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WHITE MULBERRY
Morus alba
Family: Mulberry Family (Moraceae)
Other Names: mulberry, Russian mulberry, silkworm mulberry.
Origin and Distribution: White mulberry is native to China and has long been cultivated in Europe. The British introduced it to North America prior to the American Revolution in a failed attempt to establish a silkworm industry, since the leaves are the primary food of silkworm caterpillars. Several varieties of this species have been widely planted in North America and have become naturalized. White mulberry is common in the eastern U.S., and is found in over three-fourths of the counties of Ohio, mostly along fencerows of unattended areas and in other open rural and urban habitats. It is not tolerant of shade and rarely grows in forested sites. But it is relatively tolerant of drought, salt, pollution and poor soils. This species is increasingly found in no-till corn or soybean fields where it may interfere with harvest.
Plant Description: White mulberry is a small- to medium-sized, fast-growing, deciduous tree with a short, thick trunk that branches into numerous limbs to form a bushy, spreading crown. Several varieties exist, and they may have erect or weeping branches. This species is characterized by its furrowed orangish-brown bark, slender light orange twigs, shiny variously-lobed leaves and white to pink to purple berry-like fruit. In field crops, young trees are cut off annually by harvesting equipment and sprout new branches each spring, resulting in a highly branched shrub with a large trunk close to the ground. Twigs and leaves exude a milky juice (latex). The wood is light, soft and coarse-grained. White mulberry reproduces by seeds.
- Root system - White mulberry produces wide-spreading, aggressive roots that are known to clog drains.
- Stems - The trunk is short, thick (8 to 16 inches in diameter, sometimes up to 5 feet) and multi-branched, resulting in a full, spreading crown. Central stems can grow 20 to 50 feet tall (sometimes up to 80 feet), but as a weed of roadsides and crop fields, it seldom grows over 15 feet tall. The bark is gray at first, turning an orangish- or yellowish-brown, with shallow furrows or ridges and an orange inner layer that is visible through the furrows. Secondary branches are generally slender and, depending on the variety, may be upright or hang casually toward the ground. Twigs are slender, erect and initially slightly hairy and reddish-brown, becoming smooth and light orange. Several shoots are produced from one node, giving the crown a branchy appearance.
- Leaves - The thin, bright, light green leaves are alternate, broadly oval and 2 to 4 inches long, with toothed margins (triangular teeth). The upper surface is smooth and shiny. The lower leaf surface is pale green and generally smooth, with hairs only along the main veins. Leaves can be unlobed (common on older trees) or have 2 to 5 unequal lobes (common on young trees and sprouts from older trees). The petiole (leaf stalk) is smooth.
- Flowers - Clusters of small petalless flowers are borne in a dense hanging spike. Male and female flowers are usually produced on separate plants (dioecious), but sometimes are produced on the same plant (monoecious). The male flower cluster is narrow and somewhat elongated and the female flower cluster is more oval.
- Fruits & Seeds - The berry-like ‘fruit’ is a tight, elongated cluster of white to pink (sometimes violet) smaller fruits. There are several horticultural varieties, some with dark fruit.
Similar Species: Red mulberry (Morus rubra) is a larger native version of its cousin, growing to heights of 50 to 70 feet with trunk diameters of 2 to 3 feet. It produces a light soft wood and rough brown bark. The red mulberry is indigenous to the eastern United States, and grows best in rich, river bottom woods and floodplains. Red mulberry is distinguished from white mulberry by the following: its leaves are larger, thicker, less shiny and have a downy lower surface; the bark and twigs are less orange or yellow; the fruits are longer and red to blackish but never white or pink; and it occurs in more natural, shaded habitats such as floodplain forests.
Biology: White mulberry flowers from April to June. Flowers are wind-pollinated. The fruits are very attractive to birds and mammals, which are probably responsible for its spread along fencerows and in fields. The plant has strong rooting ability and cut stems buried in soil are able to regenerate.
White mulberry is a fast-growing, short-lived plant that is becoming a problem in no-till fields. Once established, the roots will continue to produce sprouts even if the plant is cut back every year. White mulberry hybridizes with other Morus species through cross-pollination. This has raised concerns for the native red mulberry, because 'genetic swamping' could eliminate the native species.
Toxicity: All parts of white mulberry, except for the ripe fruit, contain a milky sap (latex) that is toxic to humans. Although humans may consume ripe mulberry fruit, ingestion of unripe fruit can result in stomach upset, stimulation of the nervous system and hallucinations. The sap is also an irritant, and contact with leaves and stems may result in varying degrees of skin irritation. White mulberry pollen is highly allergenic and contributes to hayfever.
Facts and Folklore:
- The genus name, Morus, is Latin for 'delay', referring to the formation of winter buds late in the season after the weather has turned cold. The species name, alba, means 'white', referring to the whitish color of the buds.
- The silkworm is thought to prefer mulberries over all other plants due to a unique fragrance given off by the mulberry and to special organs in the caterpillar that respond to the taste of mulberry leaves. Silk proteins (fibroin and sericin) are derived only from mulberry leaves.
- White mulberry fruits vary greatly in sweetness, some being very sweet and others dry and tasteless. They lack the tartness of other mulberry species.
