Asunaro (Thujopsis dolabrata): Characteristics, History & Care Guide
Asunaro is a well-known native conifer of Japan. This guide includes identification features, bark, flowers, cones, and photographs taken in Japan.
What Is Asunaro?
Asunaro is an evergreen coniferous tree endemic to Japan, distributed across a wide range from the Oshima Peninsula in Hokkaido to the Osumi Peninsula in Kyushu. It naturally favors moist, fertile soils in deep mountain forests, though it is also widely cultivated. The Asunaro populations of Aomori and Ishikawa Prefectures are especially well known, with Aomori designating it as the official prefectural tree.
Overview
| Item | Description |
| Scientific Name | Thujopsis dolabrata |
| Common Name | Asunaro / Hiba Arborvitae |
| Japanese Name | Asunaro (アスナロ) |
| Family | Cupressaceae |
| Native Range | Japan (endemic) |
| Plant Type | Evergreen Coniferous Tree |
| Height | 20–30 m (65–100 ft) |
| Flowering Season | April–May |
| Fruit Type | Cone |
| USDA Zones | 5–7 |
| Sun Exposure | Partial Shade to Full Sun |
Foliage
Asunaro’s leaves resemble those of Hinoki cypress, which is why it is sometimes referred to as Hiba (桧葉). However, each leaf segment measures 5–7 mm — noticeably larger and thicker than Hinoki’s, with blunt rather than pointed tips. Among scale-leaved conifers, Asunaro has the largest leaves of all, and remarkably, leaves are notably long-lived and may persist for many years.
The white markings on the underside of the leaves (stomatal bands) are another distinguishing feature, making Asunaro relatively easy to tell apart from similar Hiba-type conifers. Numerous branches spread horizontally in layered tiers, giving the tree an overall pyramidal form.
Flowers & Cones
Asunaro is monoecious, producing inconspicuous flowers from April to May. Male flowers are slender and oval-shaped, while female flowers resemble small pinecones covered in thick scales. In its natural habitat.
The cones are oval, measuring 1–1.5 cm in diameter — distinctly different from the nearly perfectly round cones of Hinoki Cypress. Asunaro cones feature small horn-like projections on their scales and ripen around October to November.
Trunk & Bark
The trunk grows straight and can reach up to 1 m in diameter. The bark is reddish-brown to grayish-brown — similar to Hinoki Cypress, but paler in color. With age, the bark splits and peels in vertical strips, though these strips are narrower than those of Hinoki. The bark has traditionally been used for roof thatching.
Garden Use & Historical Significance
Despite its name recognition, Asunaro is not commonly planted as an ornamental garden tree — it has historically been valued far more for its timber. During the Edo period, it was strictly protected by the Tokugawa Shogunate as one of the “Five Precious Trees of Kiso” (Kisogo Boku), alongside Hinoki Cypress, Sawara Cypress, Kurobe, and Japanese Umbrella Pine. In commercial timber trade, the term hiba generally refers to both Asunaro and its variety, Hinoki-Asunaro.
Timber & Practical Uses
Asunaro timber is highly valued for its quality, moisture resistance, and natural resistance to termites. It is widely used in construction (particularly for structural foundations), as well as for bathtubs, interior elements such as ornamental pillars and lintels, Buddhist statues, furniture, and lacquerware — including the famous Tsugaru-nuri lacquerware of Aomori Prefecture. Its fragrance closely resembles that of Hinoki Cypress, and in the Tohoku region — where Hinoki is scarce — Asunaro is often used as a direct substitute.
Name Origin
The name Asunaro carries the meaning “a tree with thick leaves like Hinoki” or “a noble tree like Hinoki.” It is written in Japanese using the characters 明日檜 or 翌檜 — literally, “tomorrow’s Hinoki.”
The most popular interpretation of the name comes from the phrase “asu wa hinoki ni narou” (“tomorrow, I will become a Hinoki”) — a poetic comparison likening the tree, valued less than Hinoki as timber, to a person who hasn’t yet succeeded but strives to improve. This phrase is often used as a life lesson about perseverance and self-improvement. In reality, however, Asunaro never actually grows into Hinoki Cypress — the two remain distinct species throughout their lives.
Growing Guide
Light Requirements
Asunaro is notably shade-tolerant and is known to form pure natural stands on shaded, north-facing slopes. Young trees in particular thrive growing in the dim understory of dense forests.
Pruning
Branches and foliage grow densely, but young trees grow slowly, reducing the need for frequent pruning. The species also tends to respond poorly to heavy pruning, so a light touch is recommended.
Climate Tolerance
Asunaro is cold-hardy but does not tolerate dry conditions well. Consistent moisture is important for healthy growth.
Pests & Disease
Pest and disease problems are rare, though Asunaro can occasionally be affected by witches’ broom disease, which causes the foliage to develop a tangled, seaweed-like appearance.
Cultivars
| Cultivar | Feature |
|---|---|
| Fuiri Asunaro (Variegated Asunaro) | Foliage marked with white variegation |
| Hinoki-Asunaro | A natural variety with slightly smaller leaves and cones than standard Asunaro; cones are perfectly round rather than horned. Native from southern Hokkaido to central Honshu. Essential oil is extracted from its branches and foliage for aromatherapy use. |
| Hime-Asunaro | A dwarf cultivar of Hinoki-Asunaro, bred for garden use. Grows in a multi-stemmed, clumping form and is popular for shaded hedges and topiary. A variegated form also exists. |
How to Tell Asunaro Apart from Hinoki Cypress
As noted above, Asunaro’s leaves are noticeably thicker than Hinoki’s — a difference easy to detect simply by touch. For a more reliable comparison, examine the underside of the leaves: the white stomatal markings on Asunaro and Hinoki have completely different shapes, making this the most definitive way to distinguish the two species.
Frequently Asked Questions
Q: Is Asunaro the same as Hiba?
Not exactly. Hiba is a general term sometimes used for Asunaro, its variety Hinoki-Asunaro, or even other conifers like Kurobe, depending on the region. Commercially, “hiba wood” typically refers to Asunaro and Hinoki-Asunaro specifically.
Q: Does Asunaro really turn into Hinoki Cypress?
No. Despite the name’s literal meaning (“tomorrow’s Hinoki”), Asunaro and Hinoki Cypress are distinct species. Asunaro never transforms into Hinoki — the name is symbolic, often used as a metaphor for personal growth and perseverance.
Q: How can I tell Asunaro and Hinoki Cypress apart?
The easiest way is by touch — Asunaro’s leaves are noticeably thicker. For certainty, check the white markings on the underside of the leaves; the shape differs distinctly between the two species.
Q: Is Asunaro a good choice for home gardens?
It can be, particularly shade-tolerant cultivars like Hime-Asunaro, which are well-suited for hedges and topiary in shaded areas. However, standard Asunaro is more commonly grown for timber than as an ornamental tree.
Q: Where does Asunaro grow naturally?
It is native to Japan, ranging from the Oshima Peninsula in Hokkaido to the Osumi Peninsula in Kyushu, with particularly notable populations in Aomori and Ishikawa Prefectures.
Q: Is Asunaro wood rot-resistant?
Yes. Asunaro wood is highly resistant to decay, moisture, and termites, making it valuable for construction and outdoor use.
Q: Why is Aomori Hiba famous?
Aomori Hiba is renowned for its durability, pleasant fragrance, and natural antibacterial properties. It has been widely used in traditional architecture and woodworking in northern Japan.
Q: Is Asunaro shade tolerant?
Yes. Asunaro is one of the most shade-tolerant Japanese conifers and can grow successfully beneath a forest canopy.
Conclusion
Asunaro (Thujopsis dolabrata) is one of Japan’s most distinctive native conifers, valued for its durable timber, fragrant wood, and exceptional shade tolerance. Although often overshadowed by the more famous Hinoki Cypress, it has played an important role in Japanese forestry, architecture, and traditional craftsmanship for centuries. From the forests of Aomori to cultivated gardens across the country, Asunaro remains a symbol of resilience, patience, and quiet beauty — qualities reflected in the enduring meaning of its name.