The Cupressaceae is now considered by some authorities to include the Taxodiaceae  whilst other treatments  maintain the two families as separate phylogenetic lines. My personal opinion is to consider the Cupressaceae in the traditional sense but to question whether Hayata's treatment (1932) of the Taxodiaceae as several distinct lineages may not be the most coherent approach - the main difference between Quinn's treatment in G adek et al. (2000) and Hayata's treatment is in the level of the units - Hayata has separate families, Quinn has subfamilies of Cupressaceae sensu lato. This paper concerns only the members of the Cupressaceae sensu stricto - Cupressoideae Richard ex Sweet (Hortus Britannica: 372, 1826).
Four members of the Cupressoideae are found in indigenous natural forest in Vietnam. These have been treated as belonging to the genera Calocedrus, Cupressus, Fokienia and Xanthocyparis. Some others are cultivated, such as Cupressus arizonica Greene at Dalat and Platycladus orientalis (L.f.) Franco at Hanoi.
1. Cupressus in Langson province
In 1919 Philippe Eberhardt collected material from a tree 8-10 m in height growing at Kaikinh in Langson province, Vietnam; the collection was numbered 5073 and his specimens are lodged at Paris (P) and New York (NY). Chevalier (1919) identified it as Cupressus funebris Endl. Silba (1994, 1998) described this material as a new species, Cupressus tonkinensis. He designated the NY specimen as the holotype and the P specimen as the isotype. Other authorities (e.g. Farjon 1998, p 45) have considered Cupressus tonkinensis to be a synonym of Cupressus torulosa D. Don, a species otherwise known only from the western Himalaya from central Nepal to northwest India and adjacent southwestern Tibet (Xizang). Luu & Thomas (2004), however, considered it to be a synonym of Cupressus funebris, though they expressed one or two reservations; they concluded that it was definitely not a synonym of Cupressus torulosa. Through the courtesy of the Curator of the Herbarium at the Royal Botanic Garden Edinburgh (E), I have been able to borrow the Paris isotype and see a photograph of the NY specimen. I have compared the Paris isotype with all the material of Cupressus torulosa in the Edinburgh herbarium. My observations relate specifically to the Paris isotype, although the photograph of the NY holotype appears to be the same. Both specimens are very fragile and fragmented.
The Paris isotype contains both foliage and one-year cones (the photograph of the holotype shows only foliage).
The cones are almost round and have 8 scales (4 pairs of decussate scales), each scale with a small prickle-like umbo.
The foliage on the most recent growths contains some shoots which are terete (round as in a cylinder); on these shoots the decussate pairs of leaves are indistinguishable. However, most foliage is in flattened shoots with dimorphic leaves; on these shoots the facial (Facial leaves are those facing you when a spray is laid flat) leaves have an obvious dorsal gland and are rhombic in shape; the laterals (Lateral leaves are those at the side when a spray is laid flat) are adpressed with a blunt rounded tip of 0.5 mm with only a weakly defined gland.
I examined the following material of Cupressus torulosa in the Edinburgh herbarium: Page 10715. Mussoorie Hill Station, India; Walter Koelz 20354. United Provinces, India; R. E. Cooper 5793. Jheri Kulu, Punjab, India; Stewart s.n. North West India; A. Anderson s.n.. Mussoorie, India; Stainton 7593. Mazana Kulu, Himachal Pradesh, India; Blinkworth (Hb. Wallich 6046B), Kumaon, North West India; G. Watt s.n. Thula, India; Hooker & Thomson, s.n.. Simla, India; Noshiro et al. 9455337 and 9455353. Dhawalagiri, Mustang, Central Nepal; Minaki et al. 9106095. Karnali, Dolpa, West Nepal; Stainton, Sykes & Williams 3273. Maikot, Nepal; Stainton, Sykes & Williams 1673. Tajlung, South of Tukucha, Kali Gandaki, Central Nepal; Stainton, Sykes & Williams 726. Larjung, South of Tukucha, Kali Gandaki, Central Nepal; J. R. Reid s.n. Nainital (India: Uttaranchal); F. M. Bailey s.n. Chaha, West Nepal.
This material of Cupressus torulosa differs from the Paris specimen of Eberhardt 5073 in the following characters: The cones (when present) have 10, occasionally 12 scales (i.e. 5, occasionally 6, pairs of scales); the scales in the one year cones (when present) have an umbo which is a prominent prickle making these cones spiky, not rounded; however in mature (two year old) and older cones the umbo becomes eroded, making the cones rounded in outline. The ultimate shoots are radially symmetrical with no differentiation into facial and lateral leaves and the sprays are three-dimentional, never in two-dimentional or flattened sprays. The foliage on the material of Cupressus torulosa is either smooth rounded (terete) or coarse rope-like with rough regular projections; the coarse rope-like foliage appears to be correlated with the drier inner-valley habitats and the terete foliage with the moister outer ranges.
The above considerations shows that Cupressus tonkinensis is clearly not referable to Cupressus torulosa, differing in the cones with only 8 (cf. 10-12) scales and in the mainly flattened foliage (cf. rounded) with distinct facial and lateral leaves. Taken with the geographical separation - from Laos to Sikkim! - Cupressus tonkinensis warrants specific status and is not a synonym of Cupressus torulosa.
Cupressus tonkinensis can be distinguished from Cupressus funebris - on the basis of the limited material available - by the foliage of C. tonkinensis being in flattened and sparse fan-shaped sprays and not in the long pendulous sprays which characterise Cupressus funebris. Also, the lateral leaves on the Paris isotype have blunt, adpressed tips, not the acute translucent tips to the lateral leaves of Cupressus funebris, and the glands on the facial leaves are more pronounced than in typical Cupressus funebris. The number of cone scales in Cupressus funebris ranges from 6-10, thus straddling the range of Cupressus tonkinensis.
Silba has cited two specimens at the Arnold Arboretum from Guizhou, China as belonging to Cupressus tonkinensis, viz. Y. Tsiang 8004 and Steward, Chiao & Cheo 10. Through the good offices of the two Curators, I have borrowed these and examined them at Edinburgh; they both fall within the range of Cupressus funebris and are not close to Cupressus tonkinensis. Cupressus tonkinensis is, on our current knowledge, a Vietnamese endemic.
At Huulung in Langson province [21°40'42"N, 106°22'42"E] at 220 m there is a grove of circa twenty trees. These were planted in the late 1980's; the seed is reported to have been collected from a tree or trees growing on the nearby karst limestone peaks; other trees are also cultivated in gardens in the vicinity. These trees are not fully mature but the adult foliage has the flattened sparse sprays of Cupressus tonkinensis. However, the tips of most of the lateral leaves are acute with a short incurved mucro; some leaves, however, have the blunt incurved tips characteristic of Cupressus tonkinensis.
My opinion is that the foliage of these trees, which are only about 15 years old, is in an intermediate stage between fully juvenile foliage (where the leaves are in whorls of four with the two decussate pairs superimposed) and fully adult. I consider (on the currently available information) that the Huulung trees are Cupressus tonkinensis.
Interestingly the Huulung trees have both adult (semi-adult?) and juvenile foliage on the same branches. Retained juvenile foliage seems to be a feature of Eastern Asian Cupressaceae. It is common for a decade or more on plants of Cupressus funebris and Cupressus chengiana S. Y. Hu and the genus Retinospora Sieb. & Zucc. was named for juvenile forms of Japanese Chamaecyparis. However, this neatly leads into the Quanba cypress.