Yucca arizonica McKelvey is the tree-forming banana yucca — the only member of the Yucca baccata complex that develops a true, branching, above-ground trunk. While the typical Yucca baccata is acaulescent or nearly so, hugging the ground as a low rosette or sprawling clump, Yucca arizonica stands upright: a stocky, arborescent plant with thick trunks to 1.2–2 m crowned by dense rosettes of broad, boat-shaped leaves. It is the iconic yucca of the Sonoran and Chihuahuan desert transition zone in south-eastern Arizona and south-western New Mexico, where it grows on rocky slopes and desert grassland at 900–1,800 m elevation. The Flora of North America and POWO treat it as Yucca baccata var. brevifolia L.D. Benson & Darrow — a mere variety of the banana yucca. But in the field, in the nursery and in the garden, it is a profoundly different plant from the acaulescent, ground-hugging var. baccata, and it circulates in the specialist trade under its own names: Yucca arizonica, Yucca thornberi, or Thornber Yucca.
This page treats Yucca arizonica as a distinct horticultural entity — as it is understood by specialist growers and sold by specialist nurseries — while explaining the taxonomic situation in full. It should be read alongside the species page on Yucca baccata, the hub page on the genus Yucca and the broader agavoids guide.
The taxonomic situation
The nomenclatural history of this plant involves no fewer than five names applied to the same entity, making it one of the most renamed yuccas in the genus.
Chronology of names
| Name | Author | Date | Status (POWO) |
|---|---|---|---|
| Yucca brevifolia Schott ex Trel. | Trelease | 1902 | Nom. illeg. (not Engelmann 1871, which is the Joshua tree) |
| Yucca treleasei J.F. Macbr. | Macbride | 1918 | Nom. illeg. |
| Yucca thornberi McKelvey | McKelvey | 1935 | Synonym of Y. baccata var. brevifolia |
| Yucca arizonica McKelvey | McKelvey | 1935 | Synonym of Y. baccata var. brevifolia |
| Yucca confinis McKelvey | McKelvey | 1938 | Synonym of Y. baccata var. brevifolia |
| Yucca baccata var. brevifolia L.D. Benson & Darrow | Benson & Darrow | 1943 | Accepted name |
| Yucca baccata subsp. thornberi (McKelvey) Hochstätter | Hochstätter | 2001 | Synonym of Y. baccata var. brevifolia |
The tangle arose because Trelease in 1902 used the name Yucca brevifolia for this Arizona plant — a name already occupied by Engelmann’s 1871 Yucca brevifolia, the Joshua tree. Trelease’s name was therefore illegitimate. Macbride’s replacement name Yucca treleasei (1918) was also illegitimate (as a later homonym conflicting with Sprenger’s 1906 use). McKelvey then published two names — Yucca thornberi and Yucca arizonica — in 1935, treating them as distinct species, along with Yucca confinis in 1938. Finally, Benson and Darrow in 1943 reduced the entire complex to a single variety: Yucca baccata var. brevifolia. This is the treatment followed by the FNA and POWO.
The current consensus
| Authority | Treatment |
|---|---|
| POWO (Kew) | Synonym of Yucca baccata var. brevifolia |
| Flora of North America | Synonym of Yucca baccata var. brevifolia |
| Llifle (Encyclopedia of Living Forms) | Accepted name: Yucca baccata var. brevifolia |
| Espejo Serna & López-Ferrari (1993) | Cited as Yucca arizonica (accepted at species rank) |
| Hochstätter (2001) | Yucca baccata subsp. thornberi (subspecific rank) |
| Horticultural trade (Plant Delights, specialist nurseries) | Sold as Yucca arizonica or Yucca thornberi |
What this page follows
This page treats Yucca arizonica as a recognisable horticultural entity corresponding to the arborescent, trunk-forming populations of the Yucca baccata complex from south-eastern Arizona and south-western New Mexico. This is the plant sold by specialist nurseries under the name Yucca arizonica or Yucca thornberi. For the POWO-compliant species treatment — including the acaulescent var. baccata and the former var. vespertina — see the species page on Yucca baccata.
Taxonomy
| Family | Asparagaceae |
| Subfamily | Agavoideae |
| Genus | Yucca L. |
| Subgenus | Yucca (fleshy-fruited) |
| Species (as treated here) | Yucca arizonica McKelvey (1935) |
| POWO-accepted name | Yucca baccata var. brevifolia L.D. Benson & Darrow (1943) |
Common names: Arizona Yucca, Thornber Yucca, Thornber’s Yucca.
The epithet arizonica refers to Arizona, the heart of the plant’s range. The name thornberi, often used interchangeably, honours John James Thornber (1872–1962), a pioneering botanist of the University of Arizona who made extensive plant collections in the Sonoran and Chihuahuan deserts. McKelvey published both names in the same year (1935) in the Journal of the Arnold Arboretum, volume 16 — thornberi on page 268 and arizonica on page 270.
Why treat it separately from Yucca baccata?
The morphological gap between var. baccata and var. brevifolia (= Yucca arizonica) is the widest infraspecific variation in the entire genus Yucca. The two entities differ in habit, stature, branching, leaf margins and inflorescence position — essentially every character that a gardener uses to evaluate a plant:
| Character | Var. baccata (typical banana yucca) | Var. brevifolia (= Yucca arizonica) |
|---|---|---|
| Habit | Acaulescent or short-stemmed; stems 1–6, aerial or subterranean, shorter than 0.3 m | Caulescent; stems 1–24, aerial, often branched, some reaching 2 m |
| Overall form | Low, ground-hugging clump; wider than tall | Upright, tree-form; thick trunks topped by rosette crowns |
| Leaf margins | Coarse, curling fibres | Filiferous — fine, thread-like filaments |
| Inflorescence position | Arising within or extending ¼ beyond the rosette; peduncle 0.6–0.8 m | Arising almost completely within to mostly extending beyond the rosette; peduncle to 0.3 m |
| Distribution | Entire species range: AZ, CA, CO, NV, NM, TX, UT, Chihuahua | Restricted to Arizona and New Mexico |
| Habitat | Rocky slopes, piñon-juniper, desert grassland; 400–2,500 m | Moist regions; undeveloped soils with mixed grasses and desert shrubs; 900–1,800 m |
| Garden impression | A ground-level rosette plant | A small tree or large shrub with a trunk |
These are not subtle differences. A garden containing a clump of var. baccata and a trunked specimen of Yucca arizonica would appear to hold two completely different plants. This is why the horticultural trade persists in separating them, regardless of the POWO synonymy.
Morphology
Yucca arizonica is a stocky, arborescent, branching yucca reaching up to 2 m (occasionally more) in height. It is the only truly tree-forming entity within the Yucca baccata complex. The trunk is thick — noticeably stout relative to the plant’s height — clothed in persistent dead leaves and often branching to produce multiple heads, each bearing a dense terminal rosette. Mature specimens can have up to 24 aerial stems, though garden specimens typically have fewer.
The leaves are broad, rigid, concave (boat-shaped in cross section), blue-green to grey-green, tipped with a stout spine. They are similar in dimension to those of var. baccata (50–76 cm long, 2.5–5 cm wide) but differ crucially in their filiferous margins — the edges bear fine, thread-like filaments, whereas var. baccata has coarse, curling fibres. This character is easily observed in the field and in the garden.
The inflorescence arises almost completely within the rosette or extends mostly beyond it, on a peduncle to 0.3 m — shorter than in var. baccata. The spectacular flower spike bears large, pendant, cream-white flowers, sometimes tinged with purple. The display, when it occurs, is striking — Plant Delights Nursery describes it as “spectacular 3-foot-tall flower spikes of large white bells.”
The fruit is the same fleshy, indehiscent, banana-shaped berry as in all Yucca baccata — the defining character of the species complex and of the subgenus Yucca. It is edible.
Distribution and habitat
Yucca arizonica is restricted to south-eastern Arizona and south-western New Mexico — a much narrower range than that of var. baccata, which spans seven US states and three Mexican states. It occurs in the transition zone between the Sonoran and Chihuahuan deserts, at elevations of approximately 900–1,800 m (3,000–6,000 feet).
The USDA Forest Service FEIS review describes the habitat as “moist regions at elevations ranging from 3,000 to 4,000 feet (914–1,219 m)” — relatively moist by desert standards, meaning that Yucca arizonica occurs in somewhat less extreme conditions than the most arid desert populations of var. baccata. It grows on undeveloped soils with mixed desert grasses and other desert shrubs.
This geographical restriction to Arizona and New Mexico, combined with the distinctive arborescent habit and filiferous leaf margins, is the primary basis on which various authors have argued for species or subspecies rank. The overlap with var. baccata in the same general region complicates the picture, however, and the FNA treats both as varieties of a single species.
Ethnobotany
The uses of Yucca arizonica overlap broadly with those documented for Yucca baccata as a whole (see the species page on Yucca baccata for a comprehensive treatment). The fleshy fruit was eaten raw, roasted or baked and dried for storage. The leaves provided fibre for cordage, baskets, mats and sandals. The roots were used as soap.
One ethnobotanical note specific to this entity: the Tohono O’odham (Papago) people of southern Arizona used the roots of var. brevifolia (= Yucca arizonica) specifically for red fibre in basket-making — a distinctive use that took advantage of the reddish pigment in the root material to produce coloured patterns woven into their baskets.
Cultivation
Climate suitability
Yucca arizonica shares the cold hardiness of the broader Yucca baccata complex: approximately –20 to –25 °C in dry, well-drained conditions. Its native elevation range (900–1,800 m) includes areas with regular hard frost and occasional snow. Plant Delights Nursery notes that plants from elevations up to 1,800 m (6,000 feet) “should have good cold hardiness if kept dry.” This makes Yucca arizonica one of the hardiest arborescent, fleshy-fruited yuccas available — considerably hardier than arborescent species like Yucca gigantea (–5 to –7 °C), Yucca valida (–3 to –5 °C) or Yucca aloifolia (–10 to –12 °C).
The critical advantage of Yucca arizonica for cold-climate gardeners is that it offers the tree-form yucca silhouette — the trunked, rosette-crowned architectural form that most people picture when they think of a desert yucca — with the cold tolerance of the banana yucca complex. Most tree-form yuccas of comparable hardiness (Yucca faxoniana, Yucca rostrata, Yucca elata) reach much greater ultimate height. Yucca arizonica stays relatively compact (to 2 m), making it suitable for smaller gardens where a 7 m yucca tree would be overwhelming.
Soil and drainage
Excellent drainage is essential, as with all Yucca baccata forms. The species grows on rocky slopes and undeveloped soils in its native habitat. A mineral-rich, fast-draining substrate — gravel, pumice, volcanic lapilli, decomposed granite — is ideal. It tolerates a broad pH range from mildly acid to mildly alkaline.
Light
Full sun is essential.
Watering
Extremely drought-tolerant once established. The “moist region” habitat description refers to the relatively higher precipitation of its native range compared with the most extreme desert lowlands — not to a requirement for supplementary irrigation. No watering is needed in any climate with meaningful rainfall.
Growth rate
Slow to moderate. The thick trunk develops gradually, but the overall growth rate is faster than for many acaulescent yuccas, reflecting the greater vigour of the caulescent growth form. The boat-shaped leaves and stocky trunk make the plant architecturally impressive even at a relatively young age.
Cold hardiness comparison
| Species | Approx. minimum temperature | Notes |
|---|---|---|
| Yucca arizonica (= Y. baccata var. brevifolia) | –20 to –25 °C | The hardiest arborescent fleshy-fruited yucca; compact (to 2 m); AZ/NM |
| Yucca × schottii | –15 to –20 °C | Stabilised hybrid; sky-island mountains; smooth leaf margins |
| Yucca faxoniana | –15 to –18 °C | Single trunk to 6 m; fine filaments; Trans-Pecos |
| Yucca rostrata | –15 to –18 °C | Blue rosette; single trunk; dry capsule |
| Yucca elata | –15 to –18 °C | Graceful; thin leaves; deep vertical rhizome |
| Yucca gigantea (= Y. elephantipes) | –5 to –7 °C | Tropical origin; spineless; much less hardy |
Landscape use
Yucca arizonica is an outstanding compact specimen yucca for desert gardens, xeriscapes, gravel gardens, Mediterranean-style landscapes and cold-climate gardens where an arborescent yucca silhouette is desired without the massive scale of species like Yucca filifera or Yucca faxoniana. The thick trunk, dense rosette of broad, boat-shaped, blue-green leaves and spectacular flower spikes make it a striking architectural focal point. It is effective as a solitary specimen, in a mixed planting with agaves, dasylirions, nolinas and cacti, or in a large container.
It is also an important plant for butterfly gardens in south-eastern Arizona: it is a host plant for the ursine giant skipper (Megathymus ursus) and the yucca giant-skipper (Megathymus yuccae), whose caterpillars bore into the roots and leaf bases.
The species is rare in the nursery trade but available from specialist suppliers, notably Plant Delights Nursery (sold as Yucca arizonica) and occasionally from seed through specialist succulent and yucca sources.
Propagation
Seed is the primary method. As with all Yucca baccata forms, pollination in the wild is performed by obligate yucca moths. In European gardens, hand pollination is required.
Division of offsets. Plants may produce basal offsets, particularly if the main trunk is damaged.
Stem cuttings from the trunk root readily, as with other arborescent yuccas.
Pests and diseases
No major problems. Root rot from waterlogging is the principal risk. The species is deer-resistant, rabbit-proof and resistant to honey fungus.
Conservation
Yucca arizonica (/ Yucca baccata var. brevifolia) has not been independently assessed by the IUCN. In Arizona, all Yucca baccata varieties — including var. brevifolia — are classified as Salvage Restricted and Harvest Restricted under Arizona native plant legislation, meaning that plants cannot be collected, harvested or destroyed on state or private land without a permit. This protection applies directly to Yucca arizonica populations.
The species is not considered threatened at present. It is locally common in parts of its restricted range in south-eastern Arizona and south-western New Mexico. However, its narrower distribution compared with var. baccata means that it is more vulnerable to localised threats from development, road construction and overgrazing.
Authority websites and online databases
Plants of the World Online (POWO) — Royal Botanic Gardens, Kew
Treated as a synonym of Yucca baccata var. brevifolia.
Yucca arizonica: https://powo.science.kew.org/taxon/…
Yucca baccata var. brevifolia: https://powo.science.kew.org/taxon/…
Flora of North America (FNA)
Treated under Yucca baccata var. brevifolia.
http://www.efloras.org/florataxon.aspx…
USDA Forest Service — Fire Effects Information System (FEIS)
Ecological treatment under Yucca baccata, including distribution and habitat data for var. brevifolia.
https://www.fs.usda.gov/database/feis/plants/shrub/yucbac/all.html
Llifle — Encyclopedia of Living Forms
Detailed species account with synonymy and morphological comparison.
https://www.llifle.net/Encyclopedia/SUCCULENTS/…
Plant Delights Nursery
Horticultural description and availability.
https://www.plantdelights.com/products/yucca-arizonica
iNaturalist
Citizen-science observations (often filed under Yucca baccata).
https://www.inaturalist.org/taxa/62640-Yucca-baccata
Bibliography
McKelvey, S.D. — “New species of Yucca.” Journal of the Arnold Arboretum 16: 268–270, 1935. Original descriptions of Yucca thornberi (p. 268) and Yucca arizonica (p. 270).
McKelvey, S.D. — Yuccas of the Southwestern United States, Part 1, 1938. Description of Yucca confinis (p. 49) and comprehensive treatment of the complex.
Benson, L.D. & Darrow, R.A. — “A manual of Southwestern desert trees and shrubs.” American Journal of Botany 30: 234, 1943. The combination Yucca baccata var. brevifolia, under which all the above names are now synonymised.
Trelease, W. — “The Yucceae.” Report (Annual) of the Missouri Botanical Garden 13: 27–133, 1902. Includes the illegitimate Yucca brevifolia Schott ex Trel. (not Engelmann 1871).
Hochstätter, F. — “Yucca baccata subsp. thornberi.” Succulenta 80: 172, 2001. Elevation to subspecific rank.
Hochstätter, F. (ed.) — Yucca (Agavaceae). Band 3: Mexico and Baja California. Self-published, 2004. ISBN 3-00-013124-8. Monographic treatment.
Hess, W.J. & Robbins, R.L. — Treatment of Yucca baccata var. brevifolia in Flora of North America, vol. 26. The current standard floristic treatment.
Groen, A.H. — 2005. Yucca baccata. USDA Forest Service, Fire Effects Information System (FEIS). Includes ecological data for var. brevifolia.
Torrey, J. — Botany of the Mexican Boundary [Report on the United States and Mexican Boundary Survey], 2(1): 221, 1859. Original description of Yucca baccata (the parent species).
Irish, M. & Irish, G. — Agaves, Yuccas, and Related Plants: A Gardener’s Guide. Timber Press, 2000. Practical cultivation advice.
Eggli, U. (ed.) — Illustrated Handbook of Succulent Plants: Monocotyledons. Springer, 2001. Comprehensive reference.