Thujopsis dolabrata (Thunb. ex L. f.) Siebold & Zucc.

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Credits

Tom Christian (2021)

Recommended citation
Christian, T. (2021), 'Thujopsis dolabrata' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/thujopsis/thujopsis-dolabrata/). Accessed 2022-06-29.

Genus

Common Names

  • Asunaro
  • Hiba
  • Hiba Arborvitae
  • Hiba Cedar
  • Deephorn Cedar
  • Battle Axe Cedar
  • Lizard Tree

Synonyms

  • Thujopsis dolabrata var. australis A. Henry

Glossary

asl
Above sea-level.
dbh
Diameter (of trunk) at breast height. Breast height is defined as 4.5 feet (1.37 m) above the ground.
family
A group of genera more closely related to each other than to genera in other families. Names of families are identified by the suffix ‘-aceae’ (e.g. Myrtaceae) with a few traditional exceptions (e.g. Leguminosae).
montane
Of mountains.
variety
(var.) Taxonomic rank (varietas) grouping variants of a species with relatively minor differentiation in a few characters but occurring as recognisable populations. Often loosely used for rare minor variants more usefully ranked as forms.

Credits

Tom Christian (2021)

Recommended citation
Christian, T. (2021), 'Thujopsis dolabrata' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/thujopsis/thujopsis-dolabrata/). Accessed 2022-06-29.

Monoecious evergreen tree 10–30(–40) m tall × 0.5–1.5(–2.5) m dbh, densely pyramidal-columnar habit with a spire-like crown, often with multiple stems from the base or with lowest branches layering. Bark dark reddish-brown, smooth or longitudinally fibrous, detaching in long thin stringy layers. Branches irregularly whorled, densely arranged, descending in the lower part of the tree, ascending in the crown and on young vigorous plants. Branchlets distichous, thick, somewhat flattened when young, later rounded, maturing from green to reddish-brown, obscured for several years by persistent scale-like leaves. Scale-leaves thick, leathery, 3–5 mm long, borne all around leading shoots but arranged in fan-like lateral sprays on branchlets, decurrent at the base, the apex of the previous leaf overlapping and obscuring the base of the next; leaves comprise two trapezoid-triangular central scales (adaxial and abaxial), lateral scales hatchet-shaped, keeled, outspreading, incurved at the apex; mid-dark green above with a high gloss, pruinose-white below with prominent green margins. Pollen cones 2–3 mm, ripening in May, blackish, inconspicuous. Seed cones ripening in one season (pollination May, seed disperal October, both by wind), subglobose, 1–1.8 cm with two opposite pairs of fertile scales and 1–2 pairs of infertile scales, with protruding mucros (‘horns’) in the upper parts; blue-grey at first, grey-brown at maturity; 3–5 seeds per fertile scale, scales woody and somewhat persistent. (Debreczy & Rácz 2011Walters et al. 1986Bean 1981).

Distribution  Japan Southernmost Hokkaido and north-central Honshu (var. hondae); central Honshu south to Shikoku and Kyushu (var. dolabrata)

Habitat In a wide range of habitat types with a broad suite of associates, from c. 150–1000 m asl in the north (var. hondae) and between c. 1000–2000 m asl in the south (var. dolabrata), frequent throughout in mixed broad-leaf and coniferous forests, often with Fagus, Thuja standishii and Tsuga diversifolia. It is especially frequent in the snowbelt zone of western Japan. As a secondary succession species commonly forming pure stands, but rarely extensive forests, understoreys typically feature very shade tolerant shrubs such as Aucuba and Skimmia.

USDA Hardiness Zone 5b-6

RHS Hardiness Rating H6

Conservation status Least concern (LC)

Among the bewildering diversity of conifers with scale-like foliage Thujopsis has the happy claim to be, perhaps, the most distinctive. Its densely arranged and overlapping leaves closely resemble those of Thuja (and indeed several other ‘flat-leaved’ Cupressaceae genera) but in Thujopsis nature has kindly magnified this extraordinary form such that the leaves are comfortably the largest and thickest example of these ‘reptilian scales’ (Mitchell 1972) one is likely to encounter in northern temperate gardens. The upper leaf surface is a rich, glossy green, while the underside of each individual scale is covered in chalk-white stomata surrounded by a prominent shining green margin. The effect is intricate, beautiful, and instantly diagnostic, and remains so whatever form this rather variable tree takes on.

Most cultivated trees fall comfortably into one of two categories: multi-stemmed or single-stemmed. Perhaps most are multi-stemmed from the base, with fewer than a handful or as many as thirty very straight stems of broadly comparable size and vigour; single-stemmed trees are obviously so, with long straight boles free of low branches. As is often the case the earliest significant introductions represented these two extremes and horticulture quickly accepted this convenient binary as writ. The passage of time, however, has revealed the prevalence of intermediate forms. Although these account for only a minority of trees, intermediate forms may have a single short bole, with several major branches from low on the trunk that soon take on apical dominance; otherwise, they may have several stems from the base, but one will always be dominant and significantly larger than the others (Mitchell 1996).

Truly single-stemmed trees will usually belong to the northern variety var. hondae, but this is not without exception, and several theories have been put forward to explain the disparity in form. One explanation is ecology: With an extensive range over much of the middle part of the Japanese archipelago, from Kyushu and Shikoku in the south to southern Hokkaido in the north, Thujopsis occurs with a broad range of associates, usually in mixed conifer-broadleaf communities or in coniferous forests, hence it has evolved as a very shade tolerant conifer of secondary succession; its seeds germinate under existing canopy and young plants can survive for long periods in oppressive shade, patiently waiting for a gap to emerge (Nakamura & Krestov 2005). Planted under dense canopy young trees grow slowly and will often remain stubbornly single-stemmed; planted out in the open with plenty of side light, however, young trees can produce extremely dense growth, with side-branches borne from close to the base of the stem. In the right conditions these low side branches will quickly layer and form new leading shoots; when this process is repeated the result will be a multi-stemmed tree. Clearly there is a horticultural choice to be made also: to prune or not to prune a young plant, although this window of opportunity is narrow.

In the southern parts of its range Thujopsis is a montane species, typically occurring from 1000–2000 m asl; in the much-cooler north it occurs below 1000 m, extending even to lowland-coastal forests in northernmost Honshu and southernmost Hokkaido (Debreczy & Rácz 2011). Northern populations have traditionally been distinguished as var. hondae. Besides the rather minor morphological differences used to distinguish var. hondae (larger and desner habit, larger and more globular seed cones lacking pronounced ‘horns’) the northern variety exhibits different ecological traits, too: it is more likely to occur in pure forests and to make larger trees than var. dolabrata (Debreczy & Rácz 2011). Henry Elwes visited the forest at Uchimappe in Aomori Prefecture, extreme northern Honshu and later recounted: ‘…the forest, which consists mainly of Thujopsis naturally reproduced, though here and there, trees of [Quercus serrata and Magnolia obovata], and other species occur, whilst Cryptomeria and [Chamaecyparis obtusa] are planted in the valleys […] The average height of the trees here is about 70 to 80 feet [c. 21–24 m], attaining in deep shady valleys 100 feet [c. 30 m] or perhaps more, and about 2 feet [0.6 m] in diameter when closely grown, at the age of 150 to 180 years when it is considered ripe for felling’ (Elwes & Henry 1906–1913).

Thujopsis is now cultivated throughout the temperate world as an ornamental, including in many parts of China where it may have been cultivated for far longer than in the west (Fu et al. 1999), but its introduction to western cultivation, at least, was chequered. Thomas Lobb, working for the Veitch nurseries, sent a living plant back to England from the Botanical Garden at Buitenzorg (modern Bogor) Java, in 1853. The origin of the stock at Bogor is not recorded, but it was certainly an early (and perhaps dodgy) export from Japan. The sole plant sent by Lobb must have been in a sorry state when it was disembarked at Exeter for it quickly died. The next introduction to England was that of Captain Fortescue, who brought a plant home from Japan soon afterwards. This plant did survive and was planted at Fortescue’s family home of Castlehill, Devon, in 1859, the same year Siebold introduced living material to the Netherlands (Bean 1981; Jacobson 1996). In the early 20th century Elwes made no mention of Siebold’s introduction but reported the Fortescue plant had been dead ‘for some time, though plants raised from its cuttings are still growing at Castlehill and elsewhere’ (Elwes & Henry 1906–1913). The first successful commercial introductions were those made almost simultaneously by John Gould Veitch and Robert Fortune in autumn 1860: Veitch gathered seed of what must have been var. hondae during his stay at Hakodate, in southern Hokkaido, while Fortune gathered seed from a cemetery near Tokyo and sent this to the Standish nursery, thus the two rival firms were able to offer this curious new conifer at the same time (Bean 1981).

From these introductions both seed- and cutting-raised Hiba soon spread throughout gardens and fashionable pineta in Britain and Europe. Remarkably hardy, Hiba will grow in a continental climate providing the summers are not excessively hot: It grows at the Arboretum Mustila in southern Finland, for example, but is limited here, mostly existing in shrub form rarely and exceeding 1–1.5 m tall (mustila.fi). It forms trees in more forgiving areas where the rigours of a continental climate are mitigated by maritime influence, for example at Gothenburg Botanic Garden in Sweden (pers. obs.), or where intense summer heat is counteracted by a cool, understorey position in perpetually moist soils, such as in several gardens around the Italian Lakes (pers. obs.), but the best trees are doubtless those growing in ‘mild winter-cool summer’ areas with year-round precipitation and, crucially, where trees have constant access to moisture throughout the growing season. In some of these areas – the western fringes of Britain, across the island of Ireland, and comparable areas of the Pacific Northwest and parts of New Zealand – Hiba can grow as well as in native forests in Japan.

The largest known in cultivation grow in the UK and Ireland. A remarkable single-stemmed tree in Portmeirion, Wales, was 27.5 m × 0.52 m dbh in 2016. Larger girths are known, notably a tree at Tregrehan, Cornwall, 22 m × 1.16 m in 2014. Much further north, near Ullapool on Scotland’s northwest coast, several remarkable trees grow at Leckmelm, the best of which has multiple stems approaching 0.5 m dbh and rising to a height of 23 m (in 2013) (Tree Register 2021; pers. obs.). Provided it has constant access to moisture Hiba is broadly tolerant of soil type. Several good examples grow on shallow soils over chalk at Pampisford, Cambridgeshire, UK (pers. obs.); now well established with extensive root systems, they must have needed careful tending to establish in soils prone to drying out.

Hiba arrived in North America in the late 19th century, presumably following the significant 1860 introductions to Britain. It is now widely grown here, hardy to zone 5b–6 so long as the conditions suit it, but also able to cope with the hot sticky summers of areas like South Carolina provided it does not dry out. It is at its best, though, in the cooler north-eastern states and especially on the western seaboard, from San Francisco (where it benefits from regular fog) north to Vancouver, and here it is a relatively common sight in public and private gardens alike, though it has neither achieved the prevelance nor the dimensions that it has in western Britain and Ireland; 10–15 m is its typical maximum here (Kennedy 2020). It seems to have generated a curious plethora of common names in North America, far more than it has in Europe; the most prevalent of these are listed above. Among the more curious are Battle Axe Cedar, a reference to the resemblance of the shape of individual leaves to axe-heads, a feature also referenced in Hiba’s scientific name; dolabrata is derived from the Latin dolabra, meaning axe. Lizard Tree, a reference to the scale-like leaves, has never caught on in Britain.

Along with Hinoki (Chamaecyparis obtsua), Sawara (C. pisifera), Koya Maki (Sciadopitys verticillata) and Nezuko (Thuja standishii), Hiba is considered one of the five sacred trees of Kiso in Japanese culture, reserved exclusively for imperial use in ancient feudal Japan (Jones 2020). Venerable trees of considerable size can be seen in gardens and the precincts of temples throughout its range, where it is also utilised as a hedging plant. One such tree (growing in Aomori prefecture and hence belonging to var. hondae) has an enormous single bole, 2.3 m dbh, which very soon breaks into multiple trunks each of considerable size, the tallest reaching 33 m height (2012 measurements; monumentaltrees.com).

Throughout its range Hiba’s versatile timber has been employed in various ways. Elwes noted it was widely used for all manner of purposes and prized for its durability: ‘this is proved by specimens shown at the St. Louis Exhibition, one of which had been used as a gate-post for eighty-three years, another as a plank in a fishing-boat for eighty-four years, others as railway sleepers in use for fourteen years […] Exceptional cases occur in which the wood is curiously mottled and freckled. A ceiling and a screen made of such wood, which I saw in the Forestry Bureau at Aomori, were very beautiful’ (Elwes & Henry 1906–1913). Extensive forests in northern Honshu are still managed for timber and Aomori Hiba continues to be highly prized for specialised uses. Hiba has also been shown to contain the compounds Hinokitiol and Beta-dolobrin, known for anti-bacterial and insect-repellent properties, and essential oils and other products containing these compounds are marketed around the developed world (Inamori et al. 2006).

Returning to horticulture, despite the ease with which cuttings will root Hiba these days is rarely offered and rarely planted in its typical form. Those who would grow it must seek it out from specialist nurseries or raise their own plants from cuttings or seeds. Semi-ripe heel cuttings taken in early autumn, treated with rooting hormone and placed over bottom heat, will root; it is important to select material with some apical dominance, and young plants will still require formative pruning and perhaps staking whilst young (pers. obs.). When siting young plants it is important to bear in mind Hiba’s rather variable and unpredictable habit; cuttings from a single-stemmed tree can easily result in a multi-stemmed one, and although Hiba is never a particular fast-growing tree, in time it can become a large one. Nevertheless, as a beautiful alternative to its more ubiquitous relatives, it is yet another tree deserving of wider appreciation throughout the temperate zone.


'Atrovirens'

Recorded in England by Nelson in 1866, this name was applied to a tree typical of the species but with particularly dark green foliage (Auders & Spicer 2012); this variability is now accepted within the species and the name is superfluous.


'Aurea'

Named by Nelson from material raised in England c. 1866, ‘Aurea’ is slower-growing than typical, to 1.5 m in ten years. The summer foliage is green with widespread gold-yellow variegation; in autumn plants in a sunny position take on a bronze hue (Auders & Spicer 2012). Several comporable cultivars are now in commerce:

  • ‘Aurescens’ Reported from Arboretum Trompenburg in 1987, Auders & Spicer consider this an erroneous re-naming of ‘Aurea’
  • ‘Lutea’ Yellowish-green variegated, but only dubiously distinct from ‘Aurea’
  • ‘Melboune Gold’ In most respects a dwarf form of ‘Aurea’, with the habit of ‘Nana’. Believed to have originated in the UK, it has had only a scarce distribution
  • ‘Solar Flare’ Although raised as a sport from ‘Nana’, this plant has as much in common with ‘Aurea’, having a good golden-yellow colour retained all year round. It was raised in the UK by the late Derek Spicer and introduced in 2013

'Decumbens'

Recorded from Germany by Beissner in 1891, this form is typical of the species but with nodding branches (Auders & Spicer 2012).


Dwarf Cultivars

Several dwarf or semi-dwarf forms of T. dolabrata exist; the distinctions between them are murky at best and those that remain in commerce have likely been confused for many years. ‘Nana’, introduced c. 1861 and possibly directly from Japan, is the oldest name and should probably be used as a Cultivar Group for those that are dwarf or semi-dwarf, and mostly green. Several dwarf plants with yellow or variegated foliage are discussed under ‘Aurea’ and ‘Variegata’ respectively. Cultivar descriptions are principally derived from Auders & Spicer (2012).

  • ‘Elegans’ Described as a compact plant with elegant foliage this selection probably originated in Hungary in the early 2000s, but the cultivar name in Latin form is only acceptable if it was published prior to 1959
  • ‘Laetevirens’ Long thought to be the same plant as ‘Nana’, Auders & Spicer (2012) err to the view that the two are different, based on historic accounts and an extant plant at Hergest Croft, Herefordshire, UK, with ‘distinctly coarser foliage and ‘Nana’ and […] more open’
  • ‘Latifolia’ A low shrub, larger and wider growing than ‘Nana’ with larger leaves than typical which are more tightly adpressed to the shoot
  • ‘Nana’ Described as a ‘semi-dwarf’ plant with an open, flat-topped habit; the foliage is smaller than typical with leaves only 1.5 mm long. In ten years to 40 × 70 cm. Reportedly introduced by Veitch in 1861, it has not been recorded whether he brought this selection back as a plant from a Japanese nursery, or whether it was raised from his seed collection in southern Hokkaido
  • ‘Plicata’ A semi-procumbent plant raised from seed by the Ansorge Nursery, Germany, 1902. Very similar to ‘Nana’
  • ‘Pygmaea’ Reported from the US prior to 1993, but without any known distinctive features

var. hondae Makino

Synonyms
Thujopsis dolabrata subsp. hondae (Makino) Silba

Distinguished from the type by its larger and denser, more arboreal habit, and by its seed cones without prominent mucros (horns) (Debreczy & Rácz 2011).

This variety is discussed generally within the main species article.


'Variegata'

W.J. Bean spoke for many when he called this cultivar with scattered yellowish or white variegation ‘valueless’ (Bean 1981). Although the variegation can be pronounced and striking in youth it usually is not: even when this is the case plants quickly revert and no sizeable trees are known that retain more than a trace of variegation, with just the occaional variegated branchlet obvious at close-hand; from a distance old trees appear typical green (Mitchell 1996). This problem has been exacerbated by careless repropagation: when young plants with good proportion of variegation are propagated the aberrance is perpetuated, but through the generations the effect has been diluted to the brink of pointlessness as nurseries have used too-old trees as stock plants, with the result that even young plants now are only weakly variegated unless they are sourced from a diligent propagator. This form was introduced to the Netherlands by P.F. von Siebold in 1860–61; it is slightly slower-growing than typical forms, to c. 2 m in ten years (Auders & Spicer 2012).

  • ‘Albovariegata’ A plant bearing this name was reported from Windsor Great Park, UK, in 1985. It is no longer known and was probably a mistaken rendering of ‘Variegata’.
  • ‘Cantab’ A variegated dwarf reportedly found in Cambridge Botanic Garden, UK, and introduced to commerce c. 1977. Auders & Spicer suspect it has been lost
  • ‘Krügers Findling’ A slow-growing compact form with good creamy-white variegation introduced by the Horstmann Nurseries, Germany, in 1992. It may be nothing more than a slower sport of ‘Variegata’ which holds its colour longer