Hesperocyparis arizonica (Greene) Bartel — Arizona western-cypress

Introduction

The Arizona western-cypress, Hesperocyparis arizonica, is an evergreen tree of mountain systems from central and southeastern Arizona through southwestern New Mexico and western Texas into northern Mexico. Tree TSAR uses a narrower species concept than many twentieth-century treatments, excluding lineages now recognized as H. glabra, H. nevadensis, H. montana, H. stephensonii, and H. revealiana. In this sense, H. arizonica belongs to the Arizonica Clade and occupies a range of pinyon-juniper, oak, canyon, and montane woodland settings.

True H. arizonica generally develops persistent fibrous or shreddy bark rather than the smooth exfoliating reddish bark characteristic of H. glabra. Morphology overlaps, however, and chemistry and molecular evidence add important independent support to the boundary (Bartel et al. 2003; Adams et al. 2010). Li et al. (2026) sampled one H. arizonica accession; its position within the Arizonica radiation supports the narrower lineage concept but should not be used to overstate range-wide genomic sampling.

Horticultural and Agricultural Uses

Arizona western-cypress is an established ornamental and environmental tree for dry climates. It is valued for evergreen foliage, drought tolerance after establishment, wind resistance, screening, and shelter, and has been planted beyond its native range. Plants perform best in full sun and well-drained soils, and the species’ mountain origin gives it a useful combination of drought adaptation and greater cold tolerance than some subtropical cypresses (Trees and Shrubs Online 2026; Royal Botanic Gardens, Kew 2026).

The horticultural name “Arizona cypress” has also been applied broadly to plants now assigned to H. glabra and to glaucous selections of uncertain provenance. For Tree TSAR purposes, cultivar names and ornamental color forms should not be used to blur the biological distinction between the two accepted species.

Conservation Concerns

The species is assessed as Least Concern in the IUCN information incorporated by Plants of the World Online, reflecting a comparatively broad distribution. Local populations can nevertheless be affected by severe drought, altered fire regimes, grazing, development, and the loss of mature seed-bearing trees, especially near the margins of the range (Royal Botanic Gardens, Kew 2026).

Fire response varies across the broad Arizona-cypress complex historically recognized by foresters, so management should use the narrower taxonomic identity and local population ecology rather than applying a single prescription to all former varieties. Provenance-aware conservation is particularly important because historical broad concepts can obscure which lineage is actually being protected or planted.

Additional Information

Plants of the World Online — Hesperocyparis arizonica (opens in a new tab): Current Kew nomenclatural, distributional, use, and conservation information.
Trees and Shrubs Online — Hesperocyparis arizonica (opens in a new tab): Horticultural and historical account.
USDA Forest Service Fire Effects Information System — Hesperocyparis arizonica (opens in a new tab): Literature synthesis on ecology and fire relationships.
Adams et al. 2010 — H. arizonica and H. glabra (opens in a new tab): Essential-oil evidence relevant to the modern species boundary.

References and Further Reading

Adams RP, Bartel JA, Thornburg DC, Allgood A (2010) Geographic variation in the leaf essential oils of Hesperocyparis arizonica and H. glabra. Phytologia 92(3): 366–387. https://www.biodiversitylibrary.org/part/220432 (opens in a new tab).

Bartel JA, Adams RP, James SA, Mumba LE, Pandey RN (2003) Variation among Cupressus species from the western hemisphere based on random amplified polymorphic DNAs. Biochemical Systematics and Ecology 31(7): 693–702. https://doi.org/10.1016/S0305-1978(02)00229-6 (opens in a new tab).

Li J, Jia S, Wu D, Tao W, Ruhsam M, Mao K (2026) Phylogenomics reveals the reticulate evolution and biogeographic history of New World cypresses, Hesperocyparis (Cupressaceae). Cladistics 42(2): 109–127. https://doi.org/10.1111/cla.70021 (opens in a new tab).

Royal Botanic Gardens, Kew (2026) Hesperocyparis arizonica (Greene) Bartel. Plants of the World Online. https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A60451546-2 (opens in a new tab).

Trees and Shrubs Online (2026) Hesperocyparis arizonica. https://www.treesandshrubsonline.org/articles/hesperocyparis/hesperocyparis-arizonica/ (opens in a new tab).