Description from Flora of China
Morus alba Linnaeus var. mongolica Bureau in Candolle, Prodr. 17: 241. 1873; M. barkamensis S. S. Chang; M. deqinensis S. S. Chang; M. mongolica var. barkamensis (S. S. Chang) C. Y. Wu & Z. Y. Cao; M. mongolica var. diabolica Koidzumi; M. mongolica var. hopeiensis S. S. Chang & Y. P. Wu; M. mongolica var. longicaudata Z. Y. Cao; M. mongolica var. rotundifolia Y. B. Wu; M. mongolica var. vestita Rehder; M. mongolica var. yunnanensis (Koidzumi) C. Y. Wu & Z. Y. Cao; M. yunnanensis Koidzumi.
Small trees or shrubs; dioecious. Bark grayish brown, furrowed. Old branches grayish black; branchlets dark red. Winter buds grayish brown, ovoid. Stipules 2.5-3.5 cm. Leaf blade elliptic-ovate, 8-15 × 5-8 cm, papery, glabrous, base cordate, margin triangular serrate with a few teeth double serrate, each tooth with subulate apiculum or seta, and apical serrations with long spines, apex shortly acuminate. Male catkins ca. 3 cm. Female inflorescences shortly cylindric, 1-1.5 cm; peduncle 1-1.5 cm. Male flowers: calyx lobes dark yellow, margin adaxially hairy; anthers 2-loculed, longitudinally dehiscent. Female flowers: calyx lobes glabrous or adaxially sparsely pubescent; style long; stigma with a nipple-like protuberance, 2-branched, abaxially densely papillate. Syncarp red to purple when mature, ca. 1.5 cm. Fl. Mar-Apr, fr. Apr-May.
The very distinctive leaf margin makes this species easy to recognize, in contrast to the varieties that have been proposed within it. Formal recognition of these varieties does not seem justified because they are based on features of indumentum and leaf shape, which vary more or less continuously.
Mountain slopes, high mountains, forests; 500-3500 m. N Anhui, NE Guangxi, Guizhou, Hebei, Heilongjiang, Henan, Hubei, NW Hunan, Jiangsu, Jilin, Liaoning, Nei Mongol, Shaanxi, Shandong, Shanxi, Sichuan, SE Xizang, Yunnan [Japan, Korea, Mongolia]..