe (Agavaceae). Madrono, in ed.

Torrey, J. 1859. Botany of the Boundary; Emory's Report of the US - Mexican Boundary Survey. 29-270.

Trelease, W. 1902. The Yucceae. Report of the Missouri Botanical Garden. 13: 27-31.

© Desert Life, 1995