Liriodendron is a genus in the magnolia family (Magnoliaceae) consisting of two species of large deciduous trees, one native to eastern North America, the other to China. The standard English name is variously given as two words (tulip tree, the most common form in popular usage), hyphenated (tulip-tree), or compound (tuliptree, the most common form in botanical usage).
These trees are easily recognized by their leaves, which are very unusual, having four lobes in most cases and a cross-cut notched or straight apex; size varies from 8-17 cm (3-7 inches) long and 6-12 cm (2.5-5 inches) broad in both species; the petiole is 4-10 cm (1.6-4 inches) long. Leaves on young trees tend to be more deeply lobed than those on mature trees (see photos, left). In autumn the leaves turn yellow, or yellow and brown.
The flowers are 4-8 cm (1½-3 inches) in diameter and have nine tepals, three short outer sepal-like, and six inner petal-like, all yellow-green in colour. They are superficially similar to a tulip in shape, hence the tree's name. The stamens and pistils are arranged spirally around the spike; the stamens fall off, and the pistils become the samaras. The fruit is a cone-like aggregate of samaras, each of which has a roughly tetrahedral seed with one edge attached to the central conical spike and the other edge attached to the wing.
The best known is the American Tulip Tree, L. tulipifera, native to eastern North America from southern Ontario and Vermont south to central Florida and Louisiana. It can grow to more than 50 m (165 feet) in virgin cove forests of the Appalachian Mountains, often with no limbs until it reaches 25-30 m (80-100 feet) in height, making it a very valuable timber tree. It is fast-growing, without the common problems of weak wood strength and short lifespan often seen in fast-growing species. The flowers have an orange band on the tepals; they yield large quantities of nectar and the species is a major honey plant in the eastern United States, yielding a dark reddish, fairly strong honey. It is also called the Tuliptree Magnolia, or sometimes confusingly, "tulip poplar" or "yellow poplar" (though it is not a poplar, family Salicaceae). The American Tulip Tree is the state tree of Indiana, Kentucky and Tennessee.
It has been introduced to many temperate parts of the world, at least as far north as Oslo, Norway. In Canada, it is native to that part of Ontario south of a line from Hamilton to Sarnia, with many specimens in Rondeau Provincial Park, but most cultivation is seen in British Columbia. There, it has been planted on the Queen Charlotte Islands, and in the southern interior as far north as Vernon. Its easternmost cultivation is at Creston. It is common in southwestern cities such as Burnaby, New Westminster, Port Alberni, Vancouver and Victoria. In the Southern Hemisphere, it is cultivated in parts of Argentina, Australia, Chile, New Zealand, South Africa, and Uruguay.
Less well-known is the Chinese Tulip Tree, L. chinense. This native of central and southern China grows in the provinces of Anhui, Guangxi, Jiangsu, Guizhou, Hubei, Hunan, Jiangxi, Shaanxi, Zhejiang, Sichuan and Yunnan. It is very similar to the American species, differing in the often slightly more deeply-lobed leaves, and in the shorter inner tepals in the flower, which lacks the orange pigment of L. tulipifera. The maximum size of the Chinese tulip tree is not known due to a long history of overcutting in its native forests; in cultivation it grows as fast as the American tulip tree, but has not been cultivated long enough to determine its potential mature size, with the largest being about 30 m tall so far. It is not as hardy as the American species, but has been successfully introduced to England, Ireland, Belgium and the Netherlands. In North America, it grows as far north as Boston, Massachusetts in the east and Vancouver, Canada in the west.
Tulip trees make magnificently-shaped specimen trees, but are very large, growing to about 35 m (115 feet) in good soil. Like other members of the Magnolia family, they have fleshy roots that are easily broken if handled roughly. Transplanting should be done in early spring, before leaf-out. Most tulip trees are intolerant of prolonged inundation; however, a coastal plain swamp ecotype in the United States is relatively flood-tolerant. This ecotype is recognized by its blunt-lobed leaves, which may be a reddish blush color. Parts of east-central Florida near Orlando are home to a semi-evergreen ecotype that flowers much earlier (sometimes in February) than other varieties, which usually bloom in mid or late spring.
The soft, fine-grained wood is universally known as "poplar" (short for "yellow poplar" in the U.S., but marketed abroad as "American tulipwood" or by other names). It is very widely used where a cheap, easy-to-work and stable wood is needed, but not a strong or a good-looking wood. It is clearly the wood of choice for use in organs, due to its ability to take a fine, smooth, precisely-cut finish and so to effectively seal against pipes and valves. It is also commonly used for siding clapboards. Its wood may be compared in texture, strength, and softness to white pine.
Like many "Arcto-Tertiary" genera, Liriodendron has become naturally extinct in Europe due to large-scale glaciation. It is known widely as fossils in Europe and well outside its natural range in Asia and North America, showing a once circumpolar distribution.
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