Xanthocyparis description

Xanthocyparis

Farjon & T.H.Nguyèn (2002)

Common names

None have been recorded, but "yellow cypress" is a transliteration of the scientific name.

Taxonomic notes

A genus of two species:

X. guangxiensis Yu L.Jiang, Y.S.Huang, Jia L.Li & K.S.Mao
X. vietnamensis Farjon & T.H.Nguyèn

Xanthocyparis was described in 2002 based on a new conifer that had recently been discovered in northern Viet Nam (Farjon et al. 2002). The new plant was assigned to Xanthocyparis, with X. vietnamensis as the type species; the genus remained monotypic until late 2024, when a second species, X. guangxiensis, was described from Guangxi in China. Among other things, the two species are distinguished by ploidy: X. guangxiensis, like almost all conifers, is diploid. X. vietnamensis is tetraploid (Jiang et al 2024).

Based on many molecular analyses supplemented by morphological and other lines of evidence (see Cupressus for discussion), the prevalent view now is that Xanthocyparis is sister to the New World cypresses, Callitropsis and Hesperocyparis, in a clade sister to Cupressus and Juniperus (Yang et al. 2022). Why is this southeast Asian genus sister to 18 other species that are now endemic to North and Central America? A molecular clock analysis (Terry et al. 2016) suggests that the division between Xanthocyparis and the other New World cypresses occurred in the Eocene (45 million years ago), when warm and humid climates existed at high latitudes and there was an extensive Beringian land connection between North America and Asia (see Terry et al. 2016 for detailed discussion of why movement across Beringia is a likely scenario). It is likely that precursors to the modern Xanthocyparis were present in northern regions of both North America and Asia during the Eocene. The New World cypresses migrated southwards during later (Oligocene to modern) climatic cooling, and their Asian relatives, of which Xanthocyparis is now the sole survivor, would have done likewise. The gene duplication that gave rise to the tetraploid X. vietnamensis is likely a relatively recent event.

Description

Monoecious evergreen trees with fibrous bark exfoliating in longitudinal strips and yellowish, slow-growing heartwood. Foliage branches spreading in plagiotropic sprays or drooping, forming a pyramidal, conical or irregular flat-topped crown. Leaves resinous. Foliage of three types: juvenile needle-like leaves, transitional leaves, and adult scale-like leaves. Juvenile leaves are present on seedlings and continue to occur on plants of all ages (juvenile to mature), radially disposed in alternating whorls of four; twigs with this type of leaves are always sterile. Transitional leaves are also present on plants of all ages, decussate, divided into facials and laterals of nearly equal size; laterals are weakly disposed in a plane. Foliage branchlets with transitional leaves are usually sterile. Adult leaves are present only on mature trees, decussate, dimorphic in shape and size with laterals strongly flattened and disposed in a plane; foliage branchlets are often fertile. Pollen cones small, terminal and solitary on lateral branchlets with small scale leaves; microsporophylls 10-16, decussate, peltate, bearing 2 or 3 relatively large pollen sacs. Seed cones terminal and solitary on lateral branchlets with unmodified scale leaves, opening wide. Bract-scale complexes 4 or 6 in decussate pairs fused at base with connate upper pairs, spreading wide to release the seeds, valvate to subpeltate, with a prominent central umbo. Central columella present or absent, small. Ovules axillary to bracts, 1 to 5 per bract; seeds usually fewer, concentrated on upper pair (if 2 pairs) or middle pair (if 3 pairs) of scales, flattened, with two thin lateral wings. Seedlings with 2 cotyledons (Farjon 2010).

Jiang et al. (2024) provide this key to the species:

Mature cone with diameter <1 cm; mature seed about 4.3 mg dry weight; resin canals in the cortex of the adaxial region of young branch junctions (about 3–15 mm diameter) not well developed; the branch junctions do not swell, or gradually swell, with at most a light resinous scent after sectioning. (2n = 2x).	X. guangxiensis
Mature cone with diameter <1 cm; mature seed about 15.7 mg dry weight; resin canals in the cortex of the adaxial region of young branch junctions (about 3–15 mm in diameter) are developed; the branch junctions swell and bulge out, rich in resin, with a strong resinous scent after sectioning. (2n = 4x).	X. vietnamensis

Distribution and Ecology

Occurs in China: Guangxi and Viet Nam, at elevations of 700-1400 m in primary forest on carbonate karst mountain ridges. Populations are small and highly localized (Jiang et al. 2024). See the species accounts for further detail.

Remarkable Specimens

No data as of 2026-04-03.

Ethnobotany

See the species accounts.

Observations

See the species accounts.

Remarks

The genus name is from the Greek for "yellow cypress", referring to the color of the wood (Farjon et al. 2002).

Citations

Farjon, A., Nguyen Tien Hiep, D. K. Harder, Phan Ke Loc, and L. Averyanov. 2002. A new genus and species in Cupressaceae (Coniferales) from Northern Vietnam, Xanthocyparis vietnamensis. Novon 12:179-189.

Jiang, Yu‐Liang, Jia‐Liang Li, Richard Ian Milne, Khang Sinh Nguyen, Zhi‐Tong Han, Yu‐Song Huang, Wei‐Bin Xu, Yan Liu, and Kang‐Shan Mao. 2024. Biogeographic, climatic, morphological, cytological and molecular data reveal a new diploid species from China in the genus Xanthocyparis (Cupressaceae)." Taxon 73(5):1170-1186. https://doi.org/10.1002/tax.13246.

Terry, Randall G., Matthew I. Pyne, Jim A. Bartel, and Robert P. Adams. 2016. A molecular biogeography of the New World cypresses (Callitropsis, Hesperocyparis; Cupressaceae). Plant Systematics and Evolution 302:921–942. https://doi.org/10.1007/s00606-016-1308-4.

Yang, Yong, David Kay Ferguson, Bing Liu, Kang-Shan Mao, Lian-Ming Gao, Shou-Zhou Zhang, Tao Wan, Keith Rushforth, and Zhi-Xiang Zhang. 2022. Recent advances on phylogenomics of gymnosperms and a new classification. Plant Diversity 44(4):340-350.