Cupressus tonkinensis
Hoàng dàn [Vietnamese] (FIPI 1996).
Type: Viet Nam, Lang San province, Huu Lüng district, Cai Kinh Commune ["Kai Kinsh, Lausoy"], 21.55°N, 106.40°E, Dec. 1913, Eberhardt 5073 (holotype, NY). Syn. Cupressus funebris subsp. tonkinensis Silba (2005).
Even up to now (2024), most authors have synonymized this species under C. torulosa; if that were true, it would be the most spectacular range disjunction of any conifer (several thousand kilometers). Even Silba (1994) missed the most fundamental difference between the two species: C. tonkinensis has dimorphic foliage, but C. torulosa does not. Accurate circumscription of the species finally arrived with a comprehensive study by Little et al. (2011). C. tonkinensis seemingly shares a southeast Asian clade with C. chengiana and C. funebris (Little et al. 2011, Terry et al. 2018), but there is not currently (2024) very much confidence about phylogenetics within Cupressus.
Monoecious evergreen trees to 10+ m tall and 40+ cm dbh, typically with a single trunk. Outer bark on the main trunk gray-brown, exfoliating in linear strips. Antepenultimate twigs arranged in one plane or two planes. Penultimate twigs arranged in one plane, 4-22% of the nodes bearing branches; twigs strictly one per node, 1-1.3 mm diameter, 12-31 mm long. Leaves externally dimorphic. Juvenile (needle-like) leaves appear only on young individuals; they are externally dimorphic, glossy green. Ultimate twigs are 0.8-1.1 mm diameter, 4.3-9.5) mm long. Facial leaves on ultimate twigs 0.7-1 mm long, with 50-94% bearing resin glands with slot-like external faces, rarely with resinous exudates; leaf apex acute. Lateral leaves on ultimate twigs 0.8-1.1 mm long, with 0-80% of the leaves bearing resin glands with slot-like external faces, rarely with resinous exudates; leaf apex acute. Pollen cones oblong, with 6 pairs of decussate cone scales. Seed cones globose, 7-9 × 8-10 mm, comprised of 6-8 cone scales; mucro on the boss of apical cone scales entire or ciliate; peduncle leaves externally monomorphic; cones non-serotinous, the scales opening and dying upon seed maturation. Seeds irregular in shape, 3-3.7 mm long, 1.8-3.5 mm wide, 0.7-1.4 mm thick; seed coat not glaucous, dull red-brown; seed wings well-developed; 2 years required for seed maturation. Hilum 0.6-1.1 mm, 0.3-0.5 mm wide (Little et al. 2011).
The species closely resembles Cupressus torulosa, from which it differs mainly in having dimorphic leaves; also, C. torulosa is a species of the western Himalaya. It also closely resembles C. funebris, which has a mucronate tip on the apex of the ultimate segment lateral leaves (photos in Little et al. [2011] illustrate the difference).
Viet Nam, Lang Son province, the Cai Kinh limestone massif in Hüu Lüng and Chi Läng districts. As such it is a narrow endemic. The only known mature tree in habitat is located within the Hüu Liên Reserve; collections cited by Silba (1994, 2005) from Guizhou (China) have been identified as Cupressus funebris. Apart from this, about 20 trees exist in a small plantation established at the edge of the Huu Liên Reserve in the 1990s, and several cultivated trees are known from the surrounding villages (Little et al. 2011). The species is restricted to ridges and upper slopes of karst limestone formations, at 350-650 m elevation. See Little et al. (2011) for detailed discussion of climate variables and associated vegetation. These karst ridges support as many as 10 species of conifers, which makes them one of the most unique, diverse, and endangered conifer habitats on Earth. Examples in the vicinity of the known C. tonkinensis habitat include Nageia fleuryi, Podocarpus neriifolius, and Pseudotsuga sinensis.
C. tonkinensis was recognized as endangered in 1996, with a need for protection in its remaining natural distribution area in Lang Son and Tuyen Quang provinces, and plantations were called for to preserve the gene resource for further development of the species (FIPI 1996). It was listed as threatened/endangered in Vietnam by the WCMC (2001), the forerunner of the IUCN. Although the IUCN does not now recognize this species (conflating it with C. torulosa), Little et al. (2011) assessed it under IUCN methodology (probably V.3.1, but the authors do not specify) and determined it to be Critically Endangered based on a population reduction of more than 80% within the last three generations and a population size of less than 50 mature individuals, with an extent of occurrence of 204 km2 and an area of occupancy of less than 8 km2, all within one area.
Since only a single mature tree is known to exist in habitat, that is definitely a remarkable specimen.
In Viet Nam, Cupressus has always been valued for its fine timber and resin, and so it has always been heavily exploited. Since 1997, no commercial quantities of Cupressus have been available. Harvest restrictions were introduced as early as 1958, but little was done to stop the exploitation. By 2006, all exploitation or use of Cupressus "torulosa" was prohibited under Vietnamese law, and it was listed in Viet Nam's Red Data Book as Critically Endangered (Little et al. 2011).
See Little et al. (2011) for locations in Viet Nam where cultivated specimens can be found.
The epithet refers to Tonkin, a Romanization of Đông Kinh, which is an old name for northern Viet Nam.
Silba, John. 1994. J. Int. Conifer Preserv. Soc. 1:23.
Silba, John. 2005. J. Int. Conifer Preserv. Soc. 12:67.
[WCMC] World Conservation Monitoring Centre. The Socialist Republic of Viet Nam Appendix 5 - Threatened Plant Species. http://www.wcmc.org.uk/infoserv/countryp/vietnam/app5.html, accessed 2001.11.25, now defunct.
The species account at Threatened Conifers of the World (accessed 2024.12.12).
Last Modified 2024-12-14
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