Xanthocyparis vietnamensis Seeds | Vietnamese Golden Cypress
LATIN NAME: Xanthocyparis vietnamensis
COMMON NAME: Vietnamese Golden Cypress, Vietnamese Cypress
Plant Profile
Finding an undescribed conifer genus is not something that happens often, and it happened here in 2002, when a cypress from the limestone mountains of northern Vietnam was described as a genus new to science. The tree had been noticed only a few years earlier during survey work in Ha Giang, and its formal publication came with a second surprise: the same genus was said to include the Nootka cypress of western North America, an ocean away. The name means yellow cypress, and the reason is visible in the foliage.
Young plants carry soft, needle-like leaves that look nothing like the adult foliage, and the changeover from juvenile to mature form is gradual rather than abrupt, which is one of the characters that set the genus apart. Adult branchlets are flattened into sprays of small scale leaves, yellowish green at the best of times and distinctly golden in new growth, especially in sun. Small round cones sit on short stalks, ripening on the tree. The crown is conical and the tree reaches about fifteen metres on a good site.
The wild habitat is limestone karst: ridges, cliff edges and steep slopes of weathered rock with pockets of thin, alkaline soil, in a cool, wet, montane climate with mist and heavy summer rain, where vegetation is stunted and open. The species is known from a very small number of sites, which places it among the most threatened conifers.
The flattened sprays and the dimorphic foliage make it look like a false cypress, while the cone structure and the scale arrangement align it with the true cypresses. What is truly distinctive is the combination: juvenile needles that persist on young shoots, adult sprays of the Chamaecyparis type, and peltate cone scales of the Cupressus type, all on one tree.
Science & Biotechnology
The genus was proposed together with the transfer of the Nootka cypress out of Chamaecyparis, creating an amphi-Pacific pair: one species in Vietnam, one on the Pacific coast of North America, and nothing in between. Later molecular work has been unkind to that tidy picture, returning the Nootka cypress to its own genus Callitropsis and leaving the Vietnamese species either alone in Xanthocyparis or placed in Cupressus depending on the author.
Genomic work on a plant this rare is awkward: sampling has to be minimal and non-destructive, and the results are read against a narrow baseline. Plastid and nuclear sequences have nonetheless been used to place the species among the New World cypresses, to test the relationships of the isolated stands, and to estimate how long ago the two sides of the Pacific split.
Cypress foliage oils are mixtures of monoterpene hydrocarbons, and analyses of this species report the familiar set of pinene, limonene and sabinene together with oxygenated compounds and sesquiterpenes. The composition is what you would expect from a member of the family rather than a chemical curiosity; its interest lies in the comparison with the North American relatives.
Uses & Benefits
There is no wood trade, no oil trade and no historic garden tradition behind this tree. Its uses are conservation, research and ornamental planting in nearly frost-free gardens, where the golden foliage carries through the year and makes a bright, narrow specimen for a sheltered courtyard. In Vietnam it is protected within the reserve system established around its habitat.
Growing from Seed
Roots of a karst conifer rot in rich, wet compost, so the medium must drain hard: two parts coarse grit, one part fine lime-free bark compost and one part leaf mould. Sow the seed on the surface and cover it with a shallow layer of grit.
Keep the pan in a cold frame under light shade, watering from below and letting the surface dry between waterings. Grow the seedlings on in deep, narrow pots, and plant out when they are around 30 cm tall, on a slight mound of gritty soil so that water never sits at the collar. Space specimen plants three to four metres apart.
Because the wild population is tiny, cuttings are the responsible way to multiply a particular genotype. Take semi-ripe shoots from young, vigorous growth in late summer, trim them to a short heel, wound the base and set them in a gritty mix under mist or in a closed case with gentle bottom heat. Rooting is slow.
Frost tolerance in the cultivated stock is still being learned, so give young plants a sheltered frame or a wall for the first winters and be ready to wrap them. Feed once in spring with a slow-release dressing balanced for evergreens, mulch with grit rather than compost to keep the collar dry.
Our Take
Grow it in a pot for a few years before you trust it to the open ground; that way one cold night does not cost you the plant. If you want to build a collection of rare cypresses, the warm-temperate Cupressus torulosa, the Mediterranean Italian cypress and the Chinese weeping cypress are natural companions, and they take similar drainage. Sharp drainage and a warm wall will do more for this tree than feeding.
Related Reading
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