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To this group of hybrids between M. baccata and M. prunifolia belong many of the plants that have been grown in gardens as Siberian crab or as Malus or Pyrus baccata. These hybrids differ from M. baccata in their larger fruits, which usually, though not invariably, bear persistent calyx-teeth at the top. Those which resemble M. baccata in having the fruits without calyx teeth can still be distinguished from that species by the larger size of the fruits and often by the greater downiness of the undersurface of the leaves, leaf-stalk, and calyx-tube.
When the hybrid Siberian crab first came into cultivation in this country is not known, but Bigg’s Everlasting crab (also known as the winter crab or Pyrus borealis) was, according to Loudon, raised in the Cambridge Botanic Garden from seeds received from Siberia in 1814, and this certainly belongs to M. × robusta. Other forms of this hybrid are known as the Cherry crab, the Red Siberian, and the Yellow Siberian, all of which were in cultivation soon after the middle of the last century. All have showy fruits which persist long on the branches.