4. Betula uber (Ashe) Fernald, Rhodora. 47: 325. 1945.
Virginia roundleaf birch
Betula lenta Linnaeus var. uber Ashe, Rhodora 20: 64. 1918
Trees , slender, to 10 m. Bark dark brown, smooth, close. Twigs with taste and odor of wintergreen when crushed, glabrous, covered with small resinous glands. Leaf blade nearly orbiculate to broadly elliptic with 2--6 pairs of lateral veins, 2--5 × 2--4 cm, base rounded to cordate or truncate, margins irregularly serrate or dentate, apex broadly obtuse to rounded; surfaces abaxially glabrous to sparsely pubescent, especially along major veins and in vein axils, often with scattered resinous glands. Infructescences erect, ellipsoid-cylindric, 1--2 × 1--1.5 cm, shattering with fruits in fall; scales glabrous, lobes diverging distal to middle, central lobe ascending, shorter than lateral lobes. Samaras with wings narrower than to as wide as body, broadest near summit, extended beyond body apically.
Flowering late spring. Stream banks and adjacent flood plains in rich mesic forest; of conservation concern; 500 m; Va.
Betula uber , described in 1918, was not seen again until its widely celebrated rediscovery in 1974 (P. M. Mazzeo 1974; C. F. Reed 1975; D. W. Ogle and P. M. Mazzeo 1976; D. J. Preston 1976). It is apparently allied to B . lenta (W. J. Hayden and S. M. Hayden 1984; T. L. Sharik and R. H. Ford 1984); whether it constitutes a separate species or simply mutant individuals of B . lenta is a matter of controversy. Seeds obtained from the original single extant population of 17 trees and grown at the U.S. National Arboretum have produced an apparent hybrid swarm of offspring varying in leaf characteristics from those of B . uber to those of B . lenta (with which it occurs).