Yucca × schottii Engelm. — Schott’s yucca, mountain yucca, or hoary yucca — is the yucca of the sky islands. Native to the isolated mountain ranges of south-eastern Arizona, the boot-heel of south-western New Mexico and the northern fringes of Sonora and Chihuahua, it grows at higher elevations than any other tree-form yucca in its range, in the pine-oak woodlands and montane canyons where the Sierra Madre Occidental meets the Chihuahuan and Sonoran deserts. For over a century it was treated as a straightforward species, Yucca schottii. It is now recognised as something more remarkable: a stabilised natural hybrid — a nothospecies, indicated by the “×” in its name — that has established itself as a self-sustaining, freely reproducing entity in the wild. But the identity of its parents remains debated. POWO (Kew) gives the hybrid formula as Yucca baccata × Yucca madrensis. Some field guides cite Yucca baccata × Yucca elata. And the most careful treatment — by Lenz and Hanson (2000) — suggested an even more complex picture: a hybrid complex involving Yucca baccata, Yucca elata and Yucca madrensis. Whichever parentage proves correct, Yucca × schottii is a fascinating case study in plant hybridisation and speciation — and an outstanding cold-hardy garden yucca.
This page covers the taxonomy, hybrid origin, morphology, ecology, cultivation and conservation of Yucca × schottii, and can be read alongside the species pages on its putative parents (Yucca baccata, Yucca madrensis, Yucca elata), the hub page on the genus Yucca and the broader agavoids guide.
Taxonomy and the parentage debate
A species that became a hybrid
Yucca × schottii was originally described by George Engelmann as a species, Yucca schottii, named after Arthur Schott, a German-American naturalist who collected plants along the United States–Mexico boundary in the 1850s. For most of the twentieth century, the name was used without question for the common mountain yucca of the Arizona sky islands.
The re-evaluation began with the work of Lee W. Lenz and Mark A. Hanson (2000), published as “Typification and change in status of Yucca schottii (Agavaceae)” in Aliso 19: 93–98. Lenz and Hanson made two critical observations. First, they determined that the plants currently identified as Yucca schottii in the field — tall, blue-leaved, trunked yuccas — were not congruent with Engelmann’s original description. What most people were calling Yucca schottii was, in Lenz and Hanson’s view, more correctly referred to Yucca madrensis Gentry. Second, they suggested that the true Yucca schottii — as typified by Engelmann’s original material — represented not a species but a hybrid complex among Yucca baccata, Yucca elata and Yucca madrensis.
The Flora of North America editorial committee noted this hypothesis but expressed scepticism about the potential for crosses between baccate species (Yucca baccata, Yucca madrensis) and capsular species (Yucca elata), which belong to different subgenera (Yucca and Chaenocarpa respectively). Cross-subgeneric hybridisation — between a fleshy-fruited and a dry-fruited yucca — would be remarkable if confirmed.
Current nomenclatural status
POWO (Kew) now treats the plant as Yucca × schottii — a nothospecies — with the hybrid formula Yucca baccata × Yucca madrensis. This two-parent formula excludes Yucca elata from the parentage, effectively siding with the baccate-only hybridisation hypothesis. Several field guides and popular references instead cite Yucca baccata × Yucca elata, reflecting the pre-Lenz tradition and the morphological impression of a plant that combines the grey-green leaf colour of Yucca baccata with the tall, branched, trunked form of Yucca elata.
| Source | Proposed parentage | Notes |
|---|---|---|
| POWO (Kew) | Yucca baccata × Yucca madrensis | Current accepted formula; both parents are baccate (fleshy-fruited) |
| Lenz & Hanson (2000) | Hybrid complex: Yucca baccata × Yucca elata × Yucca madrensis | Three-parent hypothesis; involves cross between baccate and capsular subgenera |
| Various field guides; Dave’s Garden; americansouthwest.net | Yucca baccata × Yucca elata | Older, popular interpretation based on morphological impression |
| FNA editorial committee | Uncertain; sceptical of baccate × capsular crosses | Acknowledged the Lenz & Hanson hypothesis but did not endorse it |
The resolution of this debate will require further molecular phylogenetic work. For this article, we follow POWO in treating Yucca × schottii as Yucca baccata × Yucca madrensis, while noting the competing hypotheses.
Synonyms
POWO lists several synonyms: Sarcoyucca schottii (Engelm.) Linding. (1933), Yucca × brasiliensis Sprenger (1903), Yucca × macrocarpa Engelm. (1881) and Yucca × puberula Torr. (1859, nom. illeg.).
| Family | Asparagaceae |
| Subfamily | Agavoideae |
| Genus | Yucca L. |
| Nothospecies | Yucca × schottii Engelm. |
| Hybrid formula (POWO) | Yucca baccata × Yucca madrensis |
Common names: Schott’s Yucca, Mountain Yucca, Hoary Yucca.
Morphology
Yucca × schottii is a caulescent, arborescent yucca — intermediate in form between its two putative parents. It develops a stout trunk, typically branching a few times near the base (but usually not higher), reaching heights of up to 4.5 m (15 feet), though more commonly 1–3 m. The trunk is clothed with persistent dead leaves. Mature plants may have several stems, giving the plant a multi-headed but not densely branched silhouette — more open and sculptural than the heavily branched Yucca filifera or Yucca valida.
The leaves are among the most distinctive in the genus. They are up to 75 cm (30 inches) long and approximately 5 cm (2 inches) wide (widest in the middle), semi-flexible, flattish to concavo-convex toward the tips, and coloured grey-green to blue-green — the “hoary” (grey-frosted) appearance that gives the plant one of its common names. The margins are smooth and lack filaments — a key diagnostic character that instantly separates Yucca × schottii from Yucca schidigera (which has conspicuous curly filaments), Yucca baccata (coarse curling fibres) and Yucca elata (fine white filaments). The terminal spine is sharp. Young leaves are erect; older leaves become increasingly reflexed (bending downward), giving the rosette a layered, cascading appearance.
The inflorescence is an erect, showy panicle that partly emerges from and partly extends beyond the leaf rosette. The flowers are pendant, fleshy, egg-shaped, with six white to cream tepals that may be tinged with purple. Flowering occurs in summer, coinciding with the monsoon rains in the sky-island mountains. The flowers are pollinated by yucca moths.
The fruit is a large, fleshy, succulent, pendant, green berry — indehiscent (not splitting open at maturity). This baccate fruit character is inherited from the baccate parentage (Yucca baccata and/or Yucca madrensis) and confirms placement in the subgenus Yucca. The fruit is edible.
Distribution and habitat
Yucca × schottii is native to the Madrean sky islands — the isolated mountain ranges that rise like forested archipelagos from the desert seas of south-eastern Arizona and adjacent regions. Its range includes:
United States: south-eastern Arizona (Chiricahua Mountains, Santa Catalina Mountains, Huachuca Mountains, Santa Rita Mountains, Patagonia Mountains and other ranges) and the boot-heel region of extreme south-western New Mexico.
Mexico: northern Sonora and extreme north-western Chihuahua.
The species is called “mountain yucca” precisely because it grows at higher elevations than other tree-like yuccas in its range. While Yucca elata and Yucca baccata occupy the desert grassland and desert scrub at lower elevations, Yucca × schottii is found in the Madrean pine-oak woodland and montane canyons above them — typically at 1,200–2,100 m elevation. This is a transitional zone between the Sonoran/Chihuahuan desert lowlands and the cool montane forests, characterised by oaks (Quercus emoryi, Quercus arizonica, Quercus hypoleucoides), junipers (Juniperus deppeana), pines (Pinus cembroides, Pinus leiophylla) and a rich understory of agaves, dasylirions and other Madrean endemics.
The Madrean sky-island archipelago is one of the most biodiverse terrestrial ecosystems in North America. The isolated mountain ranges, surrounded by desert, function as ecological islands — each harbouring a distinctive assemblage of montane species with strong Mexican affinities, separated from one another by inhospitable lowland desert. Yucca × schottii is a characteristic element of this landscape and coexists with both of its putative parents: Yucca baccata occurs at lower elevations on the flanks of the same mountains, and Yucca madrensis occurs in similar or slightly higher montane habitats.
A successful hybrid
Yucca × schottii is not a sterile, first-generation hybrid doomed to disappear without continued crossing between its parents. It is a firmly established, self-sustaining entity that reproduces freely in the wild, both sexually (via yucca moth pollination, producing fertile seed) and vegetatively (through occasional basal offsets). It has its own stable morphological identity — recognisable in the field — and its own ecological niche (higher-elevation montane woodland, above the range of most lowland yuccas). In this sense, it behaves like a species, regardless of its hybrid origin.
This is not unique in the plant world — many widely accepted plant “species” are of hybrid origin — but it raises interesting questions about what it means to be a species versus a hybrid. Yucca × schottii illustrates that the distinction is not always clear-cut, and that hybridisation can generate new, ecologically viable, self-perpetuating lineages.
Yucca × schottii is also a host plant for the ursine giant skipper butterfly (Megathymus ursus), a rare and spectacular insect whose caterpillars bore into the roots and leaf bases of yuccas. This butterfly is restricted to the sky-island mountains of southern Arizona, southern New Mexico, western Texas and Nuevo León, and its dependence on Yucca × schottii and Yucca baccata gives both plants additional conservation significance.
Cultivation
Climate suitability
Yucca × schottii is an excellent cold-hardy yucca for temperate and Mediterranean gardens. Its montane origin at 1,200–2,100 m in the sky-island mountains — where winters are cold, with regular frost, occasional snow and temperatures well below freezing — gives it a hardiness estimated at –15 to –20 °C in dry, continental conditions. This places it among the hardiest arborescent yuccas available, comparable to Yucca faxoniana and Yucca rostrata, and considerably more cold-tolerant than lowland species like Yucca gigantea (= Yucca elephantipes) or Yucca aloifolia.
As with all montane desert yuccas, winter dryness is as important as absolute cold tolerance. A well-drained position is essential to prevent root rot during cold, wet winters.
Soil and drainage
Good drainage is important. The species grows on rocky mountain slopes with thin, mineral soils. In cultivation, a gritty, mineral-rich substrate with minimal organic matter is ideal. It tolerates a range of pH from mildly acid to mildly alkaline.
Light
Full sun to light shade. The species grows in open pine-oak woodland — more shade-tolerant than extreme desert yuccas, and an asset in gardens where full, searing sun is not available. It performs well against a south-facing wall or in a mixed border with other Madrean plants.
Watering
Drought-tolerant once established. Tolerates summer moisture better than extreme desert species, reflecting the monsoon rainfall pattern of the sky-island mountains. Winter dryness is preferred.
Growth rate and habit
Moderate. The plant develops its trunk relatively efficiently and can reach an impressive size within a decade or two in good conditions. The grey-green leaves, layered rosette and open branching habit give it an architectural elegance that works beautifully in both formal and naturalistic garden settings. The trunk is typically 1–3 m in garden conditions, occasionally reaching 4.5 m in old specimens.
Cold hardiness comparison
| Species | Approx. minimum temperature | Notes |
|---|---|---|
| Yucca baccata | –20 to –25 °C | Acaulescent; putative parent (fleshy fruit) |
| Yucca × schottii | –15 to –20 °C | Stabilised hybrid; sky-island mountains; arborescent; smooth leaf margins |
| Yucca madrensis | –12 to –18 °C (estimated) | Putative parent (fleshy fruit); compact; Sierra Madre Occidental |
| Yucca elata | –15 to –18 °C | Possible additional parent (dry capsule); deep rhizome; graceful habit |
| Yucca rostrata | –15 to –18 °C | Blue rosette; Chihuahuan Desert; dry capsule |
| Yucca faxoniana | –15 to –18 °C | Single trunk; Trans-Pecos; fine filaments |
Landscape use
Yucca × schottii is one of the finest yuccas for temperate and Mediterranean gardens. Its blue-grey foliage, open branching, layered rosettes and moderate size make it an outstanding specimen plant with genuine year-round architectural interest. It is less massive and more manageable than Yucca filifera or Yucca faxoniana, but more trunked and dramatic than acaulescent species like Yucca baccata or Yucca glauca. It associates naturally with Agave parryi, Agave havardiana, Dasylirion wheeleri, Nolina microcarpa and Chihuahuan/Madrean companion plants. In British and northern European gardens with good drainage, it is an excellent alternative to the popular but more frost-sensitive Yucca aloifolia.
The terminal spine is sharp and the plant should be sited away from high-traffic areas.
Propagation
Seed. Yucca × schottii produces fertile seed via yucca moth pollination in the wild. In European gardens, hand pollination is required. Seed germinates at moderate temperatures (15–21 °C).
Division of offsets. The plant occasionally produces basal offsets that can be separated and replanted.
Stem cuttings from the trunk may be attempted.
Pests and diseases
No major problems. Root rot from waterlogging is the primary risk. The species is resistant to honey fungus and immune to rabbit browsing.
In the wild, the ursine giant skipper (Megathymus ursus) larvae bore into the roots and leaf bases. This is a natural ecological relationship, not a pest problem in the strict sense, and the butterfly is itself a rare and protected insect.
Conservation
Yucca × schottii has not been formally assessed on the IUCN Red List. It is common in the sky-island mountains of south-eastern Arizona, where it occurs in pine-oak woodland that is largely protected within the Coronado National Forest, the Chiricahua National Monument, the Huachuca Mountains military reservation and other federal and state lands. In Mexico, the habitat is less well protected but extensive in remote mountain areas.
Climate change is a long-term concern for sky-island species: rising temperatures and altered precipitation patterns may shift the montane habitats upward, compressing the available space for species like Yucca × schottii that depend on the mid-elevation pine-oak zone. However, the plant’s hybrid vigour and its capacity to reproduce both sexually and vegetatively may provide resilience against moderate environmental change.
The conservation of Yucca × schottii is indirectly dependent on the conservation of its parent species — particularly Yucca madrensis, which is rare, geographically isolated and restricted to the Sierra Madre Occidental. The loss of Yucca madrensis would eliminate one half of the genetic heritage of Yucca × schottii and prevent the ongoing generation of new hybrid individuals.
Authority websites and online databases
Plants of the World Online (POWO) — Royal Botanic Gardens, Kew
Nothospecies page, including hybrid formula and synonyms.
https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:325011-2
iNaturalist
Citizen-science observations across the sky-island range.
https://www.inaturalist.org/taxa/56022-Yucca-schottii
American Southwest — Plant Guide
Field identification account with habitat photographs.
https://www.americansouthwest.net/plants/…
Trees of Stanford & Environs
Detailed treatment including the FNA commentary on the Lenz & Hanson reclassification.
https://trees.stanford.edu/ENCYC/YUCschot.htm
Bibliography
Engelmann, G. — Original description of Yucca schottii. Named after Arthur Schott (1814–1875), naturalist on the United States–Mexico Boundary Survey.
Lenz, L.W. & Hanson, M.A. — “Typification and change in status of Yucca schottii (Agavaceae).” Aliso 19: 93–98, 2000. The key paper: demonstrated that field-identified Y. schottii was not congruent with Engelmann’s type, suggested reassignment of those plants to Y. madrensis, and proposed that the true Y. schottii is a hybrid complex involving Y. baccata, Y. elata and Y. madrensis.
Gentry, H.S. — The Agave Family in Sonora. USDA Agriculture Handbook 399, 1972. Includes the description of Yucca madrensis, one of the putative parents.
Pellmyr, O. et al. — “The phylogeny of yuccas.” Molecular Phylogenetics and Evolution 43: 493–501, 2007. Molecular phylogeny relevant to the relationships of the parent species.
Trelease, W. — “The Yucceae.” Report (Annual) of the Missouri Botanical Garden 13: 27–133, 1902. Foundational genus revision.
McKelvey, S.D. — Yuccas of the Southwestern United States, Parts 1–2. Jamaica Plain: Arnold Arboretum of Harvard University, 1938–1947. Comprehensive monograph.
Hess, W.J. & Robbins, R.L. — Treatment of Yucca in Flora of North America, vol. 26. Standard modern floristic account.
Hochstätter, F. (ed.) — Yucca (Agavaceae). Band 3: Mexico and Baja California. Self-published, 2004. ISBN 3-00-013124-8.
Irish, M. & Irish, G. — Agaves, Yuccas, and Related Plants: A Gardener’s Guide. Timber Press, 2000. Practical cultivation advice; detailed field description of Y. × schottii.
Albano, P.-O. — La Connaissance des Plantes Exotiques. Édisud, Aix-en-Provence, 2003. European cultivation context.
Allred, K.W. — Flora Neomexicana, 2nd edition, vol. 1. Range Science Herbarium, Las Cruces, New Mexico, 2012. New Mexican records.