Tetraclinis articulata (arartree) description

Tetraclinis articulata

(Vahl) Masters 1892

Common names

Araar tree, alerce, sandarac gum tree, Barbary arborvitae, Mediterranean alerce, citron, African juniper; عرعار ar-ar [Arabic]; thuya d'Algérie, thuya de Barbarie, bois de titre [French]; טטרקליניס מפריק [Hebrew]; gharghar [Maltese]. Historically, it has had many other names; some say the Greek name was θύϊνος (thuinos), "fragrant wood", and others say it was θύον (thuein), "wood of sacrifice." Perhaps, in a bit of word play, it was both, for it was used in both ways: burnt for its odor, and used in woodworking for its fiery hues and textures. In Rome it was citrum, commonly translated as "citrus wood." In 15th century England it was "thyine wood" (Wikipedia, accessed 2022.12.28), and most modern Bible translations render it as "citron" or "thyine," but when the wood is sold, it is most often as "thuya."

Taxonomic notes

The monotypic genus Tetraclinis Masters 1892 joins Calocedrus, Microbiota and Platycladus in a clade within the Cupressaceae, sister to the Cupressus+Juniperus clade (Gadek et al. 2000). Synonyms for T. articulata include Thuja articulata Vahl 1791, Callitris quadrivalvis Rich. et A. Rich. 1826, Cupressus articulata (Vahl) Forbes 1839, and Callitris articulata (Vahl) Murb. 1900. Type: N Tunisia: Hammam-el-Lif (Farjon 2005).

Description

Monoecious evergreen shrubs, or trees to 15 m tall and 50 cm dbh, often multistemmed or forked, coppicing from the base, with long, crooked branches forming a pyramidal crown that soon becomes irregular. Bark rough, fissured, platy, light brown weathering gray. Twigs articulate, branching alternately at various angles, current growth 1-2 mm thick at the ends. Leaves scale-like, decussate, in whorls of 4 on current growth twigs, long decurrent with a free apex, 1.6-8 × 1-1.5 mm, sometimes longer on older twigs, light green with a smooth abaxial surface, weakly dimorphic: the facial leaves linear with a broad, acute apex, partly covered near the base by the linear-spathulate, transverse-convex lateral leaves; stomata in two lateral bands on facial leaves, sparse on lateral leaves. Pollen cones terminal, solitary, ovoid, 4 × 2.5 mm, reddish maturing yellow-brown. Seed cones terminal, solitary to clustered, maturing in 1 year, sub-tetragonal, 10-13 × 13-17 mm, glaucous maturing purplish brown or light brown, with 4 decussate bract-scales of nearly equal size, the scales thick and woody, 10-12 × 8-12 mm, lower pair widest. Seeds 4-6 per cone, conical-triangular, 4-5 × 3 mm, brown with dark spots, with 2 large wings ca. 10 × 6 mm (Farjon 2010).

Distribution and Ecology

N Algeria, Malta, Morocco, S Spain, N Tunisia. In Malta and Spain only tiny relict populations remain (Farjon 2005). Reports from Libya have not been verified. It is also reported to have naturalized in "Palestine" (POWO 2022, accessed 2022.12.28) and iNaturalist observations (accessed 2022.12.28) on Cyprus appear to represent naturalized plants. The species grows in semiarid and winter-rainy parts of the Atlas Mountains, and otherwise at scattered locations in coastal hills, often on limestone, usually amidst maquis vegetation. On southern aspects it occurs to 1800 m elevation, and on northern aspects to 1300 m. Common associates include Pistacia lentiscus, Quercus ilex, and Juniperus phoenicea, occasionally into the lower Cedrus atlantica zone; in Algeria it is an important component of communities dominated by Pinus halepensis and Juniperus oxycedrus (Bencherif and Bellifa 2017). The habitat is often degraded by anthropogenic disturbances including fire, woodcutting, and browsing by livestock; Tetraclinis often survives these through its coppicing ability. Some of the old coppice stools may be very ancient, but have not been dated (Farjon 2010).

Although the species as a whole is not of conservation concern, the Maltese and Spanish populations are listed as "Endangered" by the IUCN. These populations have an area of occupancy of only 72 km² at 6 locations. Subpopulations in both countries have been severely fragmented by urban and agricultural development and fires, and probably lack any effective genetic exchange. Although conservation actions have recently had beneficial effects on the population, all subpopulations are very limited by available habitat, and in most locations and subpopulations there is evidence of a decline in the quality of habitat (Thomas 2017).

Zone 10 (cold hardiness limit between -1°C and +4.4°C) (Bannister and Neuner 2001).

Remarkable Specimens

With regard to very large trees, the only measurement I have seen reported is 18.6 m tall and 40 cm dbh (61 feet tall by 49 inches girth) for a tree at the Arboretum of the University of California, Davis (Arthur L. Jacobson e-mail 2007.08.24). I have seen many photos of trees in habitat, but none appear to rival the California specimen.

With regard to very old trees, some of the old coppice stools may be very ancient, but they have not been dated (Farjon 2010).

Ethnobotany

Tetraclinis has a recorded history of human use reaching back for more than 2000 years. That use has nearly all revolved around two products. One is a resin that exudes from cuts made in the bark and dries into small golden droplets; the second is the wood, with timber used in ancient times but through most of history, a largely subterranean burl associated with coppice stools. The burls grow beneath the ground, and due to their high resin content are often recovered as subfossil wood in areas where the living trees have long been extirpated. In this respect they constitute a non-sustainable resource comparable to subfossil Agathis australis.

The earliest references to Tetraclinis wood come from Homer (ca. 700 BC), as recounted in the writings of the Roman historian Pliny the Elder: "It was known to Homer even, and in the Greek it is known by the name of thyon, or sometimes thya. He says that the wood of this tree was among the unguents that were burnt for their pleasant odour by Circe" (Bostock 1855, Chapter 30). Pliny also cites Theophrastus (ca. 300 BC) in declaring that the rafters of ancient temples were made of this wood due to its decay resistance, evidence that at that time sizable trees were still being harvested for lumber; Theophrastus states that the wood principally came from Cyrenaica, which is now eastern Libya (Bostock 1855, Chapter 30). Writing in ca. 75 CE, Pliny said that Algeria’s Tetraclinis forests had already been fully exploited, with timber coming mainly from Morocco (Bernabei et al. 2019). Morocco has since remained the principal commercial source of Tetraclinis. Both timber and burl wood were extensively used in construction by the Romans (Stevens 2000). Pliny, in his Natural History, discusses at some length the Roman mania for tables made from the burl, noting for instance that Cicero purchased one such table for 1,000,000 sesterces (Bostock 1855, Chapter 29); this was a princely sum, which today would pay for a rather large yacht; and Pliny mentions even more costly tables. The wood is also referred to in the Bible, in Revelations 18.12 (written ca. 100 CE), where it is referred to as citron wood. This is the only Bible reference to it.

In the modern world, Tetraclinis lumber is so scarce as to be nonexistent, but burl wood continues to be harvested (or perhaps I should say mined), chiefly in Morocco, and is used to make small decorative items such as pens and jewelry boxes; for example, many such items can be seen on etsy.com (accessed 2022.12.29). This page from an American burl supplier provides more photos and information, including an interesting tale about importing burl to the USA: Thuya Burl, accessed 2022.12.28.

The other product of Tetraclinis, its resin, has an even richer history. As with the wood, the resin has had many names, but is most commonly called sandarac. Sandarac, though, is not necessarily pure Tetraclinis resin. Ancient writings, such as of Pliny the Elder (Bostock 1855), give hints that pine resins may have been mixed into sandarac, and modern studies performed to support archeological investigations have found evidence that sandarac may have been mixed with juniper resins, such as extracts from Juniperus oxcedrus or J. communis, or that it may have been mixed with or alternately used with the resin of the terebinth tree, Pistacia terebinthus. In medieval times it may have also been mixed with or replaced by various Pinaceae resins, particularly a resin from Larix laricina, with Picea abies used as well (Azemard et al. 2017, Fujii et al. 2021, McGovern et al. 1997, Merrifield 1849). Sandarac seems to have been the most desirable and costly of these various resins, such that the alternative resins were used as adulterants or replacements; it is also possibly because pure sandarac varnish, although hard, also tends to be brittle (Merrifield 1849). Sandarac resin melts at about 150°C to a colorless or slightly yellow liquid. Its specific gravity is about 1.04 (Hurst 1901 in Wikipedia, "sandarac"). It is soluble both in alcohol and in oils, with solution in hot linseed oil most commonly used to create a varnish (Merrfield 1849). As an incense, it is said to be mildly scented, comparable to balsam.

Pliny (cited above) was a bit ambiguous as to whether wood or sandarac were burned as incense in the time of Homer (ca. 700 BC). By the 1st century CE, sandarac was being used to retard the conversion of wine to vinegar (traditionally it gives the piney flavor to the Greek wine retsina), and possibly to seal the interior of amphorae used to store wine (McGovern et al. 1997, Fujii et al. 2021). During the medieval era, sandarac was widely used by oil painters as a varnish, to prepare surfaces to receive paint and also to achieve visual effects during painting; Titian (Venice, early 16th century) is particularly mentioned, but this use of sandarac seems to have continued for some centuries (Merrifield 1849). Today, sandarac cannot be detected on many old oil paintings; it seems to have been commonly removed during cleaning of the surfaces of many old masters (Azemard et al. 2017). It was also used in the 19th century as a protective varnish, to prevent scratching of the emulsion on photographic negatives and positives; for this use it was again noted as brittle, but very transparent (Carey 1868). It also appears to have been used as an element of varnish compounds prepared by luthiers from Renaissance times to the present, but I have not yet found any precise discussion of such use. A 2022 Instagram seach for #sandarac, however, produced many images of its use by luthiers, but few references to painting or photography.

At some time, probably during the medieval era, sandarac started to also be used as pounce, i.e., a material scattered upon wet ink to dry it quickly. When you read of an early writer "sanding" fresh writing, it refers not to mineral sand, but to sandarac powder. Sandarac was also used, commonly in solution with alcohol, to treat paper so that it had a smoother surface, so that lettering would have clearer, sharper edges (Patricia Lovett 2014, Wikipedia, both accessed 2022.12.29). This use remains current.

Sandarac is still widely available, as pounce, or as dried resin that comes in the form of small golden translucent chips or blebs. Based on merchant advertisements, the primary uses of the dried resin seem to be as incense or as a painting or luthier's varnish.

Tetraclinis is occasionally used as an ornamental, sometimes as a bonsai, sometimes as an outdoor tree. It does well in hot, dry climates and makes an acceptable hedge (Rushforth 1999). However, I have yet to see it planted outside of an arboretum or botanical garden.

The species has also been used a bit in dendrochronological research. Sghaier et al. (2013) used short cores to assess growth rates in uneven-aged stands in Tunisia. Rozas et al. (2021) performed a detailed dendroclimatic study that established the feasibility of identifying rings and cross-dating samples, while also identifying some significant problems: "Intra-annual wood density fluctuations, microrings, missing rings and rings with undefined limits were most abundant at the low-elevation coastal site than at the mountain site." Bernabei et al. (2019) used dendrochronological data to infer patterns of wood importation within the Roman empire.

Observations

There is a readily accessible stand of healthy trees in the foothills of the High Atlas just south of Asni (south of Marrakech) in Morocco. The stand breaks up into smaller dispersed patches as one continues the Oued n'Fiss valley toward the Tizi n'Test Pass, a route that also passes through some fine stands of Cupressus dupreziana var. atlantica (Nick Macer email 2007.11.07).

Tetraclinis is a dominant component of several vegetation types, including Pinus halepensis and Juniperus oxycedrus communities, at Tlemcen National Park in Algeria; see Bencherif and Bellifa (2017) for details.

In the Ida Outanane, a far western outlier of the High Atlas range, Tetraclinis grows with the very local endemic Olea europaea subsp. maroccana, the Moroccan wild olive, at lower altitude and also right up into the mountains where very healthy regeneration can be seen (Nick Macer email 2007.11.07).

Remarks

Tetraclinis is from the Greek for "four beds", referring to the leaves in whorls of 4. The epithet articulata refers to seemingly articulated twigs.

This is the national tree of Malta, where its wild occurrence is restricted to about 100 trees in the northern part of the island of Malta (Stevens 2000).

Citations

Azemard, Clara, Matthieu Ménager, and Cathy Vieillescazes. 2017. On the tracks of sandarac, review and chemical analysis. Environmental Science and Pollution Research 24:27746–54. https://doi.org/10.1007/s11356-017-0522-0.

Bencherif, K., and M. Bellifa. 2017. The expected impact of climate change on forest species composition in the national park of Tlemcen-Algeria. Agriculture and Forestry Journal 1(2): 79–88.

Bernabei, M., J. Bontadi, R. Rea, U. Büntgen, and W. Tegel. 2019. Dendrochronological evidence for long-distance timber trading in the Roman Empire. PLoS ONE 14(12):e0224077. https://doi.org/10.1371/journal.pone.0224077

Bostock, John. 1855. The Natural History. Pliny the Elder. London: Taylor and Francis. Available: Perseus Digital Library, accessed 2022.12.29 (see also Chapter 30 at the same site).

Carey. 1868. A manual of photography. Philadelphia: Benerman and Wilson. Available: Internet Archive, accessed 2022.12.29. Sandarac is discussed on pages 286 to 288.

Gadek, P. A., D. L. Alpers, M. M. Heslewood and C. J. Quinn. 2000. Relationships within Cupressaceae sensu lato: a combined morphological and molecular approach. American Journal of Botany 87(7):1044-1057.

Hurst, George H. 1901. Dictionary of chemicals and raw products used in the manufacture of paints, colours, varnishes and allied preparations. London: Scott, Greenwood & Co. Available: Internet Archive, accessed 2022.12.29. Sandarac is discussed on pages 289 to 290.

Masters, Maxwell T. 1892. List of conifers and taxads in cultivation in the open air in Great Britain and Ireland. Journal of the Royal Horticultural Society of London 14:250. Available: Biodiversity Heritage Library, accessed 2022.12.28.

McGovern, Patrick E., Ulrich Hartung, Virginia R. Badler, Donald L. Glusker, and Lawrence J. Exner. 1997. The Beginnings of Winemaking and Viniculture in the Ancient Near East and Egypt.” Expedition: The Magazine of the University of Pennsylvania 39(1):3–21.

Merrifield, Mary P. 1849. Original treatises, dating from the XIIth to the XVIIIth centuries, On the arts of painting... Vol. 1. London: John Murray. Available Internet Archive, accessed 2022.12.29. Sandarac is primarily discussed on pages CCXLVIII to CCLXIII.

Rozas, Vicente, Ana I. Garcia-Cervigon, Miguel Garcia-Hidalgo, Erik Rodriguez-Garcia, and Jose M. Olano. 2021. Living on the edge: Legacy of water availability on Tetraclinis articulata secondary growth under semiarid conditions in Morocco. Dendrochronologia 68:125853.

Rushforth, K. 1999. Trees of Britain and Europe. London: Collins.

Sghaier, T., Margarida Tome, J. Tome, M. Sanchez Gonzalez, Isabel Cañellas Rey de Viñas, and R. Calama. 2013. Distance-independent individual tree diameter-increment model for Thuya [Tetraclinis articulata (VAHL.) MAST.] stands in Tunisia. Forest Systems 22(3):433-441.

Stevens, D. 2000. The Maltese national tree - the araar tree. http://www.geocities.com/rainforest/andes/2113/arartree.html?200712, accessed 2007.11.12, now defunct.

Thomas, P. 2017. Tetraclinis articulata (Europe assessment). The IUCN Red List of Threatened Species 2017: e.T30318A95804470. https://www.iucnredlist.org/species/30318/95804470, accessed on 2022.12.28.