Hesperocyparis macnabiana (A.Murray bis) Bartel — McNab western-cypress

Introduction

The McNab western-cypress, Hesperocyparis macnabiana, is an evergreen tree or large shrub occurring in scattered groves across California’s inner North Coast Ranges, Sierra Nevada foothills, and adjacent interior ranges. It belongs to the Macrocarpa Clade and is one of the easier western-cypresses to recognize in the field: mature foliage commonly bears conspicuous pit-like resin glands capable of producing visible droplets, the branchlets are slender and comb-like, and the globose cones have three to four pairs of scales with prominent conical umbos.

The species often grows in chaparral, foothill woodland, and open sites on serpentine-derived substrates. Genome-scale sampling places it close to H. nevadensis within the Macrocarpa radiation, clarifying why the latter was historically treated at times as a variety of H. macnabiana (Li et al. 2026). McNab western-cypress also forms natural hybrids with H. sargentii where the two meet; combined morphological and DNA evidence confirms that the intermediates are genuine hybrids rather than merely variable individuals (Little 2004).

Horticultural and Agricultural Uses

McNab western-cypress is grown mostly in conifer collections, native-plant landscapes, and dry-site plantings rather than as a major commercial cypress. Its compact, often broad-crowned habit, aromatic foliage, and tolerance of rocky or serpentine-influenced soils can be useful in sites that mimic its native dry-summer ecology. The active foliar resin glands are diagnostically valuable but can also make the foliage feel resinous when handled.

For horticultural and conservation collections, the natural hybrid zone with H. sargentii is a reason to maintain good accession records. Seed collected from mixed populations can contain hybrid ancestry; that is biologically interesting but should not be mistaken for pure-source conservation material when the goal is to preserve parental populations.

Conservation Concerns

The species is currently treated as Least Concern in the IUCN information incorporated by Plants of the World Online, reflecting its comparatively broad Californian range. That status does not mean individual groves are secure. Many populations remain small, isolated, and tied to fire-prone landscapes, with local threats from altered fire regimes, land use, and habitat disturbance (Royal Botanic Gardens, Kew 2026).

Like several Californian western-cypresses, H. macnabiana is an obligate seeder with persistent serotinous cones. Severe fire commonly kills mature trees but rapidly opens cones and creates establishment sites. Experimental heating shows that cones can respond strongly to wildfire-like temperatures while viable seed survives brief exposure (Milich et al. 2012). The conservation problem is therefore one of fire timing: repeated burning before reproductive maturity can erase a cohort, while complete fire exclusion can reduce opportunities for regeneration.

Additional Information

Plants of the World Online — Hesperocyparis macnabiana (opens in a new tab): Current Kew taxonomic, distributional, and conservation treatment.
Trees and Shrubs Online — Hesperocyparis macnabiana (opens in a new tab): Horticultural and descriptive account.
USDA Forest Service Fire Effects Information System — Hesperocyparis macnabiana (opens in a new tab): Literature synthesis on habitat and fire ecology.
Little 2004 — documented hybridization with H. sargentii (opens in a new tab): Morphological and molecular confirmation of natural hybridization.

References and Further Reading

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).

Little DP (2004) Documentation of hybridization between Californian cypresses: Cupressus macnabiana × sargentii. Systematic Botany 29(4): 825–833. https://doi.org/10.1600/0363644042451026 (opens in a new tab).

Milich KL, Stuart JD, Varner JM III, Merriam KE (2012) Seed viability and fire-related temperature treatments in serotinous California native Hesperocyparis species. Fire Ecology 8(2): 107–124. https://doi.org/10.4996/fireecology.0802107 (opens in a new tab).

Royal Botanic Gardens, Kew (2026) Hesperocyparis macnabiana (A.Murray bis) Bartel. Plants of the World Online. https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A60451555-2 (opens in a new tab).