Flora of North America species comparison

Betula pumila is sometimes treated (in part) as a variety of B. glandulosa Michaux, to which it is related at a subgeneric or sectional level. On the basis of morphology, however, it forms a cohesive and distinct entity (J. J. Furlow 1984). The two main varieties into which B. pumila is often divided (a more southern B. pumila var. pumila, with mostly pubescent, glandless leaves, and a more northern B. pumila var. glandulifera, with less pubescent, gland-bearing leaves) may represent geographic races; these are not well marked, however, and they do not hold up well when the complex is examined as a whole.

The Ojibwa used Betula pumila medicinally as a gynecological aid and as a respiratory aid (D. E. Moerman 1986).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Betula glandulosa is the characteristic dwarf birch of upland habitats throughout much of the mountainous west, occurring as well in dry open areas across the north. Where their ranges meet, B. glandulosa intergrades with both B. pumila Linnaeus and B. nana Linnaeus subsp. exilis (Sukaczev) Hultén, creating a confusing complex of intermediate forms. In the east, it reaches its southernmost limit on the subalpine slopes of high Adirondack peaks, including Mt. Washington, where it forms low sprawling thickets and scrubs.

Specimens of Betula glandulosa have been reported from the St. Lawrence Valley, but I have not seen them.

Wherever Betula glandulosa comes in contact with B. pumila, it forms a bewildering swarm of plants, known as B. ×sargentii Dugle, having intermediate states of most vegetative characters.

Plants intermediate between Betula glandulosa and B. nana subsp. exilis make up a continuum of forms linking the typical forms of Betula nana and B. glandulosa in parts of Alaska where the ranges of these species overlap. Wherever they occur in isolation, the species remain reasonably distinct and easy to identify. In southern Greenland, Betula glandulosa hybridizes with B. nana subsp. nana and with B. pubescens.

Betula ×eastwoodiae Sargent (= B. glandulosa × occidentalis) occurs in montane meadows and marshes in Alberta, British Columbia, Northwest Territories, Saskatchewan, Yukon, Alaska, Colorado, and Wyoming, where the range of the parents overlap.

Betula ×dugleana Lepage (= Betula glandulosa Michaux × B. neoalaskana Sargent) is common throughout Alaska and the Yukon, where the parent species frequently come into contact (E. Hultén 1941–1950, vol. 4; E. Lepage 1976).

Betula ×dutillyi Lepage [= Betula glandulosa Michaux × B. minor (Tuckerman) Fernald] is a putative hybrid that occupies the same general range as Betula minor. Like that species, however, it has not been studied experimentally. Careful examination of the entire complex to which this taxon belongs will be necessary before any of its parts can be truly understood. Betula ×dutillyi exhibits many of the same characteristics as B. minor, but it is slightly smaller in habit, and its leaves are smaller with somewhat blunter tips and more cuneate bases (E. Lepage 1976).

(Discussion copyrighted by Flora of North America; reprinted with permission.)