× Betula Sandbergii Britt. and its f. maxima Rosend. generally believed to be natural hybrids of B. papyrifera and B. pumila var. glandulifera Regl. occur in Tamarack swamps in Hennepin County, Minnesota.
Passing into the following varieties.
Betula papyrifera var. cordifolia Fern.
Leaves ovate, abruptly pointed and acuminate or acute at apex, cordate at base, coarsely doubly serrate, glabrous or pilose on the under side of the midrib and veins, often furnished below with axillary tufts of pale hairs, 1½′—3′ long, 1′—2½′ wide; petioles glabrous or rarely villose, ½′—¾′ in length. Fruit: strobiles ¾′—2′ long and ¼′—½′ thick, on villose peduncles up to ¾′ in length; scales glabrous or pubescent.
A tree rarely more than 30° tall, with slender glabrous or pubescent branchlets, and at high altitudes on the New England mountains reduced to a low shrub. Bark separating in thin layers, white or dark reddish brown.
Distribution. Labrador and Newfoundland to northern New England, and westward to the shores of Green Bay, Wisconsin, and those of Lake Superior, Minnesota (Grand Marais, Cook County); on Mt. Mitchell, North Carolina, at an altitude of 5550° (W. W. Ashe).
Betula papyrifera var. subcordata Sarg.
Betula subcordata Rydb.
