Sp. Pl.2: 986. 175
Gen. Pl. ed.5, 424. 1754
Widespread in temperate and tropical regions, North America, Europe, and Asia.
Species 10 (3 in the flora).
Morus nigra Linnaeus has been reported in floras by various authors (J. K. Small 1903, 1933; R. W. Long and O. Lakela 1971), apparently based on dark-fruited M. alba. It is native to Asia, commonly cultivated in Europe for its fruit, and locally naturalized in southern Europe. Occasionally cultivated in North America, it is not known to be naturalized. Because of the similarity to and confusion with M. alba, some American authors place it in synonymy with that species.
|1||Mature leaf blade less than 7 cm, abaxially harshly scabrous or pubescent, adaxially harshly scabrous; petiole to 1.5 cm.||Morus microphylla|
|1||Mature leaf blade usually more than 8 cm, adaxially slightly if at all scabrous; petiole 2 cm or more.||> 2|
|2||Leaf blade abaxially glabrous or with pubescence only along major veins or in tufts in axils of principal lateral veins and midribs, adaxially glabrous to sparsely pubescent.||Morus alba|
|2||Leaf blade abaxially pubescent or puberulent, adaxially with short, stiff, antrorsely appressed trichomes, usually scabrous.||Morus rubra|