Thuja sutchuenensis Seeds | Sichuan Thuja
LATIN NAME: Thuja sutchuenensis
COMMON NAME: Sichuan Thuja
Plant Profile
Thuja sutchuenensis was described from dried material and then disappeared from view for most of a century. The French missionary Paul Farges collected it in 1892 and again about 1900, after which it was assumed to have gone from the wild and was written into the literature as a ghost. Then, in 1999, a Chinese survey team working the limestone country of Chengkou in northeastern Chongqing found living trees on cliff faces. The species had not become extinct; it had been growing on ledges nobody had thought to search.
The foliage grows in flattened sprays arranged in fans, with small scale-like leaves pressed close to the twig and each spray carrying a pale, almost white stomatal band along its underside. The bark is reddish brown and peels in narrow strips. The tree is smaller and finer in all its parts than the western thujas and keeps a narrow, upright outline. Seed cones are small and leathery, ripening from green to brown in a single season and releasing winged seed.
The wild habitat is unpromising and very specific: steep limestone faces, thin pockets of dark soil, and narrow ridgelines at middle elevation, in a cool, humid, monsoonal climate with heavy summer rain and cold winters. The trees cling where few competitors can establish, which is precisely why the species survived and why it was overlooked.
Compared with the western thuja, the cones here carry fewer scales and the sprays are more delicate; compared with the oriental arborvitae, now placed in a separate genus, the foliage is arranged differently and the cones differ in form. The Chinese plants also show a distinctly narrow crown that stays compact in cultivation.
Sequence data have been used to measure how much diversity survives in the remaining trees and how the stands relate to one another, information that decides where reintroduction material may safely be planted. The broader lesson from this tree is that a species thought extinct for decades can persist in terrain that survey teams simply have not visited.
Science & Biotechnology
The rediscovery transformed the tree’s status from presumed lost to merely extremely rare. Survey work mapped the remaining stands and established that the species is confined to a small area of ridge and cliff country. Seeds were collected from documented trees and distributed to botanical gardens, and ex situ populations now underpin both research and reintroduction planting.
Cedar-leaf oils run on monoterpenes, and the thujas are the classic source of thujone, the ketone responsible for the reputation of wormwood and absinthe. Analyses of the leaf oil of this species have reported thujone among the main constituents, together with sabinene, terpinen-4-ol and related alcohols and hydrocarbons. Thujone is neurotoxic in quantity, which is why the oil is studied for insect-repellent and antimicrobial activity rather than swallowed.
Uses & Benefits
Space hedging plants 45 to 60 cm apart and specimen trees two to three metres apart. Water well for the first two summers and mulch with compost each spring. Clip hedges twice in the growing season, never into old bare wood, and shake heavy snow off upright forms in winter, because the narrow crown splits where the load sits. Feed once in spring and avoid high-nitrogen dressings.
Growing from Seed
A species reduced to a small number of stands has a narrow genetic base, and multiplying it from seed alone risks losing what variation remains. Cutting propagation and in vitro culture allow individual trees to be duplicated, so a collection can be built from several wild genotypes rather than one lucky find.
In cultivation the Sichuan thuja behaves as a compact, upright evergreen suitable for hedging, for a windbreak and for specimen planting, though its rarity means it is grown mostly by collectors and conservation gardens. The wood is light, aromatic and resistant to decay, and has been used locally for construction and small carved articles.
Use a mix of two parts lime-free composted bark, one part coarse leaf mould and one part sharp grit. Thuja seed is thin and should be sown on the surface, barely covered, with a thin top-dressing of fine grit to hold it in place and keep the collar dry.
Keep the pan in a cold frame with the lid cracked for ventilation, in bright light but out of hard sun, and water from below with rainwater. Once the seedlings have made a full season of growth and stand around 10 cm, prick them out into deep pots of the same mix and grow them on for a further season before planting out.
Watch for bagworm cases and for spider mites in hot, dry spells, both of which show up first on the inner sprays. Phytophthora root rot is the serious risk, and it follows poor drainage, so plant on a slight mound if your soil holds water. Deer browse the foliage in hard winters.
Our Take
Few plants carry this kind of story, and growing it is a small act of housekeeping for a species that nearly slipped away. The common thujas are useful comparisons and companions: northern white cedar, the tall western red cedar and the hedging oriental arborvitae. Plant it in deep, drained ground, keep it out of standing water, and give it shelter from the worst wind.
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