Hesperocyparis guadalupensis (S.Watson) Bartel — Guadelupe Island western-cypress

Introduction

The Guadelupe Island western-cypress, Hesperocyparis guadalupensis, is an evergreen tree endemic to Guadalupe Island off the Pacific coast of Baja California. Mature trees can become substantially larger than many mainland western-cypresses, with low-forking trunks, irregular crowns, bright-green scale foliage, and relatively large cones. The island lineage belongs to the Macrocarpa Clade, despite its long history of taxonomic association with the superficially similar Tecate western-cypress, H. forbesii (Li et al. 2026).

That historical association is understandable but evolutionarily misleading. H. guadalupensis and H. forbesii differ in chemistry, population structure, reproductive ecology, and genome-scale placement. The island species can release seed from mature cones much more readily without fire, whereas H. forbesii is tightly coupled to fire-driven cone opening. Li et al. (2026) sampled three Guadalupe Island accessions and associated them with the geographically remote H. stephensonii in the Macrocarpa radiation, while H. forbesii falls in the Arizonica Clade.

Horticultural and Agricultural Uses

Guadelupe Island western-cypress is principally a tree for specialist conifer collections, dry-climate botanical gardens, and conservation programs. Its relatively large size and bright foliage make it horticulturally attractive, but conservation provenance is more important than ornamental selection because the entire natural species comes from one oceanic island.

The species’ cone biology has practical implications for propagation. Mature cones can open after branch or tree death without the intense heating required by more strongly serotinous mainland species, so seed collection and storage do not require simulating wildfire to the same degree. That difference reflects the island’s historically less fire-driven ecology rather than a complete loss of serotiny (Garcillán 2010).

Conservation Concerns

Plants of the World Online incorporates an IUCN Endangered assessment for H. guadalupensis. The species suffered a severe demographic bottleneck when introduced goats suppressed seedling recruitment and degraded the island’s vegetation. Goat eradication produced a rapid and highly visible conservation response: new cohorts of cypress seedlings established around surviving stands, demonstrating that reproductive capacity had persisted even after a long period of browsing pressure (Garcillán et al. 2009).

Genetic evidence adds nuance to the conservation picture. Plastid studies found substantial haplotype diversity despite the island restriction, so conservation should protect the surviving population as a genetically structured lineage rather than assuming that a few cultivated trees adequately represent it (Rosas-Escobar et al. 2011). Continued recovery depends on maintaining the post-eradication vegetation trajectory, limiting new invasive-herbivore pressure, and monitoring fire, drought, and climate stress on a species whose entire wild distribution remains concentrated on one island.

Additional Information

Plants of the World Online — Hesperocyparis guadalupensis (opens in a new tab): Current Kew nomenclatural, distributional, and conservation treatment.
Trees and Shrubs Online — Hesperocyparis guadalupensis (opens in a new tab): Horticultural and historical account.
Rosas-Escobar et al. 2011 — plastid diversity (opens in a new tab): Population-genetic comparison of Guadalupe and Tecate western-cypresses.
Seventh California Islands Symposium — recruitment after goat eradication (opens in a new tab): Proceedings containing the demographic study of post-eradication recruitment.

References and Further Reading

Garcillán PP (2010) Seed release without fire in Callitropsis guadalupensis, a serotinous cypress of a Mediterranean-climate oceanic island. Journal of Arid Environments 74(4): 512–515. https://doi.org/10.1016/j.jaridenv.2009.09.017 (opens in a new tab).

Garcillán PP, Vega E, López-Reyes E (2009) Recruitment response of Guadalupe cypress (Callitropsis guadalupensis) three years after goat eradication on Guadalupe Island. In: Damiani CC, Garcelon DK (eds), Proceedings of the Seventh California Islands Symposium. Institute for Wildlife Studies, Arcata, California, pp 177–183.

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).

Rosas-Escobar P, Gernandt DS, Piñero D, Garcillán PP (2011) Plastid DNA diversity is higher in the island endemic Guadalupe cypress than in the continental Tecate cypress. PLOS ONE 6(1): e16133. https://doi.org/10.1371/journal.pone.0016133 (opens in a new tab).

Royal Botanic Gardens, Kew (2026) Hesperocyparis guadalupensis (S.Watson) Bartel. Plants of the World Online. https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A60451553-2 (opens in a new tab).