1. Morus alba L. (white mulberry, silkworm mulberry)

Pl. 458 c, d; Map 2081

Twigs orangish brown to dark green, sometimes reddish-tinged, minutely hairy or nearly glabrous, the lenticels usually darker brown. Petioles 0.7–3.5(–4) cm long. Leaf blades 4–12 cm long, 3–9 cm wide, unlobed or shallowly to deeply 3–5-lobed, abruptly tapered to a sharply pointed tip, the lateral lobes (when present) rounded or broadly angled (occasionally narrowly angled to short-tapered in very deeply lobed blades), truncate to cordate or occasionally broadly rounded at the base, the upper surface smooth or nearly so and often shiny, glabrous or with a few hairs along the main veins, the undersurface with scattered hairs along the main veins Staminate inflorescences 25–40 mm long, cylindric. Pistillate inflorescences 5–8 mm long, short-cylindric to subglobose. Multiple fruits 0.6–1.8 cm long, 0.5–0.7 cm wide, short-cylindric to subglobose, white, red, or purple, the achenes 2–3 m long. 2n=28. April–May.

Introduced, scattered nearly throughout the state, but apparently uncommon in some counties of the Ozark Division (native of Asia, introduced nearly throughout North America, Europe). Bottomland forests, mesic upland forests, banks of streams and rivers, margins of ponds, lakes, sinkhole ponds, and marshes, sloughs, and edges of upland prairies; also ditches, fencerows, gardens, farm yards, railroads, roadsides, and disturbed areas.

White mulberry is one of the most important commercial food plants for silkworms in the silk-producing regions of China. It was introduced to North America before 1620 as a food plant for silkworms, and it is now thoroughly naturalized throughout the eastern United States, as well as in scattered areas across the West. The species became naturalized so long ago that Native Americans used it medicinally as a laxative and purgative, and for the treatment of dysentery (Moerman, 1998). White mulberry was once important on farms as food for pigs and poultry, but in modern homes with no livestock the heavy crops of soft, sweet fruit are a nuisance, especially when the trees overhang paths and driveways. It is difficult to clean up the stains from red- or purple-berried forms, and from the droppings of birds that have fed on them.

Morus alba and M. rubra hybridize where they occur together (Salah, 2006). Hybrids are intermediate betweent the parental species in leaf size and pubescence. A number of horticultural forms of M. alba have been developed. Rehder (1940) and other authors reported strains of this species in cultivation with very large unlobed leaves — reportedly to 22 cm long, far outside the normal size range for the species. These have been called cv. ‘Macrophylla’; they likely are the result of past hybridization with another species of mulberry. Steyermark (1963) identified a single collection (Palmer 50832, from Lawrence County) as this form, but the specimen in Palmer’s herbarium at the University of Missouri, Columbia, has leaves less than 10 cm long. Uncommon plants with all of the leaves deeply divided into relatively slender, narrowly pointed lobes have been called f. skeletoniana (C.K. Schneid.) Rehder.