White Mulberry

Morus alba, known as white mulberry, is a fast-growing, small to medium-sized mulberry tree which grows to 10–20 m (33–66 ft) tall. It is generally a short-lived tree with a lifespan comparable to that of humans, although there are some specimens known to be over 250 years old. The species is native to northern China, and is widely cultivated and naturalized elsewhere (United States, Mexico, Australia, Kyrgyzstan, Argentina, Turkey, Iran, etc.). The white mulberry is widely cultivated to feed the silkworms employed in the commercial production of silk. It is also notable for the rapid release of its pollen, which is launched at over half the speed of sound. Its berries are edible when ripe. On young, vigorous shoots, the leaves may be up to 30 cm (12 in) long, and deeply and intricately lobed, with the lobes rounded. On older trees, the leaves are generally 5–15 cm (2.0–5.9 in) long, unlobed, cordate at the base and rounded to acuminate at the tip, and serrated on the margins. The trees are generally deciduous in temperate regions, but trees grown in tropical regions can be evergreen. The flowers are single-sex catkins; male catkins are 2–3.5 cm (0.8–1.4 in) long, and female catkins 1–2 cm (0.4–0.8 in) long. Male and female flowers are usually on separate trees although they may occur on the same tree. The fruit is 1–1.5 cm (0.4–0.6 in) long; in the species in the wild it is deep purple, but in many cultivated plants it varies from white to pink; it is sweet but bland, unlike the more intense flavor of the red mulberry and black mulberry. The seeds are widely dispersed in the droppings of birds that eat the fruit. The white mulberry is scientifically notable for the rapid plant movement involved in pollen release from its catkins. The stamens act as catapults, releasing stored elastic energy in just 25 µs. The resulting movement is approximately 350 miles per hour (560 km/h), over half the speed of sound, making it the fastest known movement in the plant kingdom. Two varieties of Morus alba are recognized: Cultivation of white mulberry for silkworms began over four thousand years ago in China. In 2002, 6,260 km2 of land were devoted to the species in China. The species is now extensively planted and widely naturalized throughout the warm temperate world. It has been grown widely from the Indian subcontinent west through Afghanistan and Iran to southern Europe for over a thousand years for leaves to feed silkworms. More recently, it has become widely naturalized in disturbed areas such as roadsides and the edges of tree lots, along with urban areas in much of North America, where it hybridizes readily with the locally native red mulberry (Morus rubra). There is now serious concern for the long-term genetic viability of the red mulberry because of extensive hybridization in some areas.