Tetraclinis is a genus of evergreen coniferous tree in the cypress family Cupressaceae, containing only one species, Tetraclinis articulata, also known as Thuja articulata, sandarac, sandarac tree or Barbary thuja, endemic to the western Mediterranean region. It is native to northwestern Africa in the Atlas Mountains of Morocco, Algeria and Tunisia, with two small outlying populations on Malta, and near Cartagena in southeast Spain. It grows at relatively low altitudes in a hot, dry subtropical Mediterranean climate.
Its closest relatives are Platycladus, Microbiota and Calocedres, with the closest resemblance to the latter. In older texts, it was sometimes treated in Thuja or Callitris, but it is less closely related to those genera.
It is a small, slow-growing tree, to 6–15 m (rarely 20 m) tall and 0.5 m (rarely 1 m) trunk diameter, often with two or more trunks from the base. The foliage forms in open sprays with scale-like leaves 1–8 mm long and 1–1.5 mm broad; the leaves are arranged in opposite decussate pairs, with the successive pairs closely then distantly spaced, so forming apparent whorls of four. The cones are 10–15 mm long, green ripening brown in about 8 months from pollination, and have four thick scales arranged in two opposite pairs. The seeds are 5–7 mm long and 2 mm broad, with a 3–4 mm broad papery wing on each side.
It is one of only a small number of conifers able to coppice (re-grow by sprouting from stumps), an adaptation to survive wildfire and moderate levels of browsing by animals. Old trees that have sprouted repeatedly over a long period form large burls at the base, known as lupias. It is the National tree of Malta and is now being used locally in afforestation projects.
The resin, known as sandarac is used to make varnish and lacquer, it is particularly valued for preserving paintings.
The wood, known as thuya wood or citron wood, and historically also known as thyine wood, is used for decorative woodwork, particularly wood from burls at the base of the trunk. Use of the burl wood kills the tree. The market in Morocco is unsustainable, focusing as it does on the burl, and has resulted in mass deforestation of the species. The species is also threatened by overgrazing, which can kill the coppice regrowth before it gets tall enough to be out of the reach of livestock.